As the weather is still terrible around here, I spent the weekend working on my home automation. A load of general maintenance such as replacing batteries and fixing broken things like the integration with the burglar alarm.

I also added a few new integrations:

• DVLA Link – This lets me query details about our cars, and more specifically the due dates for MOT and insurance.
• Waste Management – Link into the local government to know when and what type of refuse collection is coming up.

But, the most fun one was finally getting the 10 inch display and Raspberry Pi mounted on the wall as a custom control panel!

I’ve had it sat on my desk for about six months and decided it was actually time to get it done. I had to CAD up a box for wall mounting and hiding the electronics. Not the best design, and lots of things to improve, but its functional.

A quick couple of holes in the wall, and it was mounted.

Once I have the local voice assistant details finished, this will get that installed too. That will need a redesign of the case to support some speakers and volume controls. The actual dashboard needs a bit more work, and possibly an LCARS theme as an option.

But at least its off my desk and working now. Very handy for a quick glance at the calendar, weather, alarm status, and also to view the front door camera.

Over the years I’ve messed with various home automation systems. From X10 in the early 2000’s, through Mi Casa Verde and z-wave going into the 2010’s, a few years using OpenHAB, up to the current day where I’m using Home Assistant.

Home Assistant has been around for a while, but I was loathe to move from OpenHAB as I already had a lot set up. However, as OpenHAB fell behind I finally bit the bullet and installed HAOS on a spare Raspberry Pi. This turned out to be a good thing.

I’ve been using it now for a couple of years, and it works really well as a central hub for all the different technologies in the house. This post is a quick overview of what I have set up.

Technologies

The beauty of Home Assistant is that it acts as a hub for many different home automation protocols, devices, and other information. A quick list of technologies I have integrated:

• Zigbee
• Z-wave
• ESPHome
• Matter
• Thread
• MQTT
• WLED

But not only does it talk to these home automation systems, it can also tie into other things such as:

• 3d Printers (Octoprint, Klipper, Bambu Labs)
• Google Assistant (Ties your home automation into google voice commands)
• Jellyfin/Plex
• Fitbit
• Raspberry Pi
• Roomba
• Smart Meters
• Printers (you know, the none 3d kind)
• Frigate (CCTV)
• Solar Production

And lastly, you can pull in information from web APIs to help with automations:

• Weather
• Sunrise/Sunset
• Moon phases
• Astronomy Weather (More detailed weather more geared to astronomers)
• Github (Monitor commits, issues, etc.)
• Whois (Keep an eye on domains expiring)
• DVLA (MOT and insurance due dates)
• Waste Management (get dates and types of refuse collection)

This is a lot of tech, and this isn’t a complete list of everything I have tied in, just the majority.

My Setup

So, enough of what it can talk to. How is my house set up?

Core

The main core of the system is a Raspberry Pi 4 running Home Assistant OS. This is a simple install onto a Pi and is fully managed by Home Assistant. Everything runs in containers and gives you everything you need to get started.

The Pi is run from PoE in a rack, to keep things simple, and also has everything installed onto an SSD drive as it is a lot more reliable that using an SD Card (My old OpenHAB system was on SD Card and I had to rebuild it every now and again as the SD card wore out). Plugged into the Pi are two USB dongles, one for z-wave and one for Zigbee/Matter. This direct connection lets me control the majority of the devices I have.

Also, installed as part of HA OS I have a few other addons. These are:

• InfluxDB – This keeps a historical record of all the stats in the house, which can then be pulled out into a Grafana Dashboard
• Mosquitto MQTT Broker – Some devices talk directly to an MQTT server, so this is running to fill that role
• ESPHome – A system designed to convert simple ESP32 or ESP8266 boards into home automation devices using a simple yaml language. Some commercial devices can also be flashed with ESPHome for extra functionality.
• HA Google Backup – Backups!!
• Lets Encrypt – Automatically renews my SSL cert
• VaultWarden – A locally run version of Bitwarden password manager.

These are all running on the same Pi quite happily.

CCTV (Frigate)

I have a second Pi 4 running a system called Frigate. This is an open source CCTV system that integrates really nicely with Home Assistant. It also has functionality for not only motion detection but facial detection too so that it will only trigger if it detects a human (not a cat or squirrel) which definitely helps cut down on false positives. I have had to block out certain areas for detection tho, as in high winds it sometimes thought some of Joy’s flowers were a human!

I’m hoping to upgrade this to a Pi 5 when the PoE hat comes out, as I currently have 4 cameras going into it and it does struggle a bit. I do have a USB Coral AI stick from Google that I can offload some of the more AI related tasks too.

NAS (TrueNAS Scale)

I do have a NAS box set up that has a simplified Kubernetes system installed. On this I run a few other services, including Grafana for viewing stats of my home, Spoolman which keeps track of my 3d printer filament usage, and Trilium Notes for keeping track of the random things in my brain.

Other Hardware

So what have I actually got set up?

Most of the main lighting in the house are Phillips Hue lights, with their dimmer controllers. However, since realising just how much data the Hue hub was sending back, I removed that and now everything is directly controller via Zigbee. The only main exception to this is the garage which initially had fluorescent tubes and I use a z-wave in wall module to control that.

I’ve a lot of smart sockets around the house too, from plugin units to actual in wall faceplates. The vast majority of these allow for energy usage collection too so I can not only turn things on and off remotely, but I can also monitor the energy usage of various items such as 3d printers, server cabinets, desktops, TVs, etc.

The burglar alarm is also connected in, which turns all the various door and motion sensors into sensors that Home Assistant can use for automations.

WLED is a system to install onto an ESP8266 or ESP32 to control a string of RGB LEDs. I’m starting to incorporate more of these into the setup and they tie very nicely into Home Assistant

Control

What does all this gain me? The main benefit is a single app on my phone to control everything. I don’t need a Hue app, a Roomba app, to access a webpage to control my WLED lights, etc. I can create a dashboard on Home Assistant to give me a nice overview of the controls in the house. For instance, my setup main dashboard consists of an overview page (simple controls such as lights, along with main thermostat control and some other status) with the ability to click a room and get more detailed controls and information. That covers about 90% of everything.

Along with this, as I have Google Assistant integrated, I can also just ask google to turn lights on, set the thermostat, etc.

Automations

So far, most of the stuff is just allowing for remote control, but the real beauty is making things automatic. I’ve only really got some basic automations done at the moment and want to expand on this in the future.

• Automatic outside lights. I have the lights set to come on at sunset, and turn off at midnight. They’ll also come on in the morning if Joy is going to work and its still dark out.
• Turn the thermostat down at night. The thermostat will drop a couple of degrees at midnight whilst we’re asleep to save some energy. I have got the alternative set to turn it back up in the morning, but thats disabled for now as its just as easy to turn it up manually depending on what time we get up.
• Send an alert if someone comes to the front door, and turn the light on. This is one of the reasons I want to upgrade the Frigate Pi. The Pi 4 is just a little slow on this, and hoping the extra processing power will speed things up.
• Show video feed on my google home displays when someone is detected on the front door camera.
• Automatic office lights. I’m terrible at remembering to turn my light off in the office, so I have a simple motion detector to automatically turn the lights on and off. They do turn off occasionally if I’m in the office concentrating on something and not moving much (such as writing a blog post about my home automation system) so I’ve just ordered some mm wave detectors to try which should be more sensitive.
• Notifications when prints have finished or theres an issue.
• Daily notification if a battery is low in a device. All my Phillips Hue Dimmers were bought at the same time, and I’ve just had to replace all the batteries at once!

Theres room to do a lot more of course, but these will do for now.

Monitoring

So, I’m a nerd and I like stats. One of my favourite things that Home Assistant does is store historical data so that I can pull information out and graph it in Grafana. I’ve no idea if this will have future uses, but it does produce some pretty pictures such as the one on the left that shows temperature and humidity over time.

Also, Home Assistant has an inbuilt energy dashboard. You can select the various entities you monitor for energy usage from smart meters or solar panels, and it will generate a nice dashboard to show your energy usage.

Water consumption is on there because it seems UK water meters broadcast their readings unencrypted on a band that can be read with a cheap USB dongle. I wrote some python to read the meter and push the stats into Home Assistant. I also wrote some software to run on a Pi connected to my two solar systems to read the meter information there and push it into Home Assistant.

I’m hoping once I’ve collected data for a full year, I can work out if I can get a decent ROI on a house battery.

Future Plans

One of the big things at the moment is LLMs (I won’t call them AI!) and Home Assistant can actually make use of them right now. This means I can replace all my spyware Google Homes with a fully local solution running on some low powered Raspberry Pi zeros, using a local LLM for more natural language communication. Plus you get the ability to add custom wake words, which will be fun.

I’ve also got a Pi with a 10 inch display on my desk that I want to turn into a control panel to put somewhere in the house, possibly in the entrance way.

Wow, its been so long since I’ve done a post on this blog! So, here is a list of projects I am currently using a Raspberry Pi for. Occasionally this comes up in conversation, so I thought I’d compile the list here.

• Octopi
• Klipper
• PiHole
• Home Assistant
• Frigate (CCTV)
• FlightRadar24 Plane Tracking
• 2 x Astromechs
• EmonPi Hub
• Telescope Control
• CNC control
• RetroPi
• Astropixels Demo control
• Reflow oven (wIp)
• LoRaWAN gateway
• ROS robot
• Allsky camera (wip)
• K8s cluster (4 Raspberry Pi)
• 2 x Solar PV Monitors

Then I also use one for the Droid Driving Course, with a couple of Pi Zero for monitors to display results.

The list is ever changing. I would love to run a K8s cluster at some point, but it looks like the shortage of RPi isn’t going to let up any time soon.

SDR Radios

One of the things I’ve been getting into recently is using Software Defined Radios (SDR) with cheap USB digital TV tuners that are available all over ebay, etc. These have been taking the radio community by storm as the chipset in them from RealTek can tune into a really wide band of frequencies. Usually from down around 20MHz, all the way up to nearly 2GHz.

Tracking the skies

One of the fun and cheap projects you can do is track all the aircraft that are flying around you. All commercial and some light aircraft are required to have an ADS-B transponder that sends out a radio signal on 1090MHz that contains their location, speed, etc. These signals can be received with one of these SDR dongles and decoded to display this information on your computer.

There is even a ready made piece of software called dump1090 (and many, many forks of it) that will also display this information on top of a google map.

Antenna

The first thing you will need is a decent antenna for receiving these signals. The easiest to make is a quarter wave ground plane. In the simplest terms, this means that the main part of the antenna is a quarter of the wave length of the signal. The equation for this is:

f = c / λ

where f is the frequency, c is the speed of light in m/s, and λ is the wavelength. So to get the wavelength of 1090MHz, you rearrange the equation to:

λ = c / f

Putting the correct numbers into this means that a quarter of a wavelength is just 68.8mm. This makes for a pretty small antenna.

The ground plane is just four more wires at 90 degrees to each other, and bent down at a 45 degree angle.

All these wires are then soldered into a standard SO239 panel socket.

There are many sites that will give a much better walk through of how to make one and the details behind it.

Software

Next, we need to look at the software. At this stage, if all you want to do is have a quick look for some fun, all you need is the antenna, usb stick, and the dump1090 software from one of the many forks (If found the dump1090-mutability one to be best). Download or clone this repo, and follow the compile instructions to give it a try. You should then be able to view the results either on screen or via a web browser.

The other option if you are going to go for a more permanent solution is to maybe use the data to improve a commercial sight such as FlightRadar24. This is what I chose to do, so I signed up for an account with them and followed the instructions to build a dedicated Raspberry Pi receiver that will automatically upload any information I receive to their systems, hence improving their reliability. This also gets you a full business account on there worth $500/year!

Enclosure

Lastly, if you’re doing a permanent solution, you need somewhere to put it. To save space and cost, I just used a Raspberry Pi with an decent sealed enclosure box.

I used some epoxy to glue the antenna on the end of some 20mm conduit that I had, with the cable passing down through it. Then drilled two holes in the box. One that I put a rubber grommet in to pass the power feed through, and the other to put an external antenna connector through.

Lastly, I used epoxy again to fasten some 20mm brackets to the box lid for the antenna to attach to. This was better than screwing, as fewer holes for moisture/bugs to get in through. Then I just mounted the whole thing on the side of my garage and passed a cable for power to it.

Ideally it would be placed higher, or at least the antenna would be, but that started to make things complicated. As it is, I can still get signals from planes nearly 200 nautical miles away.

Summary

Now I can access the Pi whilst I’m on my network and view all the planes around me. I also have a full business level account with FlightRadar24. Is there much point? Nope, not really apart from helping crowd source data for a company. Why’d I do it? Because I can and its fun!

R2 is progressing nicely, solar stats are gathering, and I’m waiting for parts for my powerwall project. To add to the list of projects, and to learn techniques on the lathe and mini-mill, I’ve decided to build my own lightsaber.

If you want a lightsaber, there are plenty of options. Cheap ones, off the shelf decent ones, upgraded ones, custom ones, and even kits. As I want to learn machining skills I am going down the custom DIY route.

Saber Parts

A saber in its simplest for is:

Sound Board

This is a small board with an accelerometer, LED driver, speaker driver, and a couple of inputs for buttons, with a microcontroller to tie it all together. From research and conversations with my friend Neil (who has his own saber shop, London Sabers) I decided to go with a sound board from a company called Plecter Labs. This is a home run shop that produces a range of sound boards of differing complexity. The boards can be bought in the UK from JQSabers. That is also where I got a lot of the other parts that I needed.

LED

These days you have a choice between a single LED cluster in the hilt, or a string of LEDs that run up the inside of the blade. With a string of LEDs you can have a gradual light up of the blade that looks more like the film, but with a single LED cluster in the hilt it makes the blade a lot easier to remove. To keep things simple, my lightsaber will just have a single LED cluster in the hilt. I’ve gone with the Tri Cree XP-E2 which has two blue and one white LEDs on a small circuit board. The white LED allows for something called ‘Flash On Clash’ which, as  it sounds, means that when the sound board detects that you’ve hit something, the blade will pulse with an extra white light.

Hilt

This is the part that will be 100% custom for me. There are modular options available, or replica ones if you want something from the film. I’m doing a totally custom design and will all be machined by me on the lathe and mini-mill. It will be a fairly simple design (for this one at least) as my skills on the lathe are not exactly the best yet.

Blade

The blade is just a simple tube with reflective film on the inside to give a smooth lighting. As I want to be able to hit things with my lightsaber, I’ve gone for the thick walled dueling blade.

Progress

So far, I have made the emitter and main part of the hilt, along with doing a test wiring of all the electronics to go inside of it. Quite pleased with how the hilt is coming along, I just need to wait for my new mini-mill to turn up so that I can accurately drill some holes and create areas for the switch to sit. The pommel end of the hilt still needs to be designed, and will house the main speaker. Currently I’m working on some laser cut parts that will hold the internals in place, yet still be easily removed for servicing.

The next step in my solar power quest is to get a decent amount of storage. To that end, I’m attempting to make my own 18650 power wall using all the recycled cells I’ve been harvesting.

Power Wall Design

I’ve been watching a lot of DIY power wall projects, including HBPowerwall and Jehu Garcia. Unlike my batteries for R2 which will be charged and discharged with me present, a power wall needs to be left unattended for extended periods of time usually. Mine will be in the garage and I’ll only be physically present when working on projects in there. This means that I need to add some extra safety features into it such as fuses.

Fuses and holders

A lot of people have been soldering fuse wire directly to the 18650 cells, but this is something I want to avoid. Firstly, this runs the risk of ruining the cell. Secondly, I’d like to easily be able to swap out failed fuses and cells. One person I’ve been watching on YouTube is Adam Welch who had a nice idea on how to solve both these issues. I’m extending on his idea by using fuse holders and standard 5x20mm fuses. Along with this I will be using some standard PCB mount 4 x 18650 holders.

The holders will allow for quick swapping of any dead cells, not that I’m expecting that to happen too often but I am using recycled cells with unknown service life.

PCB Design

To make this a bit more professional I’ll tie all this together with some custom PCBs that I’m currently getting made. The PCBs will join two holder trays together and mount the fuses to them.

There will also be an edge connector designed into the PCB. The final idea will be for modular shelves that can be added into the main battery as I build them by making a backplane that they plug into. The backplane will have rows of sockets, and also house the BMS system that I want to add to further protect the battery and cells. It also gave me a chance to try out KiCAD rather than Eagle CAD that I had been using for projects up to this point.

Aims

Whilst this approach won’t be anywhere near as energy dense as something like the HBPowerwall project has accomplished, it should allow me to have a nice small scale, safe, installation.

No way I’ll ever do something like this tied to the grid, but it should be enough for lighting and charging my tool battery packs at least. With only 100W of solar panels at the moment, a single bank of cells will give me a little more energy storage than the two SLA ones. Adding a second will hopefully take this up to about 400Wh of storage. More than enough for my needs.

Still messing with the monitoring of the solar, seems to be working ok so far. However, there is currently no load on the charge controller which means it enters float charge and doesn’t show the actual amount of energy I could produce. I’m going to start wiring in a load of some form to get better stats.

 

 

I got a message a few weeks back to see if I was still looking for old laptop batteries for 18650 harvesting, and of course I said yes. The next day, I got one or two batteries dropped off at my house:

Wow. Its going to take some time to crack them all open, harvest the cells, and test them all properly. Of course, I’ve got two batteries for R2 now that seem to be in a good shape and last long enough for pretty much any event. So the question is, what do I do with all the cells I’m going to have once I’ve finally gone through all these crates.

I’ve a few projects in mind that will utilise a couple of cells each, including a standby battery for R2’s brain, but a rough calculation shows that once I’m through all these crates I’ll have approx 1200 cells of varying states. So far, I’m through about half a crate and the vast majority seem to be in a good condition and over 2000mAh capacity. That means I’ve got nearly 8kWh of energy storage! Even if I assume half the cells are dead (so far only about 2% seem dead), thats still 4kWh.

The first thing that jumps out for this amount of storage is a form of power wall. Now, I’m not going to do anything grid tied, that is just too much hassle, but doing something off grid for the garage is definitely doable. If I can perhaps do enough to run the computer and other electronics, plus indoor and outdoor lighting, then I will consider it a success.

To start the project, I got hold of a few small solar cells, one 25W, and a couple of 50W ones. The 25W one will be used for experimentation and testing theories out, and the two 50W panels will be mounted on the wall of the garage for a more permanent solution. I also purchased an EPSolar MPPT charge controller, to go with a couple of spare 12V SLA batteries I had spare from initial testing of R2. I went for this model as it has a serial out port on it that will allow me to tie it into my OpenHAB home automation system and graph things like battery charge, solar power production, and any load on the system.

Being able to graph those details will allow me to make an estimate of how much energy I can generate on a typical day, and from that calculate how much I can actually run off my system for a given amount of solar panels, and also work out just how many kWh of energy storage I need.

The charge controller however will only work with standard lead acid batteries, whilst I want to make use of the 18650 cells. To this end, I did a lot of reading and it seems that there are very few hobby level solar charge controllers that will work properly with lithium technologies. Some charge controllers can be made to work with them, but it is more of a bodge.

After much searching, I did find one chinese charge controller that said it worked with lithium batteries, and actually seemed to back that up in the details. One of the main things to look for is that it supports the typical CC/CV (constant current/constant voltage) charge methods that are required for all lithium cells. A few clicks, and it was on its way on a slow boat from china.

For now, I’ve got the EPSolar charge controller mounted on the wall of the garage, connected to the 100W of panels outside.

Next steps are to get some data logging from the serial port, probably using an ESP8266 based device, dumping the data into my MQTT server, which in turn will be monitored by OpenHAB to be dropped into an influxDB store for graphing with Grafana.

Along with this is the slow process of breaking open a lot of laptop batteries and harvesting the cells. Once I have enough for a decent sized test, I will be looking into various ways of mounting them and hopefully adding an individual fuse to each cell for safety. More research into BMS for making sure the battery is properly balanced is required too.

 

 

There are many options for a battery to power an astromech, from the tried and tested Sealed Lead-Acid, to the latest LiFePO4. This article will look at utilising the very common 18650 cells. These are used in power tools, laptops, even Tesla cars.

WARNING, this article will talk about opening old packs, harvesting their cells, soldering cells, spot welding cells, and lots of other things that could be quite dangerous.

Lithium cells of any type can heat up or burst into flames if mistreated. Only attempt the things in this article if you are entirely comfortable with any possible outcomes. Do other research, read other articles, the author accepts no responsibility for any injuries or death from the instructions given.

General theory

18650 refers to the size of the cells, 18mm x 65mm. They generally have a capacity between 1500 and 3500mAh. If you see anything saying 4000mAh or above, chances are its a scam. There are a lot of cells branded ultrafire that claim over 6000mAh capacity which is a total lie. Voltage ranges from 4.2v when full, to 3.2v when empty. These cells use Lithium-Ion technology, which is a lot safer than the Lithium Polymer that is used in many radio control devices. The drawbacks are that it has a much lower discharge rate. LiFePO4 are even safer, but are also more expensive. Li-Ion seems to be a middle ground, which is why it is used in so many places.

Generally, these cells are arranged in series/parallel to get the desired voltage and capacity. For example, a 24V battery is made of 6 cells in series. Extra capacity is added by putting more cells in parallel, so that if you use cells with 2500mAh capacity and want a 24V battery with 10Ah capacity, then you will use 4 rows of 6 cells, commonly written as 6s4p.

The current drain allowed on a battery is usually 1C, or 1*<capacity>, so in the same example 6s4p battery, you can have a maximum drain current of 10A. Doubling the battery up to be a 6s8p will give you 20Ah and a 20A potential drain. 1C is the safe limit using recycled cells. If you are using brand new cells then you may be able to get a higher current draw by checking the datasheet. For example a NCR18650B can draw 2C and a NCR18650PF can go up to 3C.

Sources

Cells

As mentioned above, 18650 cells are used in many places, and can generally be recycled. The best place I have found for second hand cells is from laptops or power tools. These battery packs can be cracked open and the cells removed. It is quite a labour intensive task, but saves a lot of money. You can pick up job lots of second hand cells from eBay, tho this is getting more expensive as more people are harvesting cells this way.

You have to force the two halves of the battery case apart, usually with a screwdriver or similar flat sharp object, and then separate the cells from the circuitry and cabling inside. Always wear heavy gloves, and take extra care when using a lot of force. Its easy to slip and damage yourself or the batteries. Also make sure to take care not to use the cells as a fulcrum as this will also damage the cell. Basically, be careful and take your time.

The drawback is that each cell is of unknown capacity and life, some cells may even be totally dead. They could already have been through a few thousand cycles. Each cell needs its capacity testing with a charger/tester such as the Opus BT-C3400. Of course, if you can ask friends and family for donations of old laptop batteries, you can save even more money. I managed to get a lot donated for free. Despite the drawbacks and amount of work required, you can end up with a battery for next to nothing that would cost a lot if you bought a ready made one. For example, I built a 24V 25Ah (approx) 6s11p for around £50 of cells, plus a few other bits.

The other option is to buy brand new cells in bulk. Either from Chinese sites such as aliexpress.com, or from other sites closer to home such as eu.nkon.nl. Chinese ones are generally a little cheaper, but you do have a long lead time and the risk they are counterfeit. A typical cell such as the NCR18650B (high capacity/average discharge rate) or NCR18650PF (medium capacity/high discharge rate) can be bought for approx £3 a cell.

Additional

As well as the actual cells, there are a couple of other essentials. These are cell spacers, which clip into various configurations to hold the cells in place, and allow air flow around them. You’ll also need nickel strip to connect all the cells together. Both of these items can be bought from aliexpress.com in bulk. If you are buying brand new batteries from NKON, they also sell nickel strips for a decent price when bought in batches of 10m.

Lastly, you’ll need battery connectors and a balance lead. The battery connector can be anything you wish, as long as it will take the current. The balance lead is a connector so you can make sure that all the series cells are at the same voltage. This is important so you don’t let one cell run down lower than the others, which will potentially damage the cell, and maybe the whole battery. You need one for the correct size of battery (eg, a 6s battery will need a 7 wire balance lead) which can be got again from aliexpress.com or ebay.

Constructing the battery

Once you have enough cells together, and all the other items, time for construction. The general process is:

1. Sort the batteries into parallel sets with the same total capacity. The idea is to have them well balanced before you even start. You can use a site such as repackr.com to help with that
2. Clip the cell spacers together in the required layout (eg 6×12 for a 6s12p), then lay the cells out. Each parallel set should be the same orientation (eg, negative to the top), but alternate them as you fill in the series set.
   

   The start of a 6s12p pack. Can see the parallel sets run down the picture, with the series sets alternating across

    

3. Once you have all the batteries in place, clip the top of the frame into place
   

   Here is a small 3s5p pack, ready for the nickel strips

    

4. Now its time to connect the parallel sets up. Using either a soldering iron, or a spot welder, connect strips along all the parallel sets. These are the ones that are all the same way up. What this does is create the capacity for battery pack. Be careful if soldering, don’t allow too much heat to build up on the cell, do it as quick as possible. You can get spot welders from aliexpress.com for around £200 that will do the job a lot better.

   You can also get a device that will give you a full readout, just from plugging the balance connector in. They are only a few pounds from places like ebay. They will let you view the total voltage, each parallel set voltage, and also the max/min/dif between the cells.

   

   For the initial charge you will need to use a decent balance charger, such as an imax B6. These are generally for lipo batteries, used in radio controlled quad copters or planes. The benefit of a charger like this is that it will balance the cells out and has lots of monitoring and protection built in. Follow the instructions in the charger manual closely.

   Testing

   Once charged, leave your pack for a while, even a month, testing the voltages periodically. If you have a dead cell, then it can manifest as one of the parallel sets slowly loosing charge. When this happens, you’ll have to dismantle the battery and retest all the cells.

   If you have the time, you can also do a full discharge test with the charger on the battery to get an accurate reading of its capacity. This will take a long time if you’ve made a big battery, depending on the charger you use. If you aren’t overly bothered about an accurate capacity test, just run the battery in the droid (or whatever other use) and monitor the voltage. Don’t let the voltage go down below 3*<number in series> (eg, a 6s should never be let to dip below 18v). To prolong the life of the battery, don’t even let it go that far. Full charge/discharge cycles are the worst case for wear on them, and will shorten the lifespan. I recommend discharging it to around 40-50%, at least on the first try.

   After the first discharge, check the balance of the cells again. Ideally there should be little difference between them in a fully functional battery pack. If there is significant difference (IMHO, 0.1v between the highest and lowest voltage) then you may have a bad cell somewhere. Do another balanced charge and discharge cycle and see if the same cell has troubles. If it does, rip it apart and try again.

   If the battery remains balanced, then you can actually use a none balance charger (cheaper, and usually higher current for rapid charging) for most charge cycles. Tho make sure it is balanced occasionally and no harm in doing a slow balanced charge once in a while.

   Conclusion/Notes

   Using 18650 cells gives you great flexibility in not only the size (voltage and Ah), but also the shape. This example has shown creating standard blocks, but with some creativity you can make a battery that follows a certain shape (ie, follows the outer curve of an R2 unit’s interior). If you want to make use of recycled cells, then this is a very cheap option to get some very high capacity batteries built. Even buying brand new cells will still save you a lot of money.

   For example, I’m currently building a 6s12p pack using NCR18650B cells. I’m getting these for approx £3 a cell. That makes the total cost of cells £216, which gets me a 24V/40Ah capacity battery in a fairly small form factor that can give out nearly 80A (my droid barely pulls 10A at full speed!). I doubt I could fit enough SLA batteries in my droid to get that, and a similar capacity of LiFePO4 would set me back about £800. Even taking into account the cost of a spot welder (which can be used many times of course) its double the price.

   Further research

   One thing I haven’t covered in this article is a BMS. This is a Battery Management System makes sure nothing is going wrong with it, and will cut off the output when the battery gets too low. I’m still researching these myself, and will possibly mess with them on my next pack. IMHO, if you are keeping an eye on the battery voltage during use and doing periodic balance tests and charges, then a BMS is not necessary.

   Also note that capacity of the cells will drop over time, depending on number of cycles, how deeply they were charged/discharged, and how rapidly they were discharged. Take care of the battery, and it will last longer, drain it constantly at high current and it will be dead within a few hundred cycles.

    

Hi, my name is Darren and I’m a serial hobbiest.

Well maybe not that bad, most of my hobbies are pretty much related (electronics, computers, science), and a lot are things I’ve been interested in since I was a kid. Most recently, I’ve invested in a fairly decent telescope and mount to do some visual astronomy, but more for astrophotography. I want to take pretty pictures of things very far away! So after a lot of reading of various blogs and websites (Star Gazers Lounge forum is fantastic), and watching numerous youtube videos, I got a tripod for my camera and a couple of cheap lenses off eBay. That is all that is needed and you can get some half decent shots.

My astrophotography album

But it wasn’t enough. So I dove back into the forums and did even more research, and learnt a few important things.

• Telescope – Numerous different types, mainly split into reflectors, refractors, and catadioptric. All have their benefits and downsides, but for doing astrophotography the telescope isn’t the most important item surprisingly.
• Mount – This, for astrophotography, is the most important thing to get right.You need to have a solid mount for doing anything more than a few seconds exposure, and one with tracking in Right Ascension at least, to track the stars. And it really needs to be an equatorial mount to avoid rotation of the starfield as it rotates.
• Eyepieces – You need eye pieces to view through a telescope, and the shorter the focal length, the greater the magnification. These are generally only used for visual astronomy, as cameras bypass the need.
• Camera – Most DSLR cameras block out a large part of the infra red by design, but you can get them modified to remove this filter and get much more vibrant images. Its not a necessity, but definitely a nice to have.

Whilst learning all this, I had a thought in my head about some form of computer control (Linux based, of course) and actually stumbled upon a few projects to help with this. The first was AstroEQ which was an opensource ‘Goto’ system (select a star, and the telescope will automatically move to center on it) designed around an arduino. That was a perfect start for me, and I was pretty sure I could get it working from Linux. Thats when I discovered indilib!

Indilib is an open source system for controlling all sorts of astronomical instrumentation, not just goto mounts, but also things like auto focusers, digital camera, filter wheels, and other custom devices you may want. Even better, all this can be run from a Raspberry Pi as the control server and a laptop using the actual astronomy software. This would mean I could set it all up, and retreat to somewhere a little warmer to actually do my observations and photography. I’m sure this is against the amateur astronomers code or something, but damn it gets cold out there.

Along with indilib, there is kstars. This is a planetarium program written for the K Desktop Environment, and with EKOS plugin can control any indilib hardware. Not only that, it can schedule work and sequences, and help you plan your observations.

I’m going to (try to) write more blog posts chronicling my progress on getting all this set up, and some HowTo posts on using indilib on a raspberry pi, with kstars, and any custom hardware I make.

Its been a long time since an update, but we moved house at the start of the year and things have been hectic. At least, thats my excuse and I’m sticking to it! I have been making progress with R2 in the last couple of months, doing a lot of work on his brain for starters, and painting various parts.

Code wise, there has been a couple of fairly drastic rewrites since my last update. The interface is a REST API, which sends commands to various modules as before. I’ve added a scripting module now, so that scripts or loops can be initiated such as random sounds, or a dance routine. The servo module had to have a major rewrite too as I discovered that I could only control one servo at once and had to wait for that to finish before another command could be sent. That wasn’t much good! I’ve also written the first of the actual controller interfaces (not counting a simple web one for testing), R2 can now be controlled from a PS3 controller. Button combos are read in from a csv file to trigger certain effects or scripts. Lastly, R2 now has a voice, and can play any mp3 stored in a directory, including selecting random ones from a list of types. Next step is to get either the Pi or the A la mode Arduino to control the speed controllers. I don’t want to run them off the Adafruit i2c servo controller for safety, I’d rather drive them directly and have some form of watchdog to make sure R2 doesn’t go on a rampage. All the code is still available on GitHub under my user, dpoulson

The PDU also needed a rethink, not least of all because of the amount of current it needed. The setup now has feeds directly to the speed controllers, with relays on the output from them to the motors so I can break the circuit if needs be. These relays will automatically turn off if the battery is disconnected so that any pushing of R2 will not feedback into the speed controllers and fry them. The relays will also be controlled from GPIO pins on the Raspberry Pi so I can disconnect them via an API call. I’ll also have an input for a kill switch that will have to be permanently on if any of the motors are to be powered, possibly using a transmitter in a replica droid caller or hilt of a light saber. I’ve a base idea for the new relay controls:

 The relays I’ve found are Omron G4A-1EA, which have the benefit of the switched load being on spade connectors on the top, rather than through PCB traces, which when I did the calculations would need to be massive to support the potential current running through them. This allows me to make a simple PCB with the controller circuit, and hook the 24V battery up to it to power the coils. If the battery is removed, the coils turn off and the circuits are broken. No fried speed controllers.

The 24V connection will probably go through the fuse box I’ve installed, with a hefty fuse. The makers of the speed controllers don’t actually recommend a fuse but I’ve seen a few comments saying a 60+A fuse can’t be a bad idea, just in case!

The battery will connect directly to the center contacts of a DPDT switch, with the fuse box on one side, and the charger connection on the other. This will allow charging the batteries without taking them out of the droid. Not sure if this is best practice or not, needs more research. Currently they are just a pair of 12V SLA batteries that I had, connected in series to give the full 24V.

I’m hoping to get some time either this weekend or next, to hook up the motors, speed controllers, and battery, to test them out and get an idea of potential current draw. They’ll be controlled with a standard RC transmitter/receiver for now. If I can get the legs onto R2 he may even be drivable by xmas.

Fingers crossed!