Latest video above made in April 2018. Fully working, fully controllable, machine is working really well now. Slightly click-bait front image for general YouTube consumption, sorry about that. The follow up video shows us going much faster a couple of days later and also how to bail out gracefully.
This is the wheel I ordered from China. It will run on 48 to 72 Volts. For now I will run it at 48V using the Headway cell pack from my previous "Lunar Rover" machine.
Cheap e-bike brushless motor controllers seem to be set up to go forwards only. I would like one that also will work in reverse and do the change from forward to reverse without any problems. I have found this Kelly controller model for electric boats. I do not know for sure if it will work so I have had to just go for it and experiment. It has a "joystick" mode which allows you to input a control voltage of 0 to 5V where 2.5V is all-stop, 2.7-5V is forwards and 2.4-0V is reverse. This therefore might just work. It can handle 200 Amps and this particular one will run at up to 60V (actually slightly more). The wisest first step seemed to be some bench testing in a test rig before I build anything unicycle shaped. In the videos above this is seen in video 1.
Next problem is how to convert the pulse width modulated pulses (PWM) from my Arduino (the brain of this machine), i.e. spikes of varying width at about 500Hz, to a smooth variable voltage to input as the control signal into the Kelly controller. I found on the DIY Drones forum a suggestion to use one of these. It takes the PWM and turns it into a smoothed voltage with no lag or delay. The simpler way to do this is to use a resistor and a capacitor to make an R/C filter. This will probably do the job but if you don't choose components carefully it can introduce a slight lag time, which I do not really want in a self-balancer. I did once make a self-balance skateboard that used an R/C filter in this way and it did balance. Anyway, for this project I chose to try using this DAC chip.
I made up the circuit diagram as above, exactly. Problem was, the chip is tiny although at least it does have some pins sticking out. I figured out a way to solder wires to these pins and make my own breakout board where the board was made of a square of card! I have tried to show how I managed this below. Also, you need some of those magnifying glasses you can get in electronics shops otherwise you cannot see what you are doing at all. Blu-tack is good for holding things, rest your wrists on the bench to steady your hands.
Above is the finished digital to (smooth) analog voltage converter. On the right is an Instructables article on setting up a resistor and capacitor R/C filter if you did want to try that instead. I did get the DAC to work in the end but it is pretty fiddly.
I started with a temporary upper frame but this is the version 2 taking shape. 20 Cell Headway LiFePO4 pack made cylindrical
and whole pack slides in from the front. Jet intake thing from an old aircraft forms the nose.
Steering assembly removes completely to allow the battery to slide in
Battery pack being inserted from the front end.
Battery pack in all its glory. Follow my video series for more on how this was constructed.
Here it is during March 25th 2018 early testing. Fuselage has now been changed to an aluminium tube. All balancing electronics are now in the 50's Ural motorcycle headlamp pod (see videos above) complete with 80's style retro talking alarms instead of a normal display.
Alarms are created verbally using something called Arduino "Talkie". This is software that creates 80's retro computer speech using a pulse width modulation output pin of a standard Arduino. Really cheap to do as you don't need a commercial speech synthesis board and retro-cool as well.
27/6/18: My previous front safety wheel did not look good and did not work either, you would have been over the handlebars before it hit the ground. I searched all the sci-fi vehicles and concepts on the web for cool ways to potentially disguise the front safety wheel and found the idea on the left. I mocked it up as in the centre photo and then built something similar for real as shown on the right. It works well too.