You are exactly right – weight was the main issue. I am using a pair of slim USB battery banks. They are each the length of two D cells, however about half the thickness of a D cell. I’ve therefore added two short lengths of thin pipe full of ball-bearings and covered in tape, that sit on top of one of the USB battery banks above the motor bogie. There’s still just enough space to get the roof on. I have also glued the driving axel, so that now both wheels are driven rather than just the one. Previously the axel would spin along with only one of the wheels.
Those traction wheels look good. They might have to be the next upgrade.
This weekend I did a full strip down of the motor too, which now runs much smoother. So the Hymek is now performing very well!
This is the hardware configuration I am using…
It is a very neat modification, and you can get really responsive fine control from the web-server.
The only issue I am now having, is that at prolonged high power, the ESP32 will power cycle itself. I currently have no idea why – for some reason when the motor is driven at speed for a long time the motor driver is making the ESP32 unhappy. The simplest short term solution is to not run it near full power for a long time! To be honest this isn’t an issue – that speed is far too fast to be realistic for the radius of the curves anyway.
Thanks very much for your time.