My black motorized bobbycar chassis broke completely apart in Augarten (Graz) right before we wanted to head off to the hungarian hacker camp Camp++. I already had a red bobbyquad chassis laying around and most of the parts could easily be transplated. Also the colorful bobbyquad chassis were not produced for a long time already and back then they were made with a much thicker plastic than the black ones nowadays. I feel like the very old chassis will survive much longer.

First of all we have to butcher the old broken bobbycar. This is what was left from it:

The steering wheel will be completely redone with red 3d print parts to match the new chassis, also lots of new buttons will be added.

Lots of new buttons

How can you add so many new buttons when the number of GPIOs on the ESP32 is limited you may ask? The answer is on the left picture: the diods play an important role in that task!

The idea is that we use a GPIO as input but with alternating pull UP or pull DOWN configuration. The other side of the diode will be an output that will always be the opposite of the input pin. When the switch closes the input pull up pin will be pulled down through the diode. This mechanism allows us to detect any combination of button presses, but it makes reacting on buttons by interrupt hard / impossible. See the following wiring scheme as comparison:

This can further be extended to allow any number of buttons, my boarcomputer only comes with 8 buttons at this time but this might be further extended in the future.

New PCB for boardcomputers

Finally some other members of the bobbycar gang took their time and designed a pretty little PCB for the boardcomputer that has the display connector already prepared. Also it included better power rails to distribute the required voltages to different parts of the steering wheel like potentiometers, sensors and so on. It also featured some general purpose MOSFETs ready to be triggered by the ESP32 to turn on lights or HVAC climate machines on the bobbycar.

New battery pack

The old battery pack was just not compatible with the smaller holes in the red bobbyquad chassis. I have already had lots of 18615 battery cells from LIITOKALA laying around and after measuring the voltages of each cell I started forming 3 little battery packs that will all be connected in series afterwards with some XT60 connectors in paralell. The individual battery cells were connected with nickel strips. The spot welding machine was borrowed from the hackerspace.

Fun time while measuring all the voltages to make sure there won’t be any cross currents in the paralell connections of the battery pack. Also if any battery cell completely differs to the others it might be damaged and having different quality and capacity cells in series will make the whole battery pack unusable. The BMS would have to balance all day and waste energy.

Finished results

The new bobbycar really looks quite different from the old black one.

First accident in hungary

One of the motors might have had some screws loose and the magents inside the motor started scratching on the spools. The whole motor complteley overheated and the hall sensors all melted away, and after opening up the motor for inspection I was hit with this nice picture (It smelled awful!):

This required the whole motor to be replaced and the rest of the camp was fine.