All Square One’s electronics were mounted
on a piece of thick cardboard. It was definitely time for an upgrade.
Cardboard is pretty handy for prototyping robots. You can draw on it and
cut it to shape with scissors. It’s dead easy to make holes in it too.
Even better, it’s just strong enough to hold small bolts and screws.
I prototyped the chassis in cardboard. It
wasn’t strong enough to actually drive it around like that, so I swapped
to plywood before going any further.
The motherboard for the electronics was a different matter. It didn’t
need to be very strong because the chassis took all the stress. I
knew I’d end up rearranging the electronics a couple of times, so I
stuck with cardboard for as long as possible.
Time for a Change
It was definitely time for a new motherboard. I’d already rearranged
the electronics once to make more space but now I needed to add an IMU
and there was nowhere to put it. The cardboard had also got very
tired. It doesn’t look too bad in the photo, but it was definitely
past its best.
I’d decided that I was never going to run Square One with skinny wheels
so could afford to make the new board a bit wider.
There were several other changes I wanted to make as well:
- put the lasers on the centre line
- rotate the Pi so I can get the SD card out
- squeeze everything together a bit more to leave more free space
- leave space for time of flight sensors
- add an IMU
- leave space for the future
I made the new board out of 4mm MDF. It was thick enough for the bolts
and screws I wanted to use without being too heavy. The only downside
is that it doesn’t hold small screws very well. Plywood would probably
have been better.
Here’s what it looked like when I’d mounted all the electronics.
Comparing it to the cardboard version:
- it looks like there are fewer wires even though there are more
- there’s lots of space on the right even though I’ve added the blue
Here’s what all the bits are:
- Teensy 4.0 Microcontroller - Top Left - Light Green Box
- 4 DRV8871 Motor Controllers - Top Left - White Box
- Raspberry Pi 3 A+ - Top Centre - Pink Box
- LEDs and Button Switch - Top Right - Yellow Box
- Laser Pointers - Centre Left and Centre Right - Red Box
- ULN2803A Relay - Centre - Dark Green Box
- 5V Distribution Board - Centre - Orange Box
- LSM9DS1 IMU - Centre Right - Dark Blue Box
- 12V and 5V Voltage Regulators - Centre Bottom - Light Blue Boxes
- Power switch, fuse and battery connector - Bottom Left - Purple Boxes