Design, Layout and Construction Tips
EE192

1.  Mount all of your circuit boards so that they are easy to access.   This makes life a lot easier when probing signals with a scope, replacing chips, or upgrading your circuitry.

2.  Design your circuits in a modular fashion.  Have well defined functional blocks with clear inputs and outputs.  Implement each system on a separate circuit board.  This will make it easy for multiple people to work on the car simultaneously in a productive fashion, as well as making it much easier to swap out a circuit for an improved version later on.

3. Prototype circuits on breadboards and thoroughly debug them before soldering together a finished version.  Don't just probe the inputs and outputs - check all the intermediate signals in the circuit to make sure that they are doing what you think they are doing (they rarely are on the first attempt).  Once debugged, solder together the circuit on a fiberglass & epoxy board (the ones with pre-fab copper traces are quite nice).  This will ensure that components don't wiggle loose & fall out when your car races around the track at mach 1.

4.  Wire wrap is great for interconnecting digital circuitry that is all on the same board.  Do not use it for inter-board connections.  The solid core wire will eventually break and cause you unnecessary head scratching.  I would not recommend it for sensitive analog circuitry (use soldered connections instead) - I've heard it is more susceptible to noise, although I don't have any practical experience with this.

5.  Use stranded wire for connecting various systems of the vehicle together.   Solid wire will eventually break if it sees any repetitive stress cycling from connecting two parts of the car that are vibrating in different ways.

6.  Size your wires appropriately (calculate voltage drops and power loss using chart) for the current they are carrying.  A good place to start is 14-18 Ga. on motor and batteries and 20-28 Ga. for everything else.  Don't use wire so small that it breaks when accidentally tugged on or caught on something.

7.  Use lots of different colors of wire, and pick a standard as to what each color means.  When running lots of wires, use ribbon cable or multi-conductor wire to minimize the ratnest effect.

8.  Use connectors to interface different circuit boards.  Again, a little time early on will save lots of time later as circuits are removed, tested, replaced, etc.   Molex makes a nice selection of connectors. 

9.  Think about the major noise sources in laying out circuits and wires on your vehicle.  The motor and associated drive circuitry is a BIG noise source.  The wires going to the servo will also be carrying significant (1A) spikes of current.   The DC-DC converters are also switching significant currents at very high frequencies.   Shielding and/or spatial separation of sensitive circuitry from these noise sources is something to consider.

10.  Mount circuits and especially sensors in a sturdy fashion.  You'll have plenty to keep you busy when tuning control systems - you don't want to have to deal with mechanical oscillations as well.

11.  Don't forget a power switch - check the rules.

12.  Make sure the differential is not too tight.  It should be easy to spin one wheel when the car is off the ground (and the other wheel will spin backwards).   It should also not be too loose (If you fix one wheel and spin the other, it should be able to drive the motor gear with quite a bit of torque before slipping).  If it is too tight, it will impair the ability of the vehicle to turn quickly.

13.  Either use nylon locknuts or lockwashers on the things that you mount (especially if the fastener is highly stressed).   Components routinely fell off of our vehicle from the vibrations until eventually everything was fixed with a locknut or lockwasher (at which point we had no further problems).