Hey Roger! I don't think it would be very difficult at all. Just find some descent higher voltage mosfets and diodes. You might be able to just use a single mosfet/diode pair, and maybe 2 or 4 400v filter capacitors. It's not that hard to get the code to ramp up the throttle slowly if you want it to come on pretty gradually.
It would be much easier to do this than regular code. It would take like an hour of messing with the program. You may not need hardware current limiting in this context. It could be a much simpler control board. Maybe still a thermistor?? I don't know. 14 amps is pretty puny compared to 500. I doubt heating would be an issue, either.
I would love to get the control board made! They are all "through hole" components. I'm not sure how optimal the layout I used is. What I did before was just superglue 2 prototype PCBs from radio shack together, and solder everything with wires, trying to give some thought to layout (like where the digital grounds connect to analog grounds). It was exceedingly tedious.
To have a board, where all you do is push the components through the holes, and then solder away! Man, that would be so dang awesome, I can hardly stand it. I just want to make sure that the layout is done in a pretty good way, and I am NO expert on board layout. What I did works. In fact, my car drives very very smoothly now.
It's true that perfect is the enemy of good, so I don't know! What to just choose a layout that is similar to what I did, and call it good? It would be much easier this way than the radio shack way.
Getting a PCB made would still allow for different values of resistors and capacitors later. You would just plug in whatever you wanted into the holes! So that still would offer some flexibility.
A friend of mine recommended
Futurlec - PCB Manufacturing Service and PCB Production
He said it's the cheapest place he has seen for the hobbyist.
I have ExpressPCB software, which allows you to do the pcb layout and submit it to futurlec.com, but I've never used it before. I only used ExpressSCH, the schematic part of the software. I could try to figure it out. The whole controller would be DRAMATICALLY simplified once the control board becomes just a plug and solder thing! I wonder if they allow labeling on the pcb, so anyone would know where to plug in the components? If not, a master picture could be printed on the computer.
Pricing Example:
for (10) double-sided 4" x 3" PCB's it would be $7.74 per board with $25
setup. That's $10.24 per board.
If you add soldermask, the cost per board would then be $12.64 per board.
(Note: That's the example that my friend gave me. I would probably want to do single sided pcb, because they are through-hole components)