So I'm a high school student doing some competition (a wallet-sized one, unfortunately) and I'm supposed to make an electric car. Think an RC-car, (about that size) without the remote control. I want to make one from scratch, so I decided on using an arduino for a micro controller. Unfortunately, I don't really have an adviser that's particularly knowledgeable about this stuff, so I decided to ask here. (brace yourself for quite a few possibly dumb and vague questions. I do understand this question will likely be edited/closed for being too vague, but if, by any chance, someone has answers, I'd also like explanations -- mostly because I want to learn something.)
I've decided on using an aluminum chassis and soft wheels, since the competition wants a car that can go as fast as possible. I've chosen soft wheels because that should give me higher friction, and an aluminum chassis because I want to reduce weight. Now, here comes the first problem. The competition specifies a maximum of a 9v battery to power everything, including the arduino and the motors. Now, of course, we only need to go about 10 meters (I just want sub 3s times). My original design involved having 4 separate dc brushed/brushless motors, and then connecting each dc motor directly to the wheel. The dc motors could be held on with brackets, and then connected to an Arduino connected to a MOSFET, at which point I could then use a motor encoder to see how far to go.
I now have a couple of questions:
- Should I try having a 9v to 12v converter? or a 9v to 24v converter? That might cut the current significantly, but I'd also be able to use a much more powerful motor. The problem I have with this is that it might be adding a lot of potential weight -- as I understand it, I can't convert directly from DC 9v to something else.
- I've decided on having a rear wheel drive rather than a 4wd -- but is it worth getting a gearbox and an axle and just having one motor?
- Should I use a gearbox at all? Or should I try to change the speed based on the size of the wheel I use?
- Would I try to maximize RPM or torque by getting a geared-down brushless?
- If I have a 9v battery, can I have 2 9v motors in parallel? Or is that unsafe because 9v is only nominal?
If anyone has tips on how to improve the question, I'd be glad to incorporate them into my edits.
some info, by the way:
- looking for sub3 second times
- using banebots 2-7/8 inch diameter wheels
- hard floor
- will need to back up after 9m
- only going straight, doesn't need to be able to turn
- thinking of a PID loop with a physical rotary quadrature encoder if one axle. thoughts?
- the car will be ~1kg and I won't be carrying anything else.