Let's Make Robots!

Three-wheeled electric mountainboard *in progress*

If you're not careful it tries to kill you...

My electrical engineer neighbor gave me six 12v led acid batteris- YAY!   These will most likely end up in a sumo robot for next years National Robotics Challenge, but I was hasty to find something to do with these using the materials I have now.  I had scavenged a broken electric dirtbike months before, and decided to build an electic mountainboard using that rear drive wheel and the six batteries.  I made a front truck using a block of aluminum, steel rod, and wood.  The rest is extremely simple, my curent control mechanism is simply a button you push to go- its either off or full speed.  This makes getting started difficult without being thrown to the concrete.  

Anyway- soon I will put a video, a better explination, and some pictures up.  In the meantime, how could I make a control mechanism that allowed for variable speed? any ideas?  Right now I rapidly press and release the go button to get started smoothly, but I imagine this rapid on-off-on-off puts extra stress on my motor.  

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Do you have some stats on the motor? Max current rating, windings resistance, max voltage, etc.

At a guess I'd say you'll only ever want the motor to go forward, not backwards, so you could make a relatively simple PWM driver to control the motor. A MOSFET or IGBT is used to vary the power fed to the motor, which is controlled by a simple microcontroller or maybe just a 555 timer, which in turn is controlled by a grip throttle or something similar.

There are lots of nice motor driver boards out there that are pre-assembled and pre-programmed, but they're probably more complex and expensive than what you need.

I have no idea what any of those terms are, but I'm busy looking them up and think I can do something like that, it seems simple enough.  Thanks for the start. 

and the motor is 500w 35v 

it sounds like the motor could have about 20 to 30 Amps current draw at a stall.

this is most definitely not a robot. :P It is attempting to break Asimov's first rule of robotics. :D

Re: variable speed.
You could build up a 555 circuit that produces pulses based on the rotation of a pot. I would not suggest you attempt to connect the output of the 555 directly to the motor, but rather, you should use a mosfet(?) controlled by the timer circuit. 

I was only slow by about 30 minutes. :)