Saturday, May 29, 2010

Off and Running

The machine has gone mobile!

The previous potentiometers were a bit touchy, so I added two 1.2k ohm resistors on the steering control ground and 5v line so there's fuller range around the center. I tried the same with the speed control but that cut the speed down way too much, so that one is back to using the full range.

I added a DPDT switch to act as a neutral setting ... when thrown one way, the lines to the motor controller come from the center pickup on the potentiometers. When the switch is thrown to the other side, the motor controllers get a 2.5v signal (centering steering and throttle) derived from two equal resistors between the ground and 5v power. This sets the control input to the center, and the motors stop.

The form factor for controls is a big part of how usable they are, and my homebrew system is rough but functional. I mounted the steering control on the end of a steel can (I believe it was re-fried beans that were used for nachos) with the throttle coming out the right side and the neutral switch on the front.

I used some square 3/4" oak as levers, drilling a hole for the control, cutting a slot in one side, and drilling another small hole so a bolt and wing nut can squeeze the wood tight on the shaft. The 1/4" drill made the hole slightly loose, so I shimmed it with a bit of metal from a cat food can (thanks Robert Pirsig) and everything tightens nice and snug.

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