Subject:
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interfacing to RC cars
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Wed, 1 Jan 1997 21:09:44 GMT
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Original-From:
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Randy Sargent <RSARGENT@NEWTONLABSspamless.COM>
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Viewed:
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1481 times
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I haven't interfaced RC cars to a handyboard, but my experience might help
anyway.
> 1. What type of vehicle did you use?
Tyco "Fast Traxx" and a look-alike made by Nikko. Both have dual treads
(and therefore differential steering). Both are very fast. Unfortunately,
both are discontinued, although there are plenty of other vehicles which
have differential steering. Toys R Us seems to be a good place to look.
I like differential steering because it lets you spin in place (zero
turning radius). Dealing with front wheels that turn means you have a
non-zero turning radius, which generally requires a lot more intelligence
and information about your environment.
> 2. How did you handle the steering servo with your handy board?
There's no steering "servo" motor, but instead two drive motors, one for
each tread.
> 3. How did you handle the driving motor with your handy board (did you
> use the speed controller that came with it or did you do something
> different and what)?
In both cases, I found TTL-level signals driving the car's built-in
H-bridge. I cut the traces going to the RC receiver hardware, and hooked
up through small (100 ohm) resistors to digital outputs from the controller
board. (The 100 ohm resistors are a poor man's isolation circuit). Be
sure to hook up the grounds in some fashion -- you might be able to get
away with isolating grounds also through a 100 ohm resistor, or a 1uH
inductor.
> 4. Did you use the 9V 1400mA battery pack and if so how did you connect it?
No. I used two sets of batteries.
Chuck McManis wrote:
> In general converting RC cars (and tanks) has three issues:
> ...
> 2) Slowing them down (they are designed for 9 yr olds who
> think the faster they are the better they are.)
> ...
The speed at which you can control a vehicle depends a lot on how good your
sensing is. By strapping a high-powered vision system on one of these
cars, we were able to make something which followed targets faster and more
accurately than human drivers. (you can see a picture at our web site --
http://www.newtonlabs.com/).
If, however, you're using phototransistors and bump sensors to follow lines
or walls, you'll want to slow down the car. This is hard: the cars aren't
geared down very much, so you'll find that it's very hard to run the car
at, say, 1/3 speed. You're much more likely to either stall or go much
faster. You can do a good job of slowing down the car if you have some
sort of feedback on how fast you're going, which can be done several ways
(encoders, measuring motor back EMF, etc).
-- Randy
----------------------------------------------------------------
Randy Sargent Newton Research Labs
Senior Design Engineer Robotic Systems and Software
rsargent@newtonlabs.com http://www.newtonlabs.com/
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