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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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The RC-Servo Pulse to PWM conversion is relatively easy to do with a simple microprocessor setup,
The PicAxe's or the Ateml AVR Micro used in the IBC and OSMC will do it for about $15, the not so easy part is keeping the Micro running reliably in the typical combat robot environment, surrounded by crawshes, bangs, Radio Noise, Huge Electrical Spikes, and a wildly varying power supply as the batteries struggle with the load of the drive being stalled several times a second in a ramming match.
Once you have the brains sorted out, the *Really* hard part to go is to get the Mosfet H-Bridge Power-side of the circuit to survive.
The difference between pushing a baby-motor powered hobbyist robot along the floor at a leisurely pace chasing the cat and the sort of pounding a combat robots speed controller has to endure is like asking a Diahatsu to win a demolition derby.
To deal with the sort of current surges a combat bot does, the Mosfets have to be top-shelf (very low resistance) units, and the gates have to be driven with perfection, timing and power wise. Anything else will guarantee frustration as the magic smoke escapes again and again.
All the details for the IBC / OSMC style design are available for free on the net (look at the IBC manual on the RoboWars page for the schematic or the OSMC documentation here - http://www.robotpower.com/downloads/ ,
but as someone who has done it, and pointed out by Philip, I can assure you you will *not* save money trying to do it yourself.. Unless you want to spend a *lot* of time and burnt parts learning the art of power-electronic motor control, your best course is to buy a proven speed control. It only takes your home-brew to fail once in combat and you will likely suffer more damage than you would have spent buying a good one.
The "Electronize" controllers are about the cheapest proven combo, and the IBC is about the simplest to use.
The Bob Blick designs arent even in the ball park for combat bot use. No Failsafe, the H-Bridge uses Transistors rather than Mosfets which makes it far too wimpy to handle combat power motors, and the analog servo-pwm conversion is finicky and drifts around.
If you really want to build your own, read up on the OSMC documention link above. _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
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Mon Apr 03, 2006 12:55 pm |
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