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Motorized rat advice

Old 09-30-2008, 10:51 PM
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Default Motorized rat advice

Hey everyone,

This might not be posted in the correct forum but my project seems to fall into several different areas so here goes:

I am currently researching how to build a motorized rat for a stage production (the Nutcracker). I have been using one for the past 6 years which consisted of an electric rc car with a rat body attached to the top replacing the car body. All it was able to do is 'drive' around the stage. It worked but needless to say, not very realistic! I would prefer NOT to use it again this year!

My goal is to build one which would do the following:
1. Move around the stage with a speed range of a "crawl" to 15 mph. (The stage is flat with a vinyl surface.)
2. Stop on centerstage and "sit up" quickly; turn its head left to right; and lay back down to its crawl position.
3. Have simple red eyes light up.
4. Have a tail which would "wag".

Each one of my goals presents a design discussion. I have several ideas for each but would love to have your input. Also, even though I have ideas I have very little knowledge to implement those ideas. I have been researching motors, servos, transmitters, receivers, esc's and such, but I am a bit overloaded! Everything RC seems to be geared toward cars, trucks, planes, and helos. I think these products can be used for my application but was hoping for some advice.

If any of you are up for helping out a newbie please start any discussion. (You'll also help several thousand audience members!!!)

Old 07-04-2009, 10:42 PM
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Default RE: Motorized rat advice

I'm a cybernetics/robotics engineerwho uses RC machinery to power my devices. I can tell you your rat will be quite large judging by what you want from it (maybe even as big as the car you specified), and here is what I would do in your position.

Your controller will be a 4-channel device, with its channels dedicated to the following:

Channel 1:Left side motor
Channel 2: Right side motor (the purpose for two independant motors is so you can steer it, one motor with a steering servo would be unconventional for the realism you want.
Channel 3: Servo - For sitting up
Channel 4: Servo - For turning head left and right

As for the motors, it may even be a better idea to rig a pair of servos for continuous rotation to save space, but Ican garuntee that they won't hit 15mph.

While on that, 15mph may be a little bit unreasonable, even for motors. At those speeds and the probable weight of the vehicle will make it flip over when it turns. If this is simply for a stage production, you may want 5ish mph. (brisk walking speed)

The red eyes would be jury-rigged onto the battery before the line hits the ESC, same with the tail, except the tail will require a small IC board to control the wagging motor to within your specified params. This probably may not be worth the effort in the end, since an IC board could take up a lot of internal space and the tail may only be viewable by a few select rows of audience. IMO a pipe cleaner holding up the tail would much easier, and it would bobble back and forth when the rat accelerates and stops.

On a final note; don't expect this to cost less than $100, I predict that it may cost upwards of 200-400 if you don't have some of the materials already.

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