The year when we had to balance our robot kept tripping the 60a breaker. After several trips over the bridge, our robot wouldnt work when the bridge came down. We found out that the circuit breakers would trip when something hard smashed into the robot. SO what we did was mount the breaker with surgical tubing!
Let’s set the “cooling the breaker” thing aside for a bit…
What ELSE to you do DESIGN wise to keep from overloading the electrical system?
Examples:
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Do you have a AHL legal slip/breakaway clutch design? Please describe it!
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Ever done anything funny in drivetrain or software design to avoid stall currents, especially when expecting Tug of War situations? (Ex’s: Enable/disable [PWM-like] algorithims to “jerk” your machine? Deliberately adding backlash or an elastic element in the drivetrain so the motor gets a “running start” when reversing?)
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Four wheel drive users WITHOUT wheel turning: How are you making “holonomic wheels”? (A tire that slips sideways easily to keep turn scrubbing forces from blowing the breakers, while maintaining good forward/backward traction.)
Please, let’s hear some DESIGN methods to avoid breaker tripping, in addition to “cooling tricks”…
Thanks!
- Keith
I’m not sure if it does a whole lot for current draw but we put a deadband in our drive joysticks. For the first bit of motion in the positive or negative Y axis directions, no signal would be sent to the PWMs. This was more to prevent strain on the drive componenets but it may have done something for current draw.
Other teams I think had a sort of “soft-power” system where power to the motors came on slowly rather than all at once. However, I am not a programmer so I don’t know how that works.
*Originally posted by sanddrag *
**Other teams I think had a sort of “soft-power” system where power to the motors came on slowly rather than all at once. However, I am not a programmer so I don’t know how that works. **
That’s a “low pass filter” algorithm, an excellent way to prevent sudden spikes in the power. However, the driver deep down must ACCEPT that filtering.
Last year we tried filtering, but it became an unconscious “war” between our programmer and our driver! <chuckle> Each upped their effects, until the robot was sluggish and the driver started slamming the sticks like buttons. They were BOTH bound and determined to get a specific behavior out of the robot, and they didn’t agree on what that was! I even started fearing for the sticks’ survival, and we didn’t have any spares! :eek:
I finally asked for ALL the filters to be ripped out of the code, and pleaded with the driver to “try not to break the robot too often” with the controls… 
The robot worked fine, AND the code was simpler.
Anyone have better luck with filters?
Anyone have any OTHER good subroutines for breaker protection that work well DESPITE an “insistent driver”?
Has anyone found software “load shedding” to be useful, i.e. locking out the compressor or other “lower priority loads” whenever the drivetrain demands a panic boost? (“Scotty, we need more power for the warp drives!!!” 
)
- Keith
*Originally posted by kmcclary *
**3) Four wheel drive users WITHOUT wheel turning: How are you making “holonomic wheels”? (A tire that slips sideways easily to keep turn scrubbing forces from blowing the breakers, while maintaining good forward/backward traction.)
- Keith **
I believe that you would be talking about Omni-Wheels. There are numerous threads about these. I am not sure exactly what they were called, but they should be fairly easy to find. There are also wuite a few pics in the 2002 robots gallery of teams Omni-Wheels
For various reasons, current draw being one of them, our '00 bot used a 6 wheel drive. In this setup, all 6 wheels are powered, where the middle two wheels are set about a quarter of an inch lower then the 4 corner wheels. This allowed us good climibing on the ramp (the primary reason for the 6 wheels) but also reduced scrubbing drasticly when turning.
Of course, having 6 wheels is more expensive (wieght, build time, repairs) then 4, in our case it was a fabulous solution. If you plan on lifiting loads while acending inclines, it’s perfect. Also, if you can get away with a two wheel drive, Why not? The bot turns faster and uses less current, the drive line is far more simple to make and repair, and probably most important, is lighter! Naturaly, using 6 or 2 wheel drives creates all sorts of problems, but its all a trade off.
-Andy A.
*Originally posted by Andy A. *
For various reasons, current draw being one of them, our '00 bot used a 6 wheel drive. In this setup, all 6 wheels are powered, where the middle two wheels are set about a quarter of an inch lower then the 4 corner wheels. This allowed us good climbing on the ramp (the primary reason for the 6 wheels) but also reduced scrubbing drastically when turning.
An excellent idea…
OOC, Were the wheels evenly spaced, or was the center pair nearer to one end? How was weight distributed across the wheel pairs? Did your robot rock back and forth between the outer sets of wheels when you reversed, and then run on the “back” (outer) pair each way?
- Keith
*Originally posted by Cory *
**I believe that you would be talking about Omni-Wheels. There are numerous threads about these. I am not sure exactly what they were called, but they should be fairly easy to find. There are also quite a few pics in the 2002 robots gallery of teams Omni-Wheels **
I’ll go check those out. Holonomic drives are pretty cool… Thanks!
BTW… Omni-Wheels are only ONE way of doing a sideslip wheel. It doesn’t have to be VERY slippery side to side, only significantly MORE slippery, enough to manage the turn scrubbing forces without sacrificing too much forward and back drive traction.
Another simpler example than homebrew Omni-Wheels might be treads made from repeated slices of inverted U channel bolted to your wheel or tread. If the inverted U can be seen looking at the side of the robot (align from side to side), AND the side to bottom edges of the vertical pieces have a radius on them (rounded, so it looks like a “U” from the front), it makes for good claw traction forward and back, yet acts like a sled runner if shoved sideways. Any slide push causes it to “climb the carpet nap” and slide easily.
Any other SIMPLE methods of making “side slip wheels”?
Remember, this thread is about ANY technique to reduce breaker blowing. Not just wheels, chilling, etc…
- Keith