Quote:
Originally Posted by Gearheads1
We're testing bungee cords, which look like they'll do well and are experimenting with the window motor that seems to work well...but...anybody want to talk about how they're building some type of clutch so you don't backdrive the motor. We're talking about putting the winch on some pillow block bearings and then pulling the assembly off the window motor interface with pneumatics or another motor.
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A Ratchet plus a Dog Clutch is one common solution. The ratchet holds it when the dog clutch disengages the motor. Release the ratchet to fire it.
The problem comes in finding a simple and cheap dog clutch mechanism, for FIRST purposes.
Two years ago (2008 "Overdrive"), as a robot inspector I saw a NEAT nearly-COTS method for shooting the medicine ball, that solved it. The team hacked a stock AndyMark two speed transmission to turn it into a "string winch". They simply REMOVED the gears for high speed, and added a drum. Now, low speed winds the drum. When you shift to high, due to the missing gears it "clutches" and releases tension. It was a nice, compact, ELEGANT bolt-on winch solution, mostly made from COTS parts.
Now I admit two-speed transmissions aren't CHEAP, and if you DO have machining capacity you may be able to find a more elegant, simpler, or cheaper solution. But I felt this was one POSSIBLE answer, especially for teams with cash but without very much machining capacity available at their build site.
SOMEWHERE in the system, you'll still need to add a couple more things:
A) A ratchet or gate latch, to hold tension once wound. (You must NOT keep the motor "stalled"!)
B) Feedback (a limit switch or potentiometer), to detect "Fully Wound" or Latched, so the computer knows WHEN to kill the motor. (IMHO drivers are too busy to be forced to worry about this, and limit switches are simple and effective.)
If the ratchet (or gate latch) is independent of the transmission, you also need a release device for it, such as a cylinder or servo.
Now if you can find a way to include the ratchet on the low speed shaft (like they did), then you only need to "switch to high" (aka "clutched") to release it. More compact, but it MAY require a BIT of machining (eg a longer replacement low speed shaft, add "stuff" to the middle of the shaft, etc.)
Good luck! Please let us know what you finally used as a clutch! (Hey... We need a simple, inexpensive COTS Clutch Vendor!)
- Keith