Ratchet control

For many robots the climb mechanism will extend to grab the bar and then retract to pull up. A ratchet is a good way to hang for the required time. I can easily envision a ratchet on a 1/2" hex drive shaft but that shaft must change direction to pull up. The ratchet direction needs to be flipped as it changes from extension to retract. Are servos strong enough to do flip a ratchet that has some load on it?

Could be a cut off wrench or a versaplanetary ratchet.

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In general, we’ve always used a different motor to do the lifting than we used to do the extending, so we’ve never run into this issue.

Remember you don’t need to prevent downward movement on the way up, you just need to not prevent upward movement. Don’t worry about disengaging a ratchet, worry about engaging it.

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I suggest looking at the Everybot… They have a ratchet attached to the climb and they also extend and retract their telescoping climber mechanism.

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If you have your cable or strap wrapped around a drum you can drive the drum until its fully unwrapped and then continue driving it the same direction to start rewrapping it

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In Steamworks we used 1/2 of a ratcheting wrench mounted to a 1" stroke pneumatic cylinder. We rounded the hex shaft for the ratchet to ride on during the match and then pulled it onto the hex to stop. It worked great

For Ri3D, we didn’t use a ratchet, and our climber worked just fine. The robot was in the 100 pound ballpark using a MiniCIM with an 81:1 reduction on our winch and a 1/2" diameter winch drum (hex shaft). While we were ready to strap a ratcheting wrench to the side of the robot, the simplicity of the system made it nice.

Definitely try to put a ratchet on if it makes you more comfortable, but overpowering your climber motor with a large reduction is always an option.

We are planning an arm to reach and pull up, not a winch. It will have pair of CIM with a reduction in the 300x range to get the needed torque and safe currents. I’m worried about stall currents being far beyond 40A and blowing fuses or burning out motors. We don’t have pneumatic yet and don’t want to put on an entire system to flip a switch on a ratchet.

To answer this specific question, no, the ratchet needs to be un-loaded to reverse. There are many ways to get around the issue of not being able to reverse your ratchet, however.

As mentioned above, Everybot uses a winch to un-spool and re-spool a winch. The shaft never has to reverse.

Here is a video of how the sequence works.

This is a miniCIM on a 50:1 versaplanetary reduction which gives enough resistance to back driving that the hook can be tensioned upwards the whole match without floating upward when crossing barriers, while still having plenty of torque to lift a heavy robot in a couple of seconds.

We used a servo last year to turn the versaplanetary ratchet for our suction climb and it worked well to lock it in. Our suction lift had to go up let the plate fall onto the platform and then down when we actually climbed on it.

Edit: I don’t think we swapping directions on our ratchet though. It went from completely disengaged to engaged.

My team has used a system before where we wound up the winch cable on our climb backwards, so that it would feed out as the winch turned, but after it ran out of cable, it started wrapping back up. That way, we just need to program a preset encoder position for the motor to target to extend the climber arm, then we can just keep pulling it after we hook on to the bar.

(I feel like this was a really sucky explanation, so feel free to ask me to clarify)

There we go. That’s the feedback I was looking for. Disengage to Engage is good for me. Time to order that versap ratchet.

You don’t mention a ratchet so yeah not sure what you are saying. Perhaps you are saying you use the encoder to tell the winch to just sit at a stationary position. When we are in that position our torque will be very high and I am afraid the motor current will blow the 40A fuse. So I’m looking at a ratchet solution to take the load off the motor.

We used a rachet so that the winch will only spin in one direction, but wrapped the cable in a way that let the climber arm extend via surgical tubing when it first started turning. Once the climber is fully extended, all of the cable on the spool has been released.

If we continue to spin the winch in the same direction, the cable will re-spool in the opposite winding.

Pretty much, it is just a way to deploy and retract a climber while only having the winch spin in one direction, so you can easily add a rachet.

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We would initially have the cable spooled counter clockwise if looking from the left side of the robot, and the spool could only spin counterclockwise, so it would release cable. After it ran out, it would start winding back up in the opposite direction. We just used the encoder feedback to make sure that it deployed to the proper height before we lined up to climb.

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Oh, now I see. Yeah, thats a good solution for a winch based climb

Yeah, I wasn’t very clear at first. The switch on the versaplanetary rachets are more to reset the robot between matches. You actually can’t get them to change modes if there is a significant amount of force on them.

Heres the images. It’s a servo connected to a rope which essentially pushes the ratcheting switch on and off. It starts in the non-ratcheting position, and then we activate the servo to push the button and engage the ratchet to stay hanging.

IMG_0843.HEIC (1.5 MB) IMG_0844.HEIC (1.2 MB)

What’s a *.HEIC file? expecting JPG or GIF…