How to prevent backdrive on climber?

Hello, my team is using an elevator for a climber this year. It climbs very well, but it runs into a problem with backdriving, even in brake mode. We tried increasing the reduction in the gearbox to make it harder to backdrive, but a reduction high enough for that would be so slow that it wouldn’t be acceptable to us. Does anybody know how to decrease/eliminate backdrive? Thank you!

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Use a VP ratchet slice or just a ratchet wrench on the end of a hex shaft with a hard stop

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Back in the olden days of steamworks, we had a strap with velcro, and once that hooked it climbed up. To lock it, we used a cog with a paul on it, then just brought a Wrench, cranked it back a little, and lowered it down. This would work assuming your using a rope or chain of some sort

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You can try looking into the WCP friction brake. Also if you end up going down the ratchet wrench path, use a flex head wrench that way when you get your robot off of the field, you can flip the wrench away from the hard stop and it will coast down.

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If you don’t want to bother with a brake or a ratchet of any type, using constant force springs could help the system not backdrive.

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I second the 1/2" ratchet wrench. We used this method successfully during Stronghold as well as Steam Works.

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I’m surprised brake mode doesn’t hold it. If you increase you gear reduction then brake mode would work better, but that would slow your mechanism down.

The options that others have mentioned are good.

Another option would be to use a worm gear to drive your mechansim. Worm gear drives have a high resistance to back driving given the helical angle of the teeth on the worm gear. I’ve seen a worm gear gearbox on Andymark, but have no experience with them. It says you can back drive that gearbox although if you used brake mode as well, I bet it would hold with no problem.

if you guys are using pneumatics on the robot, you can have a piston to shootout some mechanism that can hold the robot from falling down. If you watch our team’s(599 robodox) robot for power up, we had a latch on top of the elevator to lock the robot into place after climbing.

The section on the climber in 2020 Everybot Build Documentation gives a good description of how they did it.

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It it’s an elevator, then the “mechanism” doesn’t have to be very complicated: Drill a hole in the first and second stage of the elevator so they line up when you want the elevator to stop. Line up your cylinder so the rod goes through both holes.

well, we used small pistons that did not have much strength to them. If you were to use strong enough piston, that is a completely viable solution.

We planned for this in 2018, but they (we went for 2 of them) didnt go on the comp bot.

  1. We didnt have the weight
  2. We didnt need them in the end

I guess our 2x 50lbs constant force springs were enough.

We used metal rods tapped on one end to screw onto the piston.

The pancake cylinder Vex sells has a 10-32 tapped hole at the end. Thunderhex shaft has a #10 thru hole. Cut a length of shaft, add a 10-32 screw, and you have a bolt robust enough to hold anything you’ll need for FRC.

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Where did you get the 50 pound springs? I’m unable to find anything stronger than 40.

Aka the 42lb yoyo katana

As a guy who made the mistake of impulsively grabbing a runaway 42lb conforce spring I advise using caution in your quest for more power.

Someone used one-way bearings one year. I can’t remember who.

I was looking for a moment at having 2 one-way bearings, where slack would come from one spool and tension would come from another on the same shaft. Only one would move at a time based on motor direction

Problem is that it is difficult to design a mechanism for that

Buy a disc brake kit off Amazon and put it somewhere inline on a hex shaft with a hex hub. The bolt patterns are close enough to mount to stock bicycle discs and you can use a pneumatic actutator to just pull on the brake cable. Easy peasy.

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Can you describe this a bit more, Ryan?

Thrifty Disc Brake?

https://www.amazon.com/BlueSunshine-Mechanical-Brake-Front-160mm/dp/B077JVRG6X/ref=mp_s_a_1_6?dchild=1&keywords=disc+brake+bicycle&qid=1579656602&sprefix=disc+brake+bi&sr=8-6

The hole pattern more or less fits with FRC’s 6 bolt hole pattern. Teams have then put them on a hex shaft at some point of their power transfer system and connect a small actuator to pull the cable on the brake caliper, causing it to lock the system up.

We rigged up something like this in our elevator on 4329 in 2015. The team was extremely COTS heavy that year so excuse the goofy inline dual versaplanetaries :slight_smile: Did a fine job holding the elevator’s position with 6 totes though -

Those are ~6" discs but there are smaller ones or you can make your own.

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