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Kmonteith
20-01-2016, 16:37
We are trying to design a mechanism to scale the tower! We want it to lock once it reaches the top so it doesn't back drive. We can't figure out how to do this. Can any one help.
EricLeifermann
20-01-2016, 16:41
Here you go. (http://www.sears.com/ue/home/dual_ratcheting_wrench.png)
rzoeller
20-01-2016, 16:43
We are trying to design a mechanism to scale the tower! We want it to lock once it reaches the top so it doesn't back drive. We can't figure out how to do this. Can any one help.

A worm gear would do.
Chris Endres
20-01-2016, 16:43
There are several ways of doing this, one would be a ratchet and pawl mechanism:https://en.wikipedia.org/wiki/Ratchet_(device)

Another that is seen in FRC is a bike brake. This is a little more complicated, but a viable option.
EmileH
20-01-2016, 16:44
To prevent backdrive, you can use a disk or bike brake on the end of a drive shaft of an elevator that would raise/lower your robot. Team 696 used a pneumatic disk brake on their 2015 elevator (https://youtu.be/dmO8fNOSnVQ?t=4s).

EDIT: sniped
Matt C
20-01-2016, 18:14
Here you go. (http://www.sears.com/ue/home/dual_ratcheting_wrench.png)

With a hex shaft.
jnicho15
20-01-2016, 18:29
Here you go. (http://www.sears.com/ue/home/dual_ratcheting_wrench.png)

548 actually used this on our shooter winch. We had a shifting gearbox with a CIM on it pulling back nylon webbing straps. When we "shifted", it detached the motor and CIM from the winch spool, allowing the shooter ram to extend.
Anthony Galea
20-01-2016, 18:52
In 2015, we cut the teeth off of a sprocket, mounted it to a hex shaft using a hex hub, and straddled it using a pancake cylinder with pads on both sides of the sprocket to clamp down on it. We had something in the code so that if the brake was applied, there was no way the motor could revieve power to try to overpower the brake.
sanelss
20-01-2016, 19:01
A worm gear would do.

depends on the ratio but don't be fooled, worm gears can still be back driven. We use 1:16 ones and they can be back driven pretty easily and certainly wouldn't hold a robots weight. A ratchet is the better answer
MaGiC_PiKaChU
20-01-2016, 20:45
this could do the trick if you're using a rope or cable

https://www.petzl.com/sfc/servlet.shepherd/version/download/068w0000001P3IrAAK
Scott L.
21-01-2016, 19:31
https://cdn3.bigcommerce.com/s-t33k8m/products/361/images/697/karst_2268_103614852__85286.1423780889.1280.1280.j pg?c=2

I have used this to raise heavy loads up a tower. worked great :D