# Max torque of Ratchet Handle

Hi All
We are thinking about securing a ratchet handle to our climber in order to stop backwards movement. The drum of our climber is a 1/2 in hex shaft. The ratchet will attach using a 1/2 in socket to the shaft and be secured to the arm. I’m having trouble understanding the maximum amount of weight our ratchet can handle before breaking. The specs of the ratchet are 649 lb-ft. How much weight can we dangle from the rope before it breaks?

You should be fine. Torque is forcedistance (your drum radius). What that spec means is that you can dangle a 694 lb robot on a 1 foot radius drum. Since you are only dangling a ~150 lb robot on a ~1 inch radius drum (allow for the rope to add width to your drum once it wraps a few times), you will only have 1/12 ft * 150 lbs = 12.5 lbft. You are well within the abilities of the ratchet.

Torque = Forcedistance. To simplify things let’s assume a 1" radius pulley. Your ratchet has a rating of 649 lb-ft. To convert to lb-in all you have to do is multiply by 12 because 1’ = 12". So, 64912=7,788 lb-in. If you want to move to a larger pulley, say 3" radius, you need to divide 7,788 by 3. Your ratchet should be fine. I hope I answered your question.

Thanks. That made sense. Is anyone else thinking of using a similar system??

We are planning on using a very similar system to yours. Ratchet and everything.:yikes:

Us too. Cheap, easy to mount, provides convenient handle for a human to backdrive the mechanism and take the robot down at the end of the match.

The Mad Scientist in me thinks we could do better, but the Pragmatic Engineer is pretty happy.

It’s important to note that if the ratchet isn’t well constrained to the hard stop you can generate a pretty serious shock load when you stop driving your winch. During lifting the drag from the ratchet is going to tend to pull the ratchet away from whatever feature you incorporate to prevent the handle from rotating. We shattered two PG71 gearboxes with about 30 degrees of rotation on a 1.5" spool with a full weight robot because we forgot to zip tie the wrench over to the side where the stop was. Ultimately, you’re probably fine, just a word of caution.