Winch ratchet and pawl design
 

This last season as I wandered around the pits I saw some really interesting winch designs. I figured I'd share the winch we used this year. During the design phase we looked at purchasing and modify a ratchet and pawl from McMaster. I know some teams did this. After some discussion on time we decided to design our own. We opted for a fairly large and open ratchet, similar to what you'd have on a barbed wire ratchet tensioner. Yes, we even thought about modifying on of them.

It turned out to be easy to make and was reliable. The dimensions were estimated by winding our paracord onto a spool and measuring it. I turned the hub at work as lathe tooling at the school is limited. One of only a few parts that weren't done at the school by students.

We used a hex drive gear reduction and the hex bearing for the outboard support.

I'd be interested to see some other designs if you have something to share. Some teams had winch issues so I hope this helps someone.

Here is the design. 3" in diameter and 1.75" inches wide.


Turned blank.


Milling the ratchet. This is a first year student. He setup the job on the mill and ran it.


Hex broaching on the old press in the AG shop... but it's all they have.


Here's the completed winch. For some reason I didn't get any better photos.

Re: Winch ratchet and paw design
 

We managed to get away with 3D printing our ratchets this year. As it turns out, 3D printed parts work great when there's something weaker to give in. We had no issues with 1/8th in Polycarbonate ratchets until the final match of our 2nd regional, but the issues managed to follow us all the way to a post-season demonstration.

Sorry about those delays between Einstein matches.

Re: Winch ratchet and pawl design
 

That is good to know. We discussed 3D printing the winch but had our reservations. As it was some were concerned about using aluminum for the ratchet. In the end the concerns were unfounded. Do you have a photo of your ratchets?

Re: Winch ratchet and pawl design
 

https://www.instagram.com/p/BCl9-Dgj...=330_beachbots

The picture doesn't show the other side (there's a hub to interface with the PVC pipe we used as a winch) but it gives an idea of the tooth profile.
Raytheon printed them in Stratasys Ultem as a donation.
Assuming that they were printed completely solid, they would cost an upwards of $100 in material to produce. (each)

Re: Winch ratchet and paw design
 

We've used 5160A5 and 5163A16 from mcmaster as a ratchet and have been very happy both times.

Super easy to use.

Re: Winch ratchet and paw design
 

696 has laser, plasma, and water jet cut ratchets in 2013 and 2016. There might be a picture somewhere on our 2016 build blog.

Re: Winch ratchet and paw design
 

We used a ratcheting wrench for our climber in 2016 and loved it. Simple, cheap, and already interfaces with a hex shaft. The reversible ones let you unspool the winch easily too. If we need a ratchet in the future, a wrench will likely be involved.

I like seeing all of the winch systems that teams come up with, but they tend to be a bit overkill. Winches that have a large reduction from the motor, but also a large diameter spool have always bugged me. The one in the OP doesn't have the large spool problem, it looks like a nice lightweight winch pulley.


For the milling operation pictured, is there a reason you're using a plywood support piece instead of just bolting the pulley to the table? We're getting more involved with milling, just looking for tricks we don't know about.

Re: Winch ratchet and pawl design
 

I like the wrench idea. I've seen a few other team use them. Not sure how we missed something so obvious in hindsight. The design and building of the ratchet and pawl made it worth it for the experience in my opinion.

The wood... you wouldn't normally do that except the stud we had was too long. The school doesn't have a very good selection of parallels or fixturing hardware. In the end it worked and the wood protected the finish. :p

Re: Winch ratchet and pawl design
 

I am in a similar situation at home with the lack of fixturing hardware. This is a great idea!

Re: Winch ratchet and paw design
 

In 2014 for our choo-choo we used layered sheet metal to create our ratchet and pawl. Basically you just make several from thinner laser cut sheet metal and bolt the lot together. Not as strong as a solid part but way more than strong enough. We used 3/16" stainless steel with 4 layers to form our ratchet. We have done this with medium duty, high and low speed gears with great success from mild steel and aluminum.

Re: Winch ratchet and paw design
 

While we never built it, one of our 2015 strap winch designs had a 2-3" diameter pulley that required lower gearing than if we'd made it half size. The reason? We needed just as much force at the end of the winching as at the beginning. The larger spool that required fewer wraps would have provided a better match of motor torque and speed to the load than a smaller one, and better linearity.



Back to OP -- what is the purpose of the hole to the left of the hex bore in the first render? At first, I thought it was for the secured end of the cord, but as I looked for a better location (not under the torque support area for one of the teeth), I realized that the cord should be threaded through the non-pawled side of the pulley to reduce the chance of fouling the pawl. Looking at the last image of the OP, it appears that the cord passes through the left (non-pawl) side. So what is that hole?

Re: Winch ratchet and pawl design
 

The ratchet and pawl was originally designed on the outboard side. After the spool was done, minus the counter bore, it was fitted to the motor and the designer realized the spool should be flipped. It was an ah-ha moment. The pawl mounted on the motor mount simplified everything. You'd think the easiest solution would be found in the design phase but sometimes the obvious things are missed.