Worm gears

[MrForbes]

I was thinking about worm gears today, for a winch application for the robot, when I remembered that there are some commonly available plastic gears, that are used in garage door openers. They work with a 1/2 HP motor, so they're reasonably strong. If you search for "chamberlain gear kit" you should be able to find them for sale from several vendors for $20-30 for the illustrated set which includes some spacers, thrust washers, and lock clips.

[DonRotolo]

wow, nice find! Even comes with Grease!

That'll be used for a prototype elbow in the off season.

[MrForbes]

I have a friend who installs garage doors, thus he fixes and replaces openers too. He donated a few used gears to the team, so I got to play with them. The worm gear has two teeth, spur gear has 32, for a ratio of 16:1. Apparently it's not a steep enough ratio to prevent backdriving (he said a garage door with balance spring problems will fall closed when connected to one of the openers that uses these gears).

Still, it's a nice light weight 16:1 gearset that fits 1/2" shafts, and looks relatively easy to make a box to hold the parts.

[Jamie Kalb]

Originally Posted by squirrel

The worm gear has two teeth, spur gear has 32, for a ratio of 16:1.

How does that work? Aren't worm gears only 1 tooth gears? Or does this one have two separate threads?

[MrForbes]

There are two separate threads.

If you study the linear actuator thing in the KOP you'll see a similar screw with more than one thread.

Very strange...but that's how it is.

[Jamie Kalb]

Originally Posted by squirrel

There are two separate threads.

If you study the linear actuator thing in the KOP you'll see a similar screw with more than one thread.

Very strange...but that's how it is.

Thanks! That makes sense.

Yeah, that lead screw in the kit is just weird! I've always wondered why it has more than one thread. This year's has six, and last year's only had three (I counted ).

[Edoc'sil]

and the year before that it was 4 threads. Odd that they change it... any Ideas of were someone could obtain a cheap gear system like this that doesn't backdrive?

[MrForbes]

McMaster Carr sells a hand powered worm drive winch, perhaps you could find what company makes it and see if you can get spare parts for it? just the gears?

Some circular saws us a worm drive, for example the Skill model 77. might be some adaptable parts in that?

I've been trying to think of other things....

[sportzkrazzy]

y not use a paw and ratchet? to prevent back driving?

http://www.mcmaster.com/#gear-ratchets/=5g9esx

At the bottom.

[MrForbes]

That's what we'll probably end up doing. i doubt those stainless ones would be easy to adapt, but we might find one that is pretty easy to adapt....maybe even a part from something as simple as a ratcheting tie down strap would work? Or a socket wrench ratchet?

[sportzkrazzy]

thats what we have pretty much settled on. lol. Ur going to here a loud clanking noise we we go up but only for about 2 seconds if that lol.

[dtengineering]

If there were an FRC award for posting the most useful ideas, images and videos on Chief Delphi over the past three years, Jim, your team would have to be at the top of my list of nominees.

This is another great piece of info.

Jason

P.S. Those gears must be tough... one of my garage doors had been a bit sticky lately when it was coming down and when I checked it out, it turned out that the spring on one side had come disconnected when a fastener failed. It must have made a bang when it went, but the opener just kept chuffing right along. A quick fastener replacement (er... "UPGRADE PART" to use FRC speak) and some retensioning and it was as good as new... never missed a beat.

[MrForbes]

Thanks, Jason! We try to help where we can....

I've also learned that posting our crazy ideas here is a great way to find out quickly if we're headed in the wrong direction.

[Edoc'sil]

ya, I saw that there was a worm gear in a circ saw, ill see what i can do about finding a broken one and post its ratios and stuff.

[Gary Dillard]

Nice find. I had more or less ruled out a worm gear since they generally are extremely low efficiency (relative to a spur gear and ratchet) in order to prevent backdriving, but using a higher efficiency worm drive with a ratchet might be an option. Any idea of the efficiency of this set?