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.
wow, nice find! Even comes with Grease!
That’ll be used for a prototype elbow in the off season.
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.
How does that work? Aren’t worm gears only 1 tooth gears? Or does this one have two separate threads?
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 :p).
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?
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…
y not use a paw and ratchet? to prevent back driving?
At the bottom.
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?
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.
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.
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.
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.
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?
We used that exact gear set for our winch in 2004 (Frenzy)
We were very pleased with the results. Lasted 2 regionals with no significant wear.
If it is possible to back-drive it, one robot is not nearly enough force to do it in our experience. If you were lifting 2 or 3 I suppose you’d have to try it to find out.
Worm gears are fraught with peril for FIRST teams.
Well, actually, they are fraught with peril for any application, but some times you need to face your demons!
In one off applications like FIRST robots, you really need to know what you are doing to use a worm gear (other than the one in the window motors of course).
Getting the center distances right is a harder task, managing the thrust loads, etc. etc. And don’t get me STARTED on efficiency (you flush half to 2 thirds of your power right down the drain – and that is if you do things right you can waste 90% easily without even trying! But… that is is why they are not backdrivable - so that can be a plus but…)
My advice: find another way if you can.
As for me and my house… …I am thinking this is a job for NBD – Nothing but Dewalts – Worked for me and Chief Delphi in Raising the Bar, I don’t see why it shouldn’t work for Breakaway
Joe J.
We used and box end ratchet wrench in 2007 to make our lift winch non-backdrivable.
All it required was a hex of the appropriate size welded to the winch shaft, and then prodding the pawl with an allen wrench to let it back down.
worked like a charm
It appears the door opener gears probably have better efficiency than most worm gears, because they don’t have a very steep ratio, and apparently are backdriveable. The sliding tooth contact is not as efficient as the mostly direct contact of spur gears, so the efficiency must be less, thanks for pointing that out.
As for me and my house… …I am thinking this is a job for NBD
We had some fun with DeWalts our rookie year, and are a bit leary of them. I suppose if you are good at machining an 8mm hole in a pressed metal gear that has a 9mm minor diameter, then can get the gears pressed on the shafts (and have it survive a few regionals) without breaking they are OK, but that shaft to gear coupling problem makes me shy away from them for use with a CIM. A FP driving them should not be so bad.
Thanks for the comments!
My experience is nearly universally positive. The shifters have had some problems (mostly due to programming issues that put them out of gear in autonomous) but other than that, I have been very happy with them.
Of course, I have always had access to either a good wire EDM source or a retired tool & die maker that made jewelry (figuratively) so getting things made were never an issue.
AndyMark (and to a lesser extent Banebots) has pretty much put me out of the NBD business, BUT… …for an efficient high ratio (roughly 50:1) with a non backdriveable output, it is tough to beat it. imho.
Joe J.