Worm Gear Gearbox

[Peter Matteson]

The worms we used last year were 35:1 on the back of another transmission. I don't recall the ratio for the Bosch tranny we used however. We wanted an extremely high torque setup for our application though.

Pete

[Pat Roche]

Originally Posted by Dr.Bot

I did this as an experiment using the plastic gearboxes, shafts and axels suplied by first and purchased gears - there is a post somewhere of someone else who did this. The Chippawa moters fed into this I think it was a 30 fold reduction - so the speed was about 4fps. So comparable to a Fischer Price, but much more powerful, Unfortunately my entire robot platform was thrown out in a fit of spring cleaning - the gears cost about 300 bucks for two sets.

I had some pictures, put heck if I can find them.

SO worm gears will work, and you can make the transmissions with just a good drill press if you are carefull and precise.

I got the gears from "Boston Gear"

worm GH1076RH gear G1071RH

Boston gear also produces stock worm drive gear boxes, they're really efficient for worm drives and are quite heavy duty. we used one in our drive train last year and it worked beautiful. Picture Here. I beleive these were a 20 to 1 reduction and these had no backdrive.

-Pat

[dddriveman]

Originally Posted by Pat Roche

Boston gear also produces stock worm drive gear boxes, they're really efficient for worm drives and are quite heavy duty. we used one in our drive train last year and it worked beautiful. Picture Here. I beleive these were a 20 to 1 reduction and these had no backdrive.

-Pat

I did not think that you could buy gearboxes. I was under the impresion that you could only manufacturing them. Plus what is the fun in using premanufactured gearboxes, you dont even get the headaches or any of the flesh wounds that come with designing and building a custom gearbox. That is what makes it fun or at least when it is all over.

[Jaine Perotti]

Originally Posted by dddriveman

I did not think that you could buy gearboxes. I was under the impresion that you could only manufacturing them.

Yes, you can buy gearboxes. Here is a well known example.

Plus what is the fun in using premanufactured gearboxes, you dont even get the headaches or any of the flesh wounds that come with designing and building a custom gearbox. That is what makes it fun or at least when it is all over.

This is really up to the needs and opinions of each individual team.

If they feel that a purchased gearbox will meet their needs better than one that they designed and built themselves, then they should by all means go for it.

If they feel that they want the experience of designing and building their own, and have a unique design that they feel would meet their needs, then they should go ahead and do it.

The decision to buy or build is a matter of what each team feels is best for them.

For more thoughts on the matter... this thread.

-- Jaine

[Kevin Sevcik]

Originally Posted by dddriveman

I did not think that you could buy gearboxes. I was under the impresion that you could only manufacturing them. Plus what is the fun in using premanufactured gearboxes, you dont even get the headaches or any of the flesh wounds that come with designing and building a custom gearbox. That is what makes it fun or at least when it is all over.

For the most part, you can use whatever you can buy off the shelf, mechanically. So gearboxes are perfectly legal as long as they aren't custom made. Viz. AndyMark

Most people talk about building gearboxes for custom functions that an off the shelf one wouldn't fit for, or more commonly for a shifting transmisson that is difficult and expensive to obtain off the shelf. Or was, at any rate. See: Nothing But Dewalts

[Peter Matteson]

In the case of off the shelf worm gear transmission, aka speed reducers, a COTS part is much heavier than a custom one. My experience with these is that they designed for heavy machinery and not the applications that we have.

One of the best off the shelf transmission choices 177 has made in the last few years was to get the trailer jack the chip was designed for and use that to power our shoulder in 2003. There are lots of good Commercial Off The Shelf parts if you know where to look.

[OneAngryDaisy]

341 used a worm gear gearbox last year- we had a CIM geared down to match the drill motor on both sides, she wasn't as fast as we would have liked her to be (efficiency loss), but the entire year we never got pushed once- many times we met teams with much more powerful transmissions and they couldn't budge us, our frame got really beat up from that

but seeing as our main strategy was to hang quickly from the ground, winch up to the platform, and move back and forth on the platform, it was nice to know nobody could push us.

I personally am a fan of the multi-speed gearboxes over this worm gear gearbox, but if there was ever a game where you want to be a unmovable rock, like if you have to guard something, this gearbox is your man.

[dddriveman]

Originally Posted by OneAngryDaisy

341 used a worm gear gearbox last year- we had a CIM geared down to match the drill motor on both sides, she wasn't as fast as we would have liked her to be (efficiency loss), but the entire year we never got pushed once- many times we met teams with much more powerful transmissions and they couldn't budge us, our frame got really beat up from that

but seeing as our main strategy was to hang quickly from the ground, winch up to the platform, and move back and forth on the platform, it was nice to know nobody could push us.

I personally am a fan of the multi-speed gearboxes over this worm gear gearbox, but if there was ever a game where you want to be a unmovable rock, like if you have to guard something, this gearbox is your man.

Maybe this years game will give us a reason to produce a gearbox with wormgears. I would get no greater satisfaction out of life than watching another bot try to push us around.

[Max Lobovsky]

Does anybody have any links to information for calculating worm gear strength?

[Peter Matteson]

Originally Posted by Max Lobovsky

Does anybody have any links to information for calculating worm gear strength?

Do you mean strength of the gear teeth or force that you can generate with a worm gear?

[Max Lobovsky]

What are "starts"? The number of threads? I thought the number of threads was equivalent to the number of teeth so more threads is less reduction (and i would assume more efficient)

[Jizvonius]

Originally Posted by Max Lobovsky

What are "starts"? The number of threads? I thought the number of threads was equivalent to the number of teeth so more threads is less reduction (and i would assume more efficient)

If you look at the side of the worm, you should see the places where thread starts, that's a "start". The number of starts will change the gear ratio. i refer you to Paul's post.

Originally Posted by Paul Copioli

Remember, gear ratio for a worm gear is # of teeth on the gear divided by number of thread starts on the worm.

[Bacchus]

Yes, you are correct. I got just about everything back wards. In an attempt to make up for it, Here is a decent link that some pretty good info on worms... http://www.bostongear.com/pdf/gear_theory.pdf Pages 13 and 14

[Andy Baker]

Originally Posted by Max Lobovsky

What are "starts"? The number of threads? I thought the number of threads was equivalent to the number of teeth so more threads is less reduction (and i would assume more efficient)

Here is a product manual from Martin Spocket and Gear. On page 69 of this link, the worm gear has 1 start (a single thread). On page 70, it shows a worm gear with 2 starts (double thread). On page 71, a worm gear with 4 starts (quadruple thread) is shown.

On the shoulder joint of our elbow for last year's TechnoKat robot, we used a 40 tooth worm gear (Martin # W1240) and a single threaded worm gear (Martin # WG12).

This design worked well, except when the arm would bounce or hit something. The teeth on the worm gear would shear. If we ever need to use this sort gearing again for an arm, we will need to do two things: 1. use a gear with larger teeth 2. provide more of a counterbalance for this same sort of joint

Andy B.

[Jizvonius]

Originally Posted by Max Lobovsky

Does anybody have any links to information for calculating worm gear strength?

Depending on where you get them, the company will supply that information. However, if they don't, and you know the material and the thickness of the teeth, you can probably get an estimate by calculating from yield stress in shear from the material properties (look these up). The number won't be exact but with a good safety factor (which you need anyway) you should be able to meet your design needs. Use a larger safety factor if you do the calculations yourself though (your number will probably be less accurate).

*make sure you get the correct material properties as different treatments can change properties(case hardening etc.)