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  #31   Spotlight this post!  
Unread 22-11-2013, 00:14
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Re: Prototype transmission for potential use this year

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Originally Posted by MichaelBick View Post
192 ran worm gears and did not have any problems from what I heard. They have the nice benefit of giving you more space in the center of your robot.
They also used 4 lead worms for increased efficiency, which made them backdrivable. This let them coast to stops, and even theoretically get pushed

The other thing to keep in mind about worm gears is that most of their non-back drivability (even for 1 lead worms) comes from when they're stopped. When they're stopped, you've got a ton of force pushing the worm gear's teeth into the worm (if the output's under load), and because of the angle of the contact between the teeth, it usually can't slip. However, when the tooth surfaces are turning relative to each other, you're dealing with kinetic sliding friction, which is a lot less. You'll actually see the output pushing the input a bit when some worm gearboxes aren't under power, but moving. Because they no longer have to deal with the huge static coeficient of friction, they become essentially temporarily backdrivable. This means that worm gearboxes can coast for a little while, especially when they've got a fair amount of force on the output.
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Unread 22-11-2013, 00:30
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Re: Prototype transmission for potential use this year

That seems brilliant! Do you know how that would work? It seems quite tricky!
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Unread 22-11-2013, 01:01
MichaelBick MichaelBick is offline
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Re: Prototype transmission for potential use this year

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Originally Posted by DampRobot View Post
They also used 4 lead worms for increased efficiency, which made them backdrivable. This let them coast to stops, and even theoretically get pushed
From what I've heard they weren't backdriveable until the gears wore in, and they had no problems.
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  #34   Spotlight this post!  
Unread 22-11-2013, 10:04
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Re: Prototype transmission for potential use this year

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Originally Posted by yash101 View Post
Saneless,
This is a really great design. Is your robot an omni-drive robot? I showed this to my team captain and he seems quite interested! Also, I do not know if this has been discussed yet, but since the worm can turn the gear but the gear can't turn the worm, wouldn't the momentum of the robot cause the gears to strip? I do not see the point of worm gears because one sudden stop could possibly strip the gear!

I think that the internal braking in motors should be enough. With that high of a gear ratio, that momentum is converted into electricity and discarded as heat, casuing no damage to any physical component!
What do you mean by omni-drive? I think the answer is yes. The sudden stop I don't really think will be an issue, yes the wheels will lock up but worse case the energy will go into the robot frame and might tip the robot slightly or make the wheels just skip over carpeting before anything bad happens. It takes considerable force to strip these teeth but we will see how much of an issue it becomes. We already have several contingency plans in case it becomes an issue(such as a rubber interface as a clutch system that would slip on high force changes).

Last edited by sanelss : 22-11-2013 at 10:07.
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Unread 23-12-2013, 09:05
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Re: Prototype transmission for potential use this year

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Originally Posted by sanelss View Post
Hi sanelss,

Thanks so much for sharing the details of your design; the youtube video was terrific!

We're working on a similar design for sim motor/Jaguar/encoder control/Mecanum wheel. Here're some links that describe gear design that have been discussed in this thread:

Surface hardening and polishing of gear wear-in
Gear tooth strength
Worm gear "anti back-drive" or "self locking"

We looked at worm gear to allow getting the CIM motor 90 deg to wheel but are pursuing a 2-stage design with planetary on the wheel shaft and bevel for 90 deg transition:



Do you have advice on where to source gears? I've only found expensive sets for industrial fabrication and very cheap hobby gears.
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Unread 23-12-2013, 10:12
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Re: Prototype transmission for potential use this year

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Originally Posted by DavisDad View Post
Hi sanelss,

Thanks so much for sharing the details of your design; the youtube video was terrific!

We're working on a similar design for sim motor/Jaguar/encoder control/Mecanum wheel. Here're some links that describe gear design that have been discussed in this thread:

Surface hardening and polishing of gear wear-in
Gear tooth strength
Worm gear "anti back-drive" or "self locking"

We looked at worm gear to allow getting the CIM motor 90 deg to wheel but are pursuing a 2-stage design with planetary on the wheel shaft and bevel for 90 deg transition:



Do you have advice on where to source gears? I've only found expensive sets for industrial fabrication and very cheap hobby gears.
McMaster sells some, or you could go with one from boston gear. I've done a swerve with the L110y. They're pretty expensive.

As for the drive design, bevel gears are going to be more durable than the worm gear setup. However, you do have to take into account that the two gears will be pushing against each other in every way possible, so you'll need thrust bearings, as much support as possible on your shafts, and you should use shorter shafts to minimize bending. It's also advantageous to run the gears at a higher speed if possible. When the gears run slowly, they can bend away from each other and slip.

Also, whenever you use gears, REMEMBER TO LUBRICATE THEM!
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Unread 23-12-2013, 11:50
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Re: Prototype transmission for potential use this year

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Originally Posted by magnets View Post
McMaster sells some, or you could go with one from boston gear. I've done a swerve with the L110y...
Thanks for the feedback!

I have a couple of L93Y miter gears I bought on Amazon ($17) to play with. Our design has changed and requires a gear reduction and I'm just learning about bevel gear sets. Any guidance on bevel gear selection would be greatly appreciated.
  #38   Spotlight this post!  
Unread 23-12-2013, 18:29
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Re: Prototype transmission for potential use this year

Ok, there is a lot for me to cover here

First off, please lubricate your gears, and put some sort of cover on the gearbox so the gears don't get covered in debris. Your efficiency is already going to be really low using a two start worm and no lubrication isn't going to help.

I have to agree with many who've already stated this, you are at risk of snapping the worm gear teeth. You have the benefit of using a bigger pitch gear than we did (16 Pitch right? or metric?) but you'll also using a smaller diameter gear and bigger wheels. The gear teeth snapping was one of our main concerns and we would never have used worm gears if they didn't back drive.

As for getting the worm gear in a harder material the only other material that they're made in is cast iron and while thats harder it's also brittle and won't help at all with the teeth snapping issue.

One other comment on the design, you're going to want thrust bearings on both sides of the worm.

Quote:
Originally Posted by MichaelBick View Post
From what I've heard they weren't backdriveable until the gears wore in, and they had no problems.
Our Gearboxes were always back drivable, we could always push the robot around but it just wouldn't roll by itself early in the season. By champs we could push it and it would roll just like it would if it had a standard gearbox.

We never had any problems with the worm gearboxes, we didn't have to touch them the whole season...or after.

Quote:
Originally Posted by DavisDad View Post
Do you have advice on where to source gears? I've only found expensive sets for industrial fabrication and very cheap hobby gears.
Our worm gears were Boston gear gears's purchased through Motion Industries. Gears with the same specks are available from SDP-SI.
Boston Gear bevel gears are also available through Motion Industries but i would suggest getting Martin Sprocket and Gear gears instead. Martin bevel gears are case hardened and will last longer than the Boston gear ones.
The bevel gears on Mcmaster-carr are Martin but they have a limited selection so we bought ours through Motion Industries.
But yeah they're all pretty expensive...
  #39   Spotlight this post!  
Unread 23-12-2013, 19:00
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Re: Prototype transmission for potential use this year

Quote:
Originally Posted by Joey Milia View Post
Ok, there is a lot for me to cover here

First off, please lubricate your gears, and put some sort of cover on the gearbox so the gears don't get covered in debris. Your efficiency is already going to be really low using a two start worm and no lubrication isn't going to help.

The gear teeth snapping was one of our main concerns and we would never have used worm gears if they didn't back drive.

As for getting the worm gear in a harder material the only other material that they're made in is cast iron and while thats harder it's also brittle and won't help at all with the teeth snapping issue.

One other comment on the design, you're going to want thrust bearings on both sides of the worm.


.
I brought up a few of the several concerns here, but I don't have experience with worm gearing for drive parts. My thought is that the teeth will just snap off before the wheel looses traction with the ground. In your gearbox, did you have your worm gear before or after any other reduction?
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Unread 23-12-2013, 19:22
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Re: Prototype transmission for potential use this year

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Originally Posted by magnets View Post
I brought up a few of the several concerns here, but I don't have experience with worm gearing for drive parts. My thought is that the teeth will just snap off before the wheel looses traction with the ground. In your gearbox, did you have your worm gear before or after any other reduction?
I know you were the first one to bring up these concerns and I agree with you completely, I was just adding another voice to the argument.

In our gearbox we had a 1:1.4 spur gear (20 to 28 tooth) reduction from each of the cim motors before the 1:10 reduction of the worm gear (4 start worm and 40 tooth gear). The worm gear was on the output shaft. It can be seen here http://www.chiefdelphi.com/forums/sh...ht=192+gearbox.
The layout is the same as the AndyMark rawbox
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Unread 23-12-2013, 19:46
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Re: Prototype transmission for potential use this year

Quote:
Originally Posted by Joey Milia View Post
I know you were the first one to bring up these concerns and I agree with you completely, I was just adding another voice to the argument.

In our gearbox we had a 1:1.4 spur gear (20 to 28 tooth) reduction from each of the cim motors before the 1:10 reduction of the worm gear (4 start worm and 40 tooth gear). The worm gear was on the output shaft. It can be seen here http://www.chiefdelphi.com/forums/sh...ht=192+gearbox.
The layout is the same as the AndyMark rawbox
That's really cool. I've never seen a robot with this sort of layout. The gearbox looks pretty small/space saving. Thanks for sharing!
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Unread 24-12-2013, 00:42
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Re: Prototype transmission for potential use this year

The gear box that Joey linked to is the first generation of space saving designs that 192 has produced. This year we will be using our third generation of space saving gear box. Each year is different and this gives the students a great engineering project to work thru. The worm gear box was bulletproof.
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Last edited by Seth Mallory : 24-12-2013 at 20:52. Reason: spelling
  #43   Spotlight this post!  
Unread 24-12-2013, 05:23
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Re: Prototype transmission for potential use this year

Quote:
Originally Posted by Joey Milia View Post
Our worm gears were Boston gear gears's purchased through Motion Industries. Gears with the same specks are available from SDP-SI.
Boston Gear bevel gears are also available through Motion Industries but i would suggest getting Martin Sprocket and Gear gears instead. Martin bevel gears are case hardened and will last longer than the Boston gear ones.
The bevel gears on Mcmaster-carr are Martin but they have a limited selection so we bought ours through Motion Industries.
But yeah they're all pretty expensive...
Joey,

Thanks so much for the info! I hadn't found the Martin company; I've ordered the a Martin set: 3:1, 16P, steel/CA to test. I found them on Amazon where I've have had excellent shipping service. I use Amazon Prime and all Prime orders are free (with subscription) and guaranteed delivery dates usually within 2 days.
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Unread 24-12-2013, 15:15
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Re: Prototype transmission for potential use this year

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Originally Posted by DavisDad View Post
Joey,

Thanks so much for the info! I hadn't found the Martin company; I've ordered the a Martin set: 3:1, 16P, steel/CA to test. I found them on Amazon where I've have had excellent shipping service. I use Amazon Prime and all Prime orders are free (with subscription) and guaranteed delivery dates usually within 2 days.
Good to know they're on amazon with prime, ours took a lot longer to get to us from motion. I don't know how much info amazon gave you on the gears but all dimensions and mounting distances are available on their website in the catalogs.
This is the one for their bevel gears http://www.martinsprocket.com/docs/d...s.pdf?sfvrsn=4
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Unread 24-12-2013, 18:48
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Re: Prototype transmission for potential use this year

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Originally Posted by Joey Milia View Post
... I don't know how much info amazon gave you on the gears...[/url]
Good point! I almost wrote: Amazon's technical information is very weak and sometime flat-out incorrect. I never select from their info; only part #, and they sometime screw that up.
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