Torque Rating

[yarudl]

I'm looking at gearsets and I came across a set that doesn't have a torque rating listed. Does anyone know how much torque the worm gears on mcmaster-carr can handle?

[IKE]

Post some part numbers, and we can see if we can give you a hand.

If you are looking for a good worm gear box, may I recommend looking at these:
http://www.andymark.com/product-p/am-0917.htm

[Cal578]

Post some part numbers, and we can see if we can give you a hand.

If you are looking for a good worm gear box, may I recommend looking at these:
http://www.andymark.com/product-p/am-0917.htm

We're looking at McMaster-Carr worm drive (http://www.mcmaster.com/#standard-gears/=l5rmo1):
Worm (screw) 57545K527
Worm gear 57545K515
These are 12 pitch, 14.5 degree pressure angle, cast iron, and would give a reduction of 30:1.

The am-0917 ("http://www.andymark.com/product-p/am-0917.htm) has impressive ratings for plastic gears. If I read the drawing correctly, it looks like it can only attach to 1 CIM motor. We were hoping to use two.

[FrankJ]

Seat of the pants say you will not break the Mcmaster Carr gear sets with any first legal motor. The issue is worm gears have sliding friction. Under high loads, this can really be significant. The more you load them up the better the lubrication needs to be.

[MrForbes]

The am-0917 ("http://www.andymark.com/product-p/am-0917.htm) has impressive ratings for plastic gears. If I read the drawing correctly, it looks like it can only attach to 1 CIM motor. We were hoping to use two.

If you can use two of these gearboxes, then you can use two motors.

[IKE]

Here are some example calcs that should help you rate the cluster you are looking at:
http://cr4.globalspec.com/thread/11025/Worm-Gear-Calculations

here is a link with better/more in depth calculations:
http://www.roymech.co.uk/Useful_Tables/Drive/Worm_Gears.html

[Gregor]

Post some part numbers, and we can see if we can give you a hand.

If you are looking for a good worm gear box, may I recommend looking at these:
http://www.andymark.com/product-p/am-0917.htm

Problem is these have been out of stock since at least last week, when I first checked.

[MrForbes]

Make your own...you can buy the gear set at places that sell replacement parts for Chamberlain garage door openers.

[IKE]

This is heavy, and inefficient, but it is cheap, and is pretty durable:

http://www.harborfreight.com/2000-lb-capacity-geared-winch-5798.html

it is also a 40:1

[yarudl]

So after contacting McMaster I did get a response on the torque ratings. This is what I got: http://i.imgur.com/tColPax.png It's a little blurry but it says at 1800 RPM it can take 340 in lbs of torque.

[Spirator]

You'd be able to lead them up to the material's yield strength. Most of the force on a worm gear would come from force along it's axis coming from the backdriving of the output gear which would be one mode of failure. As previously mentioned with a heavily loaded gearset, you'd also encounter a lot of friction and this would cause your motors to work harder so make sure you lubricate those gears!

The wormbox is made of nylon and while nylon will yield at less stress than steel, it wears less and a nylon gearset will also have less friction. In this application where you're unsure whether or not your gearset will hold up under loading, you may consider it safe to go with the McMaster parts.

As for a more direct answer, it's difficult to calculate how much torque they can withstand without detailed calculations. The 57545K527 worm is made of steel and it should be able to handle the loads fine. If you have doubts, I'd recommend to fail early and fail fast, or just email McMaster Carr asking.

Edit: I see you already emailed them! Fantastic. 340 in*lb or ~38.41 N*m isn't that much. How much load are you placing on the output of the gearbox?

[yarudl]

You'd be able to lead them up to the material's yield strength. Most of the force on a worm gear would come from force along it's axis coming from the backdriving of the output gear which would be one mode of failure. As previously mentioned with a heavily loaded gearset, you'd also encounter a lot of friction and this would cause your motors to work harder so make sure you lubricate those gears!

The wormbox is made of nylon and while nylon will yield at less stress than steel, it wears less and a nylon gearset will also have less friction. In this application where you're unsure whether or not your gearset will hold up under loading, you may consider it safe to go with the McMaster parts.

As for a more direct answer, it's difficult to calculate how much torque they can withstand without detailed calculations. The 57545K527 worm is made of steel and it should be able to handle the loads fine. If you have doubts, I'd recommend to fail early and fail fast, or just email McMaster Carr asking.

Edit: I see you already emailed them! Fantastic. 340 in*lb or ~38.41 N*m isn't that much. How much load are you placing on the output of the gearbox?

We're having the whole robot on a pulley connected to this. so about 170 in-lbs.

[Spirator]

Where did you get the 170 in-lb figure from? What's your pulley diameter and how much load are you lifting?

[yarudl]

We're using a 2" diameter pulley and it's lifting the weight of the robot. We overestimated the load to be safe.