Hello, I am new to gearboxes and everything associated with them. I was wondering if it is possible to take the big 3" CIM motor and make, well essentially, a worm gear to use on a pivot arm, allowing the arm to stay in the position it was rotated to.
Quite easily, as long as ou have the worm and a worm gear. Bore out the worm to 8 mm and them fasten it somehow to the CIM shaft, either pins through or a key way. If the gear reduction still is not enouph, try a initial gear reduction with spur gears. Hope this helps.
Yes, it would work.
This isn’t exactly a worm gear on another gear but a somewhat similar application:
Frog Force (Team 503) used this concept on the their robot in 2005 and said they were quite happy with it. It seemed to work really well. Take a look at this picture:
http://www.chiefdelphi.com/forums/showthread.php?t=37815&highlight=503
You can see the black worm gear shaft going down to the base of their robot under the arm. The CIM motor was mounted on the arm and is visible towards the top of the mast.
We used a worm gear on our shoulder for this year’s robot. Although we used a globe motor instead of a CIM, the gearbox can easily be adapted to fit the shaft. Here’s an Inventor rendering of it: http://static.sigmacat108.com/images/robot/shoulder_transmission2.jpg
And the actual thing:
http://static.sigmacat108.com/images/divisions/mechanical.jpg
-No L
And remember, the worm wheel induces an axial load on the worm screw and shaft, so, make sure to use bearings that can handle that sort of (axial/thrust) loading on the worm screw shaft.
As Sanddrag pointed out, the Chalupa motors cannot handle this kind of load without some help from external bearings. Side loads on these motors require significant (near stall) currents. The same thing can be said for unsupported sprockets and chains.
so should I buy a worm gear from McMaster-Carr? We would be using it to turn an arm about 270 degrees and will way maybe 15 pounds. As I said, I’m new to this. Thanks.
Ha! Or not… Getting the necessary accuracy and tolerances will be very difficult and I would not recommend barreling into this project before doing some serious research.
We made a worm-gear drive this year out of a piece of 1/8" thick boxed aluminum and a bronze spur and stainless worm from Applied Technologies. I would NOT suggest buying from McMaster Carr. McMaster only sells cast iron worms, which will turn to dust after a few matches.
If I were you I would spare myself the grief and buy a contained unit such as these:
-http://www.applied.com/apps/commerce/catalog/catalog.do?e=2&c=1960
-http://www.chiefdelphi.com/forums/showthread.php?p=566568#post566568
-http://bostongear.com/products/enclosed/wgsr.html
If you have the resources to machine a gearbox I’m sure you have the resources to cheese-hole one that’s already made 
(You can see the gearbox on the side of the T. REX’s arm)
True, cast iron does wear very fast, so the next best thing is to get bronze worm gears and steel worms, both which you can get at SDP-SI
https://sdp-si.com/eStore/
They have both smaller nylon worm gears (perhaps too small), but larger bronze worm gears which I think would suit your application. If you do order from them, please order as soon as you can because our team has had some trouble with delayed shipping (in our case, gear stock).
sorry to bring back a kinda dead topic. But would it be considered legal to buy a worm gear box from Boston Gear.
I dont believe it would be illleagal, I mean check the FIRST part flowchart in the Robot section of the manual. I believe the only probnlem you would have with the one you buy would be for weight and size constraints and also if your team is budgeted on there money.
Calvin,
The gearboxes shown are mostly for fractional horsepower motors but if you find one that you could use… They are restricted by the single part cost and must be accounted for in your BOM and max robot cost accounting.