View Full Version : Small, model sized worm gear reducer

brian Rupnow
02-28-2011, 04:47 PM
I have another project underway (which has to do with the hit and miss engine I recently finished) and I needed a small, powerfull gear reducer that wouldn't back feed torque thru the input shaft. A worm gear reducer was my first choice, because a worm gear drive with a ratio of greater than 40:1 won't back feed. I happened to be "browsing" in Princess Auto, and found brand new wiper motor assemblies for $9 and change. I bought one for my new toy.

brian Rupnow
02-28-2011, 04:48 PM
I took it home and disassembled it, and found some very interesting things. First, the permanent magnets are glued into the motor casing, but readily release when the sides of the motor housing are heated with an acetylene torch. The housing itself is made from mild steel.

brian Rupnow
02-28-2011, 04:49 PM
The armature shaft is one straight peice, and the armature itself appears to be made from a stack of metal discs that are attached to the shaft with some kind of epoxy. It cuts easily with a carbide tool in the lathe. The copper commutator is not really attached to the shaft at all. It is held in place by the 2 miles of copper wire that are woven thru the armature discs and soldered to the copper commutator bars. Once the wires are cut away on the lathe, you can pull the copper commutator off the shaft easily.

brian Rupnow
02-28-2011, 04:50 PM
Since the motor housing is cylindrical with a flat on each side, the current plan is to make up a peice of aluminum plate that will fit into the peice of motor housing which has the flange on it and center drill it for a .3125 bushing. The shaft is 9mm, but since all my reamers are imperial sizes, I'll turn the end of the shaft down to .321' (5/16") 7.94MM and have enough shaft sticking out of the end of the housing/aluminum plate to mount a pulley on.

brian Rupnow
02-28-2011, 04:50 PM
And voila'---A really nifty little worm gear reducer. I will probably have to put some kind of collar on the shaft inside the aluminum endplate I will create, because depending on which way I rotate this thing the worm shaft will have a tendecy to "unscrew" itself from the worm gear. This wasn't an issue in its original shape, as there was a peice of nylon acting as a thrust bearing in the end of the motor housing.

brian Rupnow
02-28-2011, 04:51 PM
So there we have it---a beautifull little gear reducer. And this one is a 60:1 ratio.

brian Rupnow
02-28-2011, 04:51 PM
Add a pulley, and we're good to go. Man, that was almost too easy!!! as you probably noticed, i didn't turn the shaft to a smaller diameter. I used the full 9M and bored a peice of brass to 9MM to make the bushing----No reamers involved!!! ;D ;D

02-28-2011, 05:11 PM
Good idea at a great price !

Randy C

02-28-2011, 06:43 PM
I bought a similar motor at a similar price from PA in Cowtown for my pantograph tracer project.

IIRC, it was a RFE wiper motor.

02-28-2011, 07:01 PM
Ok, unless i missed something here, i,m wondering what this next project is?:D

Weston Bye
02-28-2011, 09:08 PM
...and found brand new wiper motor assemblies ...

That is what is known as a window regulator motor, for raising and lowering power windows. Years ago, I built a couple dozen durability test controllers for these things for a Fisher-Guide test lab. A similar but smaller motor was used in seat positioners.

The output gear engaged a stamped steel gear sector that had a lever that attached to the bottom of the window glass. When I wanted to repurpose the regulator, I found that a 3/4" (I think) socket wrench fit nicely onto the gear as an adaptor. From there I was able to fashion a square driving shaft.

02-28-2011, 09:14 PM
That is what is known as a window regulator motor, for raising and lowering power windows.

yeah ..i thought it was that .

all the best.markj

02-28-2011, 09:40 PM
Nice hack. By the way, those motors are fairly powerful for their size, so someone could also hack one just for the motor. As a windshield wiper motor it could be used on a more or less continuous duty basis- not sure if the window motor would be the same, but I think so. This would NOT be the case for a window motor with a wound field, only for those that are permanent magnet.

Back to the gear box- where I worked a while ago we had a run of mixmasters come in, the cheap handheld ones that KitchenAid makes. Those have a worm gear shaft and two worm wheels in them, also a permanent magnet motor. I kept a few dead ones for myself, intending to possibly cobble up a power feed for a light duty machine. The mechanism is quite compact and the motors are good- it's usually the multi-speed digital display electronics part that goes bad. If you can find one it would be another source for a worm gear drive unit.

brian Rupnow
02-28-2011, 09:44 PM
I stand corrected. I THOUGHT it was a wiper motor. I kind of wondered why it has "Right Hand" stamped on the case.:eek: :eek: What am I going to do with it---well, I want to build something to demonstrate how a hit and miss engine behaves under a load as opposed to under a "no load" situation. The gear drive is going to rotate an eccentric weight which will alternately load and unload the hit and miss engine.

02-28-2011, 10:21 PM
What could be cooler than a hit & miss window regulator?


J. Randall
02-28-2011, 11:37 PM
Good post Brian, I have one that looks identical saved from a Buick Regal , been going to see if I can turn it into a small winch for cocking a 150 lb. crossbow.

03-01-2011, 12:58 AM
Hmm- beware- I took one out of a buick riviera, looked similar- those things get hot quickly. If you're not using the motor though, this isn't something to worry about.

03-01-2011, 01:31 AM
We used a motor like that on a robot projec (FIRST), and found out a #25 sprocket meshes well with the motor output. It worked really well - 72 tooth sprocket and that motor makes a lot of torque.

brian Rupnow
03-01-2011, 04:45 PM
The crankshaft on my engine was just a tad too short to put a pulley on. It stuck out about .28" from the edge of the flywheel, which was enough to get a .093 dowel pin through for my electric start adapter, but no room left for a drive pulley. Today I took a peice of 7/8" dia. 1018 mystery metal and machined a "crankshaft extender". Its bored 3/8" to slide over the end of the crankshaft, and is dowelled in place with a .093 roll pin. The large diameter has a groove cut for on o-ring drive belt, and the other end is turned to 3/8" dia. and cross drilled for the starter roll pin.

brian Rupnow
03-02-2011, 10:51 AM
It gets curiouser and curiouser---The machined and split hub has a clamp bolt which locks the hub onto the driven gear. The 5/16" diameter bent rod is pinned into position in the hub. There will be a 1.5" diameter brass ball with a 5/16" hole through it to slide over the rod, and a set screw to lock it in place at various distances out from the center of the hub. once I get the mounting bracket made up, the gear reducer will mount so that the pulley groove in it lines up with the pulley groove in the crankshaft extender that I put on the hit and miss engine. Then when I put an o-ring drive belt on it, and if I'm very very lucky, the brass ball will slowly rotate on the end of the arm. The axis of rotation will be horizontal. that means that whenthe 5/16" rod "arm" is swinging from bottom to top, the engine should be "under load" and should fire every cycle. Once the brass ball passes over the 'top" and starts back down, gravity will assist it, taking the load off the engine and hopefully letting it go into "miss" mode. I chose to use a worm gear so that the weight of the ball would not "back drive" the engine as it is on the downswing.

Forrest Addy
03-02-2011, 12:27 PM
Brian's next project?

Well, he has this sow's ear and SWMBO needs a silk purse...

brian Rupnow
03-03-2011, 08:46 PM
Here are a couple of (from my point of view) interesting videos of the hit and miss engine under a variable load. It definitly does go in and out of hit and miss mode. However, its not CONSISTENTLY going in and out. Part of the reason for that is that my o-ring drive belt slips a bit, right at the crucial moment when the engine is supposed to be working its hardest to lift the weight. ---in fact, in one of the videos you can see my hand helping the weight "over the hump". Also, the fact that there is considerable tension in the drive belt (o-ring), means that there is some load on the engine all the time which imposes some load even when the weight is in the downswing side of its arc. The engine certainly doesn't lack for power. There are a couple of fixes for this belt slipping issue. I could go to a larger diameter pulley on the engine, which would give a larger contact area with the belt, but the slippage appears to be happening at the pulley on the gear reducer, not the engine. (All pulley systems slip a bit, its just not visible at high speeds). The better solution would be to substitute a pair of light sprockets and a roller chain for the o-ring drive and pulleys. A chain drive has a double advantage---zero slippage, and practically zero tension related drag on the engine. In the middle of one of the videos you can hear the chime that my wife rings to call me up to dinner!!! I have a two way speaker system between my office/test bench and the main floor of the house. The ratio between the engine crankshaft and the output of my worm gear reducer is about 137:1----not because I needed that much torque multiplication, but because I wanted things to happen in a slow enough time sequence that you could see and hear what was happening. As I started my preliminary testing, the first few weights I used were to puny for the engine to even notice that it was under a load. By the time I got to a load heavy enough to make the engine set up and take notice, the o-ring drive belt began to slip. I'm enjoying this, and it is very interesting.---Brian
http://i307.photobucket.com/albums/nn294/BrianRupnow/th_HITANDMISSUNDERVARIABLELOAD-2.jpg (http://s307.photobucket.com/albums/nn294/BrianRupnow/?action=view&current=HITANDMISSUNDERVARIABLELOAD-2.mp4)
http://i307.photobucket.com/albums/nn294/BrianRupnow/th_MovieHITANDMISSUNDERVARIABLELOAD-1.jpg (http://s307.photobucket.com/albums/nn294/BrianRupnow/?action=view&current=MovieHITANDMISSUNDERVARIABLELOAD-1.mp4)