Shaft Couplings

Well I've been fooling with this stuff for a while and if there are "standard" couplings I have yet to find them!

I figure you will need to hack something together yourself.

I can think of a few ways of doing this. It kind of depends on how secure you want the thing to be.

One way would be to fill the 1/2" hole with epoxy and then drill out the 5/16". But you would prolly need access to a lathe to get the hole concentric enough.

You could also try to find or fabricate a bushing that's 1/2" od and 5/16" id.

If you want it to be really secure, I would recommend that you make up another hub that is a good fit on the shaft, can be centered easily on the wheel and is secured to the existing plastic hub with screws.

If your search proves fruitless feel free to contact me off group. I can make up something that will work.

DOC

Buy my junk!

Hum...

I looked at the pic again.

6 inch wheels!

How heavy is this bot? 5/16 shaft doesn't seem like it would be beefy enough.

DOC

Unfortunately, I don't know of any "standard off the self couplers" like this. Everyone that I know of makes them themselves using a lathe. The best bet is to get a chunk of at least 1/2" diameter aluminum rod, and drill out the center for a 5/16" shaft. You can then drill and tap one end for 6-63 set screws to lock it on the

5/16" motor shaft.

The big question and or problem is how big and how heavy is your robot going to be? This sounds like it is a fairly large 20 pound+ robot. The typical gear motors aren't really designed to handle that weight directly, the inside end of the output shaft is barely supported at all. Thus you run the risk of gearbox failure fairly soon. The motors aren't designed to support the weight of the robot. If you don't have access to a lathe someplace. . . You should use a something like four 1/2" pillow block bearings for 1/2" steel rod, 1/2" steel tubing might work out nicely too. Two bearings on each side. Then run a small 5/16" bore #25 roller chain sprocket on each motor, and

1/2" bore #25 roller chain sprockets on the wheel shafts. Of course some other things would need to be done to, etc. For example, You can use "good" 1/2" long shoulder bolts for axles (watch out for the el-cheapo 7/16" bolts that have 1/2" threaded ends). Then measure three times and drill a 1/8 inch hole thru the shaft in the right place and put in a 1/8" piano wire pin and use a nylon based lock nut and some washers to hold the wheels onto the shaft. is a good place to check out all the neat goodies and parts to get too.

DOC, Earl,

the bot should be 20lb+. Here is a link to motor

am very upset reading your messages. I expected just to connect wheels to the motors and finish on that. Actually I already connected them using some hardware from Home Depot, but the distance between gear box and the wheel 2"+, that is too long for gear's shaft to stand 20lb. So I am looking for well fit and short adapter. ... I am crying ...

You're probably going to have to support the shaft on both sides of the wheel. But that's not too hard.

If you can find some 1/2" ball bearings, and some metal tubing with 1/2" OD and 5/16 ID, you're in good shape. If you can find 1/2" OD tubing with a smaller ID, you can drill it out larger. (Drilling a long centered hole in solid round stock requires at least a good drill press and preferably a lathe or mill.)

You can probably use aluminum tubing. Put in some steel 5/16 rod to fill the part that's not taken by the motor shaft.

Properly, you should put keyways and keys in everything to prevent slipping, but you may be able to get away with just using Locktite.

John Nagle

Ek wrote:

I am very upset reading your messages. I expected just to connect wheels to

Like John stated, you could support the axle on both sides. 1/2" pillow block bearings are easy to get. A good hardware store has them. The info for that type of motor states it is 15 pounds max overhung load. So supporting the shaft on the other side would work. That type of motor doesn't appear to have brass bushings or ball bearings on the output shaft, so one needs to be careful with the loads. Also don't stop the motors instantly or suddenly switch to reverse from forward on the robot. A 20+ pound robot wouls strip out the gearsright away. You have the robot slow down, the stop more gently, the speed up the same way. Of course if the gearmotor has beefy gears it may not be a problem. But then the wheels would have a tendency to come loose on the shafts.

> I am very upset reading your messages. I expected just to connect wheels

Thanks for ideas! I will be working on it.

P.S. Would be interesting to see what gear motors/whatever you would chose for 20 pound bot.

>> I am very upset reading your messages. I expected just to connect wheels