Shaft Coupler


Long time no see hunn?

I'm almost finished mounting a magmotor dc motor/planetary gearbox onto my ATV steering shaft. I have a timing pulley on the shaft and another pulley on the output shaft of the motor. In order to protect the expensive gearbox I coupled the gearbox output shaft and the pulley shaft with a spider coupler.

Everything was good, until I had to actually mount the thing to the ATV and the only way I had was to mount it upside down. Needles to say, the pulley gets disconnected from the spider because of gravity.

Can you think of any other type of coupler that 1) will absorb some impact

2) it's not too expensive 3) does not get disconnected if forces are applied outwards

The other thing that crossed my mind is: with a timing belt, do I really need a spider coupler (instead of a rigid coupler)? Doen't the belt work as a shock absorber? Will it skip a teeth if a sudden and strong torque is applied to it? (i.e. the wheels hit the curbside at an angle).

I don't know if you'll be able to get the picture from my summarized words, if not, ask for clarification.



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There are all types of flexible couplers, though the spider couplers do tend to be among the cheapest. Browse the McMaster-Carr catalog with 'flexible coupler,' and scan through the pages. I see on the second page they have helical beam couplings, which may work for you. Note the torque ratings. Shear couplings are common on gas motor applications, and the coupling will fail before there's a chance to damage the power components.

You might also keep what you have if you can add a shaft collar. They come in various sizes and are available in both setscrew and clamp styles.

You may not want the rigid coupler even with a belt if the motor is gas (lots of sudden torque). I'd keep with the current design if possible.

-- Gordon

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Gordon McComb

I am not really clear why the pulley separates from the coupler when it's inverted, or why the pulley/coupler had to be inverted. If there is space on the shaft, could you put a collar on the shaft to prevent the pulley from falling down the steering shaft? Collars are very easy to make if you can't find one commercially. If you are not in a terrible hurry, and you can't find one already made, I'll trade you a collar with your specified dimensions (up to say 4" OD, 1/2" thick) for two six packs of stout or porter beer from a local (to you) microbrewery. I am near Phoenix, AZ.

It depends on the size of the belt. The narrow ones with fine pitch will skip pretty readily. An inch wide belt with 1/4" teeth will transmit a serious shock to your gearbox. How much you tension the belt will also be a factor in this.

A photo would help.

Regards, Bob

Note the Munged email address.

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"Gordon McComb" wrote

I did as you suggested and kept the spider coupler. This way I didn't have to change my design (and parts already fabricated). The shaft collar worked as a charm. The only addition to the shaft was to include a bearing between the shaft collar and my part to avoid friction. It's a cheap thing, basically a pair of washers with a nylon thing in between. The nylon thing has several holes, each one with a ball bearing within. This way the shaft collar will contact one of the washers and rotate almost freely without frictioning onto my part.

I'll post some pictures later on.



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