# Wiper motors - How to turn a 5/16 threaded bolt with a 6mm threaded mount



## Devils Chariot (May 23, 2007)

Hi Guys,

I am trying to fix my Grinder Creep prop. It had a large turning crank attached to a wiper motor with the 6mm threaded mount that you'll find on the motor, a 6mm coupler, and a 6mm threaded shaft. The weight of the crank eventually snapped the 6mm shaft in half after about 4 days.

I rebuilt the crank assembly with a 5/16 7" bolt and it is strong and turns well. The problem is I don't know how to turn the 5/16 bolt/threaded rod with a 6mm threaded mount. I am not very hardware savvy, so while I can find coupler of the same size at the store, and a few that step up or down a size, I cannot find anything the can couple metric to imperial.

I tried a pulley system but the belt kept slipping.

I was wondering if there is some kind of universal coupler where you can buy each side in whatever thread you want, but they connect in the middle the same.

It's one week to halloween and I really need some suggestions! :zombie:


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## Otaku (Dec 3, 2004)

If you want to go back to the pulleys, you could try timing belt pulleys. No slippage.

http://www.mcmaster.com/#timing-belt-pulleys/=el8n0y


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## Devils Chariot (May 23, 2007)

Hey otaku,

My pulleys were just like those. i bought them to build a roto molder originally.

I am wondering if a bike chaint and sprocket set up might work.

With my pulleys it seems like the nylon belt was to prone to flexing and stretching.

I might have to just try a wider pulley and wider belt.

edit:

this give me an idea:









I think I can mount a disc of plastic or MDF to each end, then connect the two disc together.

I'll try that.


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## Otaku (Dec 3, 2004)

Wow, how much friction/load are you trying to move? Chain would be better, I think, as it doesn't stretch. Might be noisier, but that may add to the effect.


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## Devils Chariot (May 23, 2007)

It's this guy:






Most of the friction I think comes from moving/pulling his arms.

My pulleys only had a 1/2 wide belt. I think something like a 2" wide belt would drive it.


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## Otaku (Dec 3, 2004)

Yeah, I remember that guy! The motor seems to be almost stalling when its lifting his arms. What happens when the arms are disconnected? You sure a wiper motor is up to this task?


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## hedg12 (Jul 6, 2008)

Grainger has a pretty good selection of motor couplers, if you're still looking for an in-line coupler.
If you use a chain or belt, you could reduce the drive ratio (use a bigger pulley on the crank and a smaller one on the motor) to present an easier load on the motor. The crank wouldn't turn as fast, though.

That prop is awesome, btw!


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## Devils Chariot (May 23, 2007)

Hey Hedg,

I did have a good set up with my pulleys like you described, i just think the belt is too narrow.

Th grainger site looks promising. I am going to try one cheap thing tonight, and if doesn't work its off to Grainger.


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