Thread: Crank arm question

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Hi everybody!

I have a question. I ordered a wiper motor from Monster Guts and it came with this little crank arm thingy:



Does anybody know how you are supposed to attach the longer arm to this? I don't want to try and remove this big ball ended thing if I'm not supposed to, but I don't know how else you would get a longer crank arm to attach to it without taking it off of there first.

So, my questions are: Do I need to take it off to fit the longer arm on there or am I missing something? If I do have to take it off, how do I do that without ruining it? And once I take it off how do I get it back on again?

lol! I'm a total noob with this stuff so I hope there isn't a really obvious answer to this question that I'm just not seeing on my own!

Thanks for your help!!

-Mordessa

You can remove the ball and drill a couple of holes for bolts to hold longer hunk of metal to it.Or if the hole at the left of your pic is the mounting hole for motor then just make a whole new arm the length you need.

Hello, I have done both. The ball is a bit hard to remove I used a hack saw and then drilled the rest out. The little arm has teeth on one side to help with the crank not slipping when the motor is torquing. But an easy thing to do is just go buy some aluminum stock and cut the length you need then just drill the appropriate size hole and you are all set. You can also just use the ball for certain things. I drilled a same size hole in some pvc and gently forced the ball through and had a perfect set up for my leaning prop. Just cut the pvc 3/4 size to the length you need and you have a crank arm. For an Fcg type crank I would go with the aluminum stock or something similar.

I made my own using 3/16" thick aluminum. I drilled the hole for the motor shaft slightly smaller than the shaft. I used a socket that fit around the shaft and tapped the aluminum down onto the teeth on the shaft. The teeth cut nicely into the aluminum and the bolt gave me a solid joint. It is important to get the aluminum level or you may have issues with the aluminum bar hitting bolts on the wiper motor or with alignment for the rest of your mechanism. BTW, this setup is used to raise and lower a bucky arm.

are there any such things as crank arms with a square opening? and where do you get crank arms anyway?

Originally Posted by mementomori

are there any such things as crank arms with a square opening? and where do you get crank arms anyway?

I made a crank arm for a rotisserie motor that had a square shaft. Just drilled a hole and then used a small file and squared out the corners of the hole.

Ok, so I just need to hack off that ball part and drill out the hole that's there... so then when I put the bolt in that will be holding the larger crank arm, can I put a nut on both sides of that hole to keep it in place, as long as the long crank arm is not obstructed by it, or is there another way to do it?

I've seen pictures of props where people have done that. I don't have a lot of faith in that technique because depending on the load put on your motor, the nuts you put in can loosen and then your prop doesn't work. Here is a link to a nice peeker prop that Beacon Samaurai did. It works fine in the video, but MY fear would be that the extension joint would loosen. We have so many animated props we have used over the years and I've learned to do my best to bullet-proof them rather than spending most of my Halloween night fixing props that broke down.

Tombstone Peeker

I would suggest 2 holes with nuts and bolts.That way there is no way the arm can spin or twist.