Thread: Bi directional Wiper Motor

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How can I get a wiper motor to spin one direction for 5 seconds and then the next direction for 5 seconds? I have built a 12ft tall guillatine and need the blade to go up and down. I have the roap going from the blade to the top and a pulley up top and the roap back down. i just need a motor that will change directions so the blade goes up and down. Any suggestions?

Rope, not roap sorry

Someone on this forum shared a website. I can't remember or find it right now but I made a quick sketch of what I wanted to show you. If you make a rack and pinion style do-hickey you can make a motor that spins one way make a reciprocating motion.

Here's the sketch:

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You could use a relay and 2 limit switches, ! at the top and the other at the bottom . When the blade makes the switch it wil reverse the polarity and the motor will reverse direction.

Do you need to have the blade pulled up the entire height of the guillotine? If so, that's a long throw (I'm assuming 8-10 ft). How do you plan to wind the rope, a large pulley or drum spindle?

If you play with the dimensions, I think your best bet is a 4 bar linkage.

(crappy but effective video)



(rope at the end of the red piece)

Change up the dimmensions of the bars, especially the pivot point on the red piece to get the amount of motion you want.

Ive thought about doing a prop similar to this as well. My idea was to use 2 bicycle gears and a chain. I would attach 1 gear to a "spindle" and tho other to a corded drill. Then use a simple on off relay on the drill (with the trigger forced down with a simple hose clamp). I do not have anything on paper, and some type of slip gear system would be needed to keep the spindle from spinning backwards when the drill is not running.

After rereading this it sounds pretty confuseing but I will post again once I have either a working prototype or at least a better description of my idea.

Originally Posted by Crunch

Someone on this forum shared a website. I can't remember or find it right now but I made a quick sketch of what I wanted to show you. If you make a rack and pinion style do-hickey you can make a motor that spins one way make a reciprocating motion.

Crunch, here's the site you were referring to:

http://www.robives.com/mechanisms/recip

If you are going for any form of realistic with this prop you will need a free fall on the blade and use the motor to bring it back up. A 8 to 10 foot drop will be slow going with a wiper motor. Not slow slow but it won't look natural for a guillotine.

You would need to incorporate some type of a clutch into it that will let the rope free fall in one direction and the motor engage to bring it back up. Something like this...



If you have one of those drop down spiders that drops about two feet then raises back up you could take it apart to see how it works because that is what you need but on a larger scale.

Originally Posted by bfjou812

You could use a relay and 2 limit switches, ! at the top and the other at the bottom . When the blade makes the switch it wil reverse the polarity and the motor will reverse direction.

bfjou812: How do you use a relay to switch polarity? I can see the first switch to start the motor, and when it hit the second switch...then what happens?