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Electrical switch with a timer???

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For one of my engineering classes I am building a small vehicle that travels twenty five feet then stops in a five foot stopping zone then shoots a projectile to hit a five foot circular target ten feet away. It is coming pretty well and I am using a small electric motor I bought at Radio Shack to power it. But I need some sort of a switch that is on a timer so that I can turn it on and it will power my motor for twenty seconds then cut the power? Does anyone know of anything that can do this and where I can get one? Preferably cheap cause all cost for this is out of my poor college student pocket. Radio Shack has nothing....Thanks for your help.

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Research the 555 timer chip, with a change of capacitor size you can alter timing. Get a breadboard and play around a little.

I have used the 555 before for time delay on projects. Cheap and easy to use.

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If you have an aversion to electronics, or just want something old school, you can use gear reduction to control the rotation of a shaft that mounts a contact breaking cam or lever.

This would also be a control on the actual amount of motion without being affected by variations in speed.

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What are the rules? Grayracer's idea is a good one.

On the other hand if you want to impress us a plc, stepper motor, and optical sensor. (this is a little costly unless you can find some old equipment a factory is throwing away. Look at direct mail house's for some old equipment, they might just give it to you.

A solid state timer chip is also very convenient.

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Thanks for the input I'll try and see wh at I can come up with. Basically the rules are it has twenty seconds to accomplish the tasks and must be self o materialperated not remote control. No compressed gas or hazardous material and vehicle must fit in a 2x2 box.

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they didnt provide you with a PLC? if not, id take grayracers advice, or build a 555 timer if youre comfortable with electronics.

when i did my robotics lab in engineering, we were provided with a PLC, the rest was left to us, programming and all.

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Unfortunately we weren't provided with anything. I am not that familiar with electronics but now seems like great time to learn. If I can't figure it out I will have to go with what grayracer said. Maybe I will do both and see which one I like more. thanks again. I love TT.

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Now your a think'n man. Set your goals, and think of how many different ways to accomplish the same goal, then chose the best or most fitting. Major questions... how many ways can you solve problem X and more importantly, how many ways can you prevent problem X.

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Why use a motor at all? Why not a good old-fashioned wind-up device?

I like the way your thinking, but his question was about a electrical timer. I don't think he would score many brownie points for a wind-up toy.

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