# Engineering challenge (car)

Discussion in 'The Projects Forum' started by roadkill, Jan 23, 2011.

Jan 23, 2011
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I'm taking part in an engineering challenge and I have to build a car that can move forward and reverse in without using a remote control, it can have no energy to start off and it has to go back and forth as many times as possible. I'm not allowed to touch the car while it is in motion, only I am allowed to power the car and everything I use to power the car must be on the car while it is in motion. I'm thinking of powering the car using a rechargeable battery that will be charged using a hand crank. Does anyone have any suggestions on how to make the car switch directions without loosing too much power or time?

2. ### magnet18 Senior Member

Dec 22, 2010
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How far does it have to move?

3. ### beenthere Retired Moderator

Apr 20, 2004
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Arrange the bumpers so they are connected by a flat bit of metal or wood that runs in a channel on the frame, so it can only move back and forward. Arrange a hole in this flat connector so it fits over a slide switch. When the car runs into something, the bumper will displace and move the switch to reverse voltage to the motor.

4. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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Is the surface the car is on flat, or curved?

What is the size/weight of the car, as well as distance needed?

5. ### magnet18 Senior Member

Dec 22, 2010
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In addition to these, how much voltage do you expect to get from your battery?

6. ### tom66 Senior Member

May 9, 2009
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If you're super concerned about battery life you could also consider using regenerative braking to recharge the cell while stopping and going in reverse - could add some cost, though.

7. ### wayneh Expert

Sep 9, 2010
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Keep the mass low unless you're able to recover most of the braking energy with a flywheel or such. Reversing momentum takes energy. Period.

This means rechargeable battery is maybe not so good. Heavy and inefficient at storing energy delivered to it.

8. ### jpanhalt AAC Fanatic!

Jan 18, 2008
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Who said anything abut the car being on a surface? I was going to suggest just hanging it from a string and make it swing like a pendulum.

edit: Actually, the pendulum might be a bit extreme, but it does represent an area to look at. Why waste the energy going back and forth? I was think of something like one sees with elevator cars, cable cars, etc. where one is using gravity and inertia to minimize energy input.

John

Last edited: Jan 24, 2011

Jan 23, 2011
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Thanks guys i thaught of a pendulum and it's not allowed because it has to be a vehicle. We arent allowed changing the track and it has to travel about a meter. it has to fit in a regular box and no weight limit any ideas will help a lot.

Thanks

electrical_engr likes this.
10. ### jpanhalt AAC Fanatic!

Jan 18, 2008
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What is the nature of the "track?"

How big is a "regular box?"

I am thinking of something like a clockspring driving the wheels. That will conserve the energy from stopping probably better than a battery charger. A capacitor could be charged in the stopping and electronically reversed to help power up for the return.

John

Edit: By clockspring, I mean the oscillating regulator or escapement, not the main power spring in a wind-up clock.

Last edited: Jan 24, 2011
11. ### mcgyvr AAC Fanatic!

Oct 15, 2009
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How about a timer on the h-bridge. Motor runs forward for a set time, then the timer switches the h-bridge to make the motors go backwards for a set time..and over and over again.

electrical_engr likes this.