School fund raiser project

Community General Discussions
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I've been asked to do a small piece as a fund raiser for my Son's School - the idea is to make some small 'bots which will run around a course, either randomly then stop or round a fixed course for a random period of time (say 30 secs to 1 minute). I'd originally thought of bristle bots they're fun , quick to make and cheap - maybe 2 side by side linked "catamaran style". Ideally I'd work with the 10 yer olds to make them.

The idea is that they'll be used to select winners for a prize - pay fifty pence, if your bot stops on a prize winning square you get a prize!

Now's the question I'd throw out to all the electrical genii out there (and I know you are !) - what's the best way to set up either a random walk for a fixed period - or a walk for a random period.

If I go with a bristle bot it's got to be tiny and cheap - I'd wondered about replacing the battery with a capacitor, I could charge from a battery and it'd run till it ran out of Gas - would this work ? what size cap would give me 1.5 V for say 30 seconds ?? what are the rules for length of charging - I know nothing about caps. Anyone got any brilliant ideas for a compact under 10 gramme solution ?

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I was thinkging the same

I was thinkging the same thing as I read your post. However I think a capacitor is probably only going to run your bot for an unsatisfyingly short amount of time. A lot of BEAM robots use what is called a solar engine to charge up a cap and then discharge briefly into a motor. It works in short bursts. Probably not what you want.

It is possible with what is called a super capacitor that you might be able to do this. I’m expecting some parts in a few days and I can try it out.

 

 

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thanks Ignoble

I do have some 1.5 V rechargeables - I guess I could put these on charge for a few mins, see what residual charge I get over say ten mins  and then run them down. seems a bit crude though. I’d have to cycle the bots then as well.

I know what you mean about solar engines, but these seem to work in like 1/2 second bursts - too short really.

Anyone got a solution for a tiny circuit which could simply switch off after a random time ?