Elastic band powered vehicle

[jk]

Thanks for the look.

I have to make an elastic band powered car for Uni. to carry a weight of 2 kilos over a distance of 12 meters. The weight must be dropped at twevle meters, the car is not required to stop. The elastic band (which is the sole power for the cars movement), is 6mm in width and has a circumference of roughly 200mm, it must be 1.5 mm thick or so. (no. 65 elastic band if that means anything at all to you). The weights come in the form of 2x 1kg iron weights, so the elastic band must be able to be stretched without contact to these space takers.


I have just over five weeks to hand it in by and am just considering different methods at the moment.
I'm not asking for instructions, I would just appreciate some different ideas and different things to think about considering.
Im interested in RC vehilces and would like the weight to be dropped via a remote controlled hatch. I understand this isn't the easiest way to achieve my goal, and being a Mechanical Engneering student, prehaps I should look for a simple route to achieve the same goal that a complicated one would but none the less I want to make it more complicated, because i want to be able to make my own RC vehilces one day.
I was thinking of using a CVT system for the gears to start of slow and not waste any of the elastic bands energy ( I assume this).
Also another simple idea is of using some thin wire, and attaching it to the elastic band in order to cause the tensile forces to be spread through both the elastic band and the wire in order to spread and conserve the energy to help the vehilce reach the 12m dis. I will use some form of rubber on the wheels maybe elastic bands.

I will pounce upon any information you give so give anything you've got. Any tips or anything to do with gear ratios, CVT systems, radio signals for RC vehicles, ideas for weight distribution etc would be greatly appreciated.

And I say i want RC weight drop mechanism but please still give other ideas. Thinking also of just making it mechanical and causing a latch to drop the weight after the wheels have revolved say 30 times, I could attach string to the gears which are measured to pull the latch after twelve meters, stopping the weight and prob. stopping the car.( but it must work every time).

I tell no lie, this is one of the first physical steps I've taken in this project, but i have had projects before and just wished i had got some help from here first so think this is a good first step this time round.

Thanks for giving me some of your time, James.

 

[MikeG.]

What a great project!!!

I would forget RC for dropping the weights......keeping the weight down is going to be really important. My guess is that the distance is 12m because experience has shown your lecturers that 10m is fairly easy, but that few get to 12.

So, this is going to be about efficiency of propulsion and low rolling resistance, which implies a low weight. An immediqte thought is to invetigate skids Vs wheels............would skids made of ice be more efficient?

The dropping of the weights should be easy........a 12m cotton thread held at the start line could pull a pin out, but if that is against the rules then a reel winding thread with movement of the vehicle should do the trick.

The usual elastic band propulsion method is via a propellor...........and you will need to check whether that is less inefficient than the gearing required to turn wheels.

My strong advice would be to examine the rules intensly. The winner will be the person who finds a loophole.......for instance, does the vehicle have to be exclusively powered by the rubber band? You are carrying 2kg of weights......why not make them work? Raised high and allowed to fall slowly under gravity this weight would produce many many times the amount of power of that rubber band.

Anyway, have fun.......it sounds a great project! We will, of course, need photos.

Mike

 

[Maverick.uk]

The winner will be the person who finds a loophole.......

Hmm, when ever i explored loop holes and or did things explicitly not in the rules i always got penalised.......... I guess that will be down to the lecturer.

Cheers

Mav

 

[matt]

I think I'd be tempted to make the weight water in a balloon and somehow or other set a pin to pop the balloon at 12m.

(PS. My wife just glanced over my shoulder and said "the dung beetle is a regular contributor" . (based on the fact that she notices your icon whenever she happens to spot the forum on my PC)).

 

[MickCheese]

If you could somehow lose the weight once it had used it's energy then you would not have to continue to push the dead weight forward, ie water or sand.

Good luck

Mick

 

[NickWelford]

Given that the elastic band will have most power when fully tensioned or wound, you need to prevent spinning of wheels that waste energy. Perhaps think of some kind of flywheel that will store the energy and release it more efficiently. Or a spring, rather like a clockwork motor runs with.

 

[Chems]

Your main concern should be having the vehicle able to roll very freely with very little friction on the wheels, also the axels could probably be a ball bearing affair to help stop the weight affecting the rolling friction of the vehicle.

I think the trick here is although you have 12m on 1 elastic band you also have 2kg of energy to harness. Say for instance if you dropped them off in a way that propelled the car extra distance, that would be ideal. Some sort of cam system that you dropped the weight onto the pedal pushing the pedal down which then inturn drops the weight off the pedal onto the floor achieving your objective but also helping you travel those last few meters.

 

[head clansman]

Hi

the theory is easy peasy, putting the idea into action is down to you tension the elastic bands with the weight just enough to get you the distant or more would be better so when the elastic bands are unwound they drop the weights, simples. :lol: hc

 

[frugal]

I would be tempted to have some sort of U shaped chassis, with the open part of the U facing away from the direction of travel. Combined with some kind of weight powered mechanism. As the mechanism drops it power the vehicle. If you can calibrate the length of drop, the weights will hit the ground in the middle of the U-shape at 12m.

 

[Night Train]

Old cd's are often used as wheels in such designs as they have very little rolling resistance. They don't have much traction either but you might get some if you stick masking tape around the edge and then peal off as the residual glue might be enough to get moving with.

You may be able to store some of the excess energy at the start by lifting the weights as part of the process of eventually dropping them again.