# Need help with Engineering design project

Need help with Engineering design project!!

For our low level engineering design class we have a semester long project. Im going to explain the project as clearly as possible.

It is a design competition in which we have to build a vehicle. This vehicle must utilize the potential energy of 5 gallons of water 6 ft off the ground. This water will travel through 1.25" pvc and make a 90 degree turn parallel to the ground. The water will come out here at the ground and somehow give our vehicle some type of energy. The goal of this competition is to harness this energy then pick our car up and move it to the start line. The car must travel 30 ft from the start line. Any distance it travels after 30 ft is considered 30 ft so we dont want to lose any efficiency here. The cheaper we make it and the heavier we make it the more points we get. My team intends to put a nozzle on the end of the pvc to concentrate the outpour of water to spin a small generator which will in turn charge a battery. This battery will have a switch that channels the power to a small dc motor that turns the axels on the vehicle.

My team and I went to a specialty electronics store today and they had no small generators, more importantly one of the guys there told us that there was no way that 5 gallons of water going through a concentrated nozzle would not provide enough power to charge the battery enough to power the motor to propel our car 30 ft. Is he correct?

I feel as though if we get the correct generator battery and motor combination then this will work. When I say combination i am talking about voltage/amps/watts etc.

If it will work then what combination should we go with? We want to make our car as heavy as possible but ensure that it travels 30 ft. What does everyone think?

If the energy stored in the compressed gas doesn't count as legitimate, you could always just--you know, attach paddles to a shaft, run the water over the paddles, and have the shaft connected to wheels or something. Much more 'direct' power transmission instead of trying to charge batteries and run motors. I mean, if you think about it; 5 gallons of suspended water IS a cell in a way; in that it is a store of energy. The idea it sounds like is to come up with a way to accurately use that water AS the source of power.

I mean, hey, you could just run tests. Drop the water over the paddle into another reservoir on the vehicle, and just keep adding weights until the thing hits 30 feet consistently. Running water through an (expensive?) generator to power a (small??) dc motor to move something heavy seems impractical to me, but hey; I've never done the project. :P

The starting line is not where the water base is. We have to use the energy in the falling water and then somehow store that energy. We then pick up and move our vehicle to the starting line. Direct transmission type deal wont work... Side note: If we were to build some type of vehicle that used the water directly, we can have no output of water onto the ground as it moves. The only place water can hit the ground is right underneath the base where our vehicle attaches to the base, before it is moved to the starting line.

also It doesnt really have to be heavy. It can be really light. We just get more points for more weight.

Personally, I would be very surprised if you could do this with that design. That system just doesn't sound efficient enough. You're losing energy cause not all the force from the water is hitting the paddles. You're losing energy cause no generator is anywhere near 100% efficient. You're losing energy in the motor. You're losing energy in the transfer from the motor to the wheels. And you're probably losing energy in a number of other ways.

Can you hold the wheels of the car as you move it? If so, you might consider using something like a rubber band to store the energy.

Does the weight factor in at the beginning of the challenge or the end? If you weigh it before, what about somehow catching all of the water (thus adding weight), then using it to turn paddles on the cart?

Yeah the rubber band thing is about the only other thing that we can come up with. Its going to be tough to get the energy from the drainging water to get the rubber band to wind. We can hold the wheels while we move it to the finish line. The finish weight is what is used to compile the score. I guess I am going to start thinking about a rubberband type design. We will most likely end up catching the water some how and use the weight of all of the water to wind the rubberband around the axel. The electronic way would be somewhat costly anyway. I just figured it would be extremely cool if we could find a way to do it.

well, the electronic storage method is not a bad way to go, but i do agree that you have a lot of losses when you go this route. especially if you go for a low cost solution.

however, given that it was your original idea, here's a few pointers
as for a generator, you could just run a dc motor in reverse... (spin the shaft with the propeller). you might want to look into using super capacitors for storage instead of a battery as charging them is MUCH faster. if you manage to do the back of the envelope calculations to figure out how much power you'll get out of the motor with a set of super caps charged by your water system, you could probably gear the car well enough to get you to the 30ft (i'm just guessing here, i have no efficiency calcs, it is really just a gut feeling).

the other method of spinning a rubber band around the axle is not a bad one, however, unless you have access to a machine shop making the ratcheting mechanism that will disengage the rubberband could be irritating!

another option would be to use a spring/ratchet mechanism to store the energy (in my view you'll always need to use a set of paddles to spin... something!).

best of luck.

Would it be allowed to use the five gallons of water to raise a counter weight of just less than five gallons 6 feet off the ground.
Then eject the five gallons and use the raised counter weight to turn the axle of the vehicle via a pulley system as it falls.

Danger
Gold Member

I'm not confident about the efficiency of this, but it should also be possible to store the energy as compressed air (perhaps in something as simple as a balloon) on-board and use it for either jet thrust or to power a small turbine similar to one in a pneumatic wrench. I'd feel far better about that if the water didn't have to exit the pipe at floor level, as was indicated in the original post.

Can I be cheeky and suggest you mount a 5 gallon tank, very very nearly 5 feet above the ground but on your vehicle.

Then simply let the water run from their tank into yours.
You will have as near as dammit captured all their energy.

Then let the header of water drive whatever mechanism you choose.
You can concentrate on a low friction, low loss drive.

This will have the advantage of transporting an extra 50 lbs to the finsih line.

Good luck.
Happy wheel spinning