Author Topic: Building an Electric Car - How to optimize?  (Read 1350 times)

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Offline SchlayerTopic starter

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Building an Electric Car - How to optimize?
« on: February 24, 2015, 09:26:27 AM »
I have a little project to do for a segment of a competition between high schools. For this event, we need to make an electric car using a specific motor and it may only be powered by 1 or 2 standard 9-volt batteries. The car is scored based on how quickly it can drag a sled (a cut open cardboard box) carrying various provided masses (up to a total of 5kg) a distance of 5 meters. The scoring uses the following equation:

distance * (masses + mass on sled) / travel time

Basically, I need a way to find out the optimal gear ratio to use with this motor :
Any help would be appreciated!

Offline mklrobo

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Re: Building an Electric Car - How to optimize?
« Reply #1 on: February 24, 2015, 11:31:15 AM »
 8) Cool! I am on your side!  8)
The motor, in this case, will be your advantage. Balancing the
batteries, as a load, could be used to your advantage. A
lighter 9 volt battery, or equivalent? Find the lightest material you can to make
your electric car, as that can be translated to pulling power.
For your gear ratio;
What is the projected wieght of the car?
What is the diameter of the wheels?

Keep me posted....   ;D ;D

Offline SchlayerTopic starter

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Re: Building an Electric Car - How to optimize?
« Reply #2 on: February 26, 2015, 11:16:58 AM »
    The problem my friends and I have is that we can't know the coefficient of friction between the cardboard box and the floor. We are allowed to compete with up to five vehicles, so I think at least one vehicle is going to be super lightweight and designed to floor it (pun intended) with the cardboard sled carrying a fairly light load and just try and run as fast as possible. I'm trying to make my own vehicle one that moves relatively slow but pulls a lot of weight. Right now I'm intending to use some scooter wheels I found lying around - I think I recall they are 73mm in diameter. I decided to make my own car a bit less weight conservative, as we will need traction to pull a heavy load I expect it may actually need to be weighted down itself to pull a heavier load (>/= 2kg???)
    As we are limited to 'standard' 9V batteries (the rectangular block type) I think we're pretty much stuck with the weight of typical alkaline batteries. For our lightest vehicle, the builder used carbon fiber arrow shafts (hollow but strong and rigid) and made a 4 sided frame, and plastic attachments to mount the axel shaft in. That one will be the fastest by far I hope.
   The car I built has a wooden square frame with two sides mounted with down-facing aluminum L beams, to reduce friction with the axels. Everything is secured with steel bolts and hex nuts, and my axels are 5/16" thick stainless steel. I built it to be really sturdy in case we need to put a lot of weight on the frame for traction, but it's still not more than around 4-5 pounds by itself. Again, the motor we need to use is the same for every team, so there wasn't a way around that. I'll see if I can't show you some pictures of the frame of my car as-is.

Thanks for the assistance, mklrobo! :)

« Last Edit: February 26, 2015, 11:22:47 AM by Schlayer »


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