So I've got to make a motor car...

[pcgamer4life]

For physics class we've got a project to make a gravity powered car, and then we've got to make a motor-powered car.

We've got to get a specific motor, it's a 1.5-3.v motor, max 8300 RPM, from radio shack. Of course, the winner won't be based on output of the motor alone, especially if all the motors are the same, it'll all come down to design and how you get the power to the wheels.


As of now, I'm not sure how I'm going to go about driving the car, I've basically got two choices, gear driven or belt driven. Gear driven will theoretically throw more power down, but it'll be a lot harder to keep the car in a straight line, as opposed to it doing donuts. The belt driven, probably a rubber band, can create more problems, the belt breaking/falling off. So I'm not sure how I'm going to do this, and I'd like input.

Also, is there any way to make the motor max out it's potential? It's rated at 8300 RPM, but I'm not sure if simply throwing 3v (two AAA's ) will make it run at that. I could try overvolting the motor, but not sure if that'd be smart to do, or if it would yeild any performance at all.

On a side note, the idea of a "nitrous" system popped into my head. For example, if the car's motor didn't have a max voltage rating, I could charge a capacitor and discharge it remotely to give the motor boost. Of course, that's probably not even productive, but it would be really cool. :p

[hrhrhrFOOT]

Get the drag coefficient as low as possible, if what you say about the engine limitations is true. Also, get weight down as low as possible. Try to make the car wider as opposed to narrower cause that'll help balance...I know this is common sense, but that's what gets it done ;p

[ATF 2GTalon]

You can play with gear ratios as well. If you want fast acceleration go with a smaller gear but it will be top speed limited. If you want top speed go with larger gears, but it will have slow acceleration. Depending on the length of the track, it'll take some trial and error to get the right gear combination.

[flaughert]

How many batteries are you allowed? Those motors can take more than 3 volts it just kills them faster.

[Borisw37]

What is the goal of this project?
Make a motor powered car?
Make it go straight?
Make it go far?
Make it go fast?
All of the above?
Once we know the required criteria then we can focus on the solution.

[zebkoolindc]

I'm sure your teacher won't let you use more that two 1.5V batteries. But that doesn't stop you from having a higher voltage.

You can find these small 'N' sized batteries that are 12V each. If the teacher would let you put two in parallel you would have much more power.


If the teacher says you have to use two AAA's there is no reason you have to have 3V. A LM2578A will step up your 3V to 6V or higher.

I don't know if you have the skill to build the cicuit to do it, but if you want to try the data sheets are Here (http://www.national.com/pf/LM/LM3578A.html#datasheet)

[knightwolf6543]

ahhh i remeber doing something like this but it had to stop at a certain distance for the science olympics, lol, yeah i would look into gear reductions, and for belts go into ur local hobby shop and ask them for some belt gears, they should have some belts that are better then a rubber band.

[orionlion82]

its gotta run for the instructor and not much more?
sure get a tiny transformer in there and overvolt it. (6V?)
outside the box overclocking allpies.
harder wheels are more efficient.
rechargable NIMH/Lion batteries (they come in standard sizes) i believe pack more milli-amp-hours than conventional batteries, so hitting them harder even with a transformer (heck, without it) yields more energy density.

its all about power/time and efficiency.
this is how you will impress the instructor.
build it light, strong, powerful and efficient, and youre well on your way.
the rest i would reccomend has allready been covered in this thread

[knightwolf6543]

balsa wood, light and strong, when i mean lite i mean LITE!

[Tc3 Toad]

Here are a few drivetrain setups that I threw together:

2wd- The bottom one is your most basic setup. The top is an interesting multi axle design.
http://i3.photobucket.com/albums/y72/Tc3Toad/3D/2wd.jpg

4wd- The left one would prolly provide less torque steer due to the motor spinning oppisite of the driveshaft. The right one could be made 2wd by removing the drive shaft and make it more efficient.
http://i3.photobucket.com/albums/y72/Tc3Toad/3D/4wd.jpg

[Moto7451]

I take it these are drag cars? You probably don't need to worry about driving more than one axle if thats the case (since you're using one motor).

I would buy two of the motors and run one at various voltages. Basically think if it as a race motor. A Stock car motor doesn't have to run for 100,000 miles, it only will have to run 600-700 per weekend at most. A top fuel dragster only has to run at full bore for a little under two minutes in total before its torn down and rebuilt. Just keep that mentality ;-).

If you only need to run it three or four times, who cares if it will die after 20 trips at 24v ;). Just try to make it so that you can easily put a replacement motor in it :D.

I would recommend using Sanyo batteries as well. They work well in situations like these. They have very good current transfer properties.

Edit: Another thing I forgot to mention is that there will be differences between the motors and if you are barred from over volting the motor, try to find the best motor you can. I've found differences up to 100RPM between "identical" motors.

[XDVD]

If you run the motor at too large of a voltage you will burn the brushes up faster. If you can find a similar motor (but that takes more power) you can switch the brushes out. I did that for a robot project for college and was able to run similar motors at considerable more power.


Really, I doubt you'd burn the brushes up that fast with almost any power you throw at them. One thing to consider, try to get as light of a battery load as possible w/ as much power (the batteries will probably be your biggest / easiest weight variable to change).

I'd really like to see what happens if you take one of those capacitors out of a disposable camera and charged that up to power your motor. I'm sure it'd discharge way to fast, but it'd be interesting.

Also (sorry if I missed it) what is the goal for the car? Do you want the fastest, or the furthest driving, etc.

If it's distance I love using CD's for the wheels with lego barrels ( http://images.google.com/images?q=tbn:UNLa07hlguOzhM:http://media.peeron.com/ldraw/images/6/30139.png ) pushed through / glued in the spindle hole. Lego axels work especially well if you throw some fishing reel oil on to the axle.

[Captain Slug]

You might want to think about the best ways to reduce weight while still making the end product as simple as possible. I think it would be best to simply use wide rubber bands or O-rings as a tread. You can pick the rear wheel/pulley based on the gear reduction you want to use for the best traction from the motor.

Keeps the parts to a severe minimum and make the end product as light as possible.

[Dukeman]

Thats a nice design but I would add some skids or outriggers (really light wire or something) just to enhance stability.

[Captain Slug]

That's what the front wheels are for.

[FireMogle]

Does the motor have to power wheels? I had a fairly fast car that was duel prop back in high school. Wide wheel base and low center of grav.

[Nephewkp]

You could also probably rewind the wire on the motor armatures to get better motor performance (thinner wire allows for more loops but at higher resistance) if you are allowed to do so. I remember winding more wire on my AFX cars to go faster....but be careful, after a long race several of my cars caught on fire after overheating (due to the above mentioned increase in resistance)!

Here is an article on rewinding procedure (this is specific to slot cars but the idea is the same for all dc motors)LINK (http://www.ncphobbies.com/rewind.html)

[demortey]

if you are looking for gears, small belts, pulleys and stuff i have a couple suggestions.

tear apart old colour printers for gears and possibly a couple small belts (and a really long belt), VCRs have belts and pulleys, old radios have pulleys to move the tuner. cassette decks are always good for gears.

CDs will make a perfect wheel, maybe glue 2 cds togather with some sort of round spacer that will give you like 1/8" or 1/4" to wrap one of those wide elastics around. just make sure if you do the single wheel in the back route (which would probably be the easiest design, looking at slugs drawing) that you get a nice wide space between the front wheels for stability.

gl on ur proj

[greyharte]

prolly late on this thread ... however you can also re wrap the coils on the motor w/ a thicker gage ... this is a common way of producing more power out of the rc cars electric motors