Someone has to know the answer...

[Rookie]

www.TeachEngineering.org: Free Curriculum for K-12

My daughter is building one of these for a school project. I'm trying to figure out gearing. I put the smallest gear on the axle, and I had to put the smallest gear on the motor due to the fact that the motor doesn't have enough torque to turn a larger gear. So, I put a third gear in the middle between the two small gears. It goes, but not as fast as I would like it to.

If I added more gearing, would it help? Any other ideas?

[indyjoe]

The electric motor will generate a certain amount of torque at a certain speed. You can gear up the car, but if you pass the level of torque available from the given motor, it will stall and the car won't move.

You can calculate the speed by taking RPM of motor x gear ratio (Driving Gear/Driven Gear) X other gear ratios as needed. Then multiply by circumference of the wheel for speed.

[Rookie]

I can set up any gear ratio I want. The motor will spin like crazy until you apply torque. Without any weight, I can put 10 to 1 on the motor, but it won't move on the ground. So, I ended up going 1 to 10 to 1 and it moves. If I added another gear inline, would it help?

[VN Vet]

HowStuffWorks "How Gear Ratios Work"

Wow, you are taxing my memory and my brain. I have not had this kind of question since my Engineering Physics Classes.

SO I won't mis-lead you, check out the above link. For others, do a google for gearing ratio.

Hope this puts you in the right direction.

[Rookie]

That's what I have...

[243rem700]

Are you looking for acceleration or top speed? With only two gears you will have to decide what you are going for. The smaller gear should be on the motor and the larger gear should be the driven gear for more acceleration. When starting from a stand still you will want the motor to spin faster than the wheels, increasing speed faster. For top speed you will want a smaller gear ratio. The amount of torque that will allow the vehicle to just barely accelerate without stalling will yield the top speed (assuming you have plenty of room to allow acceleration).

[Rookie]

The track isn't that long, so acceleration is most important. I've got three gears - left side of the pic is the third gear. The big gear is the biggest that is available. Are you saying that I should have the big gear on the axle?

[243rem700]

If the motor is powerful enough to turn it. For acceleration the larger gear should be attached to the axle. The middle gear is only essentially turning the driven axle.

[wolfman]

Reason for 3 gears is to allow the axle to rotate in the same direction as the motor. Small gear on motor, large on axle, check direction of travel, if you need to reverse, put second gear between the one on the motor and the large gear. Small to Small gear will give you a 1 to 1 reversed rotation

[243rem700]

Originally Posted by wolfman

Reason for 3 gears is to allow the axle to rotate in the same direction as the motor. Small gear on motor, large on axle, check direction of travel, if you need to reverse, put second gear between the one on the motor and the large gear. Small to Small gear will give you a 1 to 1 reversed rotation

You are correct. But the middle gear will not affect the ratio.