Battery Buggy B

[fleet130]

the motor is melting. the wires burn as a result.

Heat damage to the motor is caused by excessive current. I can think of 3 things that might cause this.

1. 1. You're using more or less voltage than the motor is designed to operate on.
   
   2. The braking mechanism stops the vehicle without shutting off the electricity to the motor.
   
   3. The transmission's gear ratio is too low to produce the torque needed to drive the vehicle.

Solutions to the first two causes are fairly simple, although they may create other problems.

1. 1. Change the battery voltage to what the motor is designed for. (if the motor doesn't have enough power to drive the vehicle, see #3 below.)
   
   2. Add a switch that turns off the motor when the brake is applied.
   
   3. This is the more difficult problem to solve. It's caused by requiring the motor to produce more torque than it's designed for. If you're using just a pulley on the motor shaft connected to the drive wheel/axle with a belt(rubber band?), this may be the case.

When a motor is first turned on, its resistance to current flow is low. This allows relatively high current through the motor which produces higher torque (and) a lot of heat. As the motor speed increases, it generates an opposing voltage which reduces the current, torque and heat produced. If the motor is required to produce too much torque, it can't reach the speed needed to reduce the current to a safe level. The motor is unable to get rid of the excess heat and things inside begin to melt.

The solution is to reduce the necessary torque by reducing overall vehicle weight and/or by increasing the transmission gear ratio. This, of course, may require a lot of design changes to your vehicle.

[Jocool]

thanks, i hope this will help us.

[new horizon]

how do you tell when your gear ratio gets so high that the motor could potentially melt?

[fleet130]

how do you tell when your gear ratio gets so high that the motor could potentially melt?

To be technical, it's the other way around. The motor will overheat if the gear ratio is too low. A gear ratio that's too low can also make travel times inconsistent. If the gear ration is too high, the vehicle will just travel slower.

The motor will get too hot to touch comfortably. The vehicle should accelerate to its maximum speed within a few feet from the start. If it keeps accelerating throughout its run, the gear ratio is probably too low.

[Jocool]

The motor will get too hot to touch comfortably.

That's what happened our first time, only we used a rubberband and pulley, not gears.

[new horizon]

sorry, i'm a little confused.

so, gear ratio is calculated by gear attached to motor:gear attached to axle right?
So, I've come to learn that big power little means a faster speed and less torque, while a little power big means lots of torque but not a lot of speed.

So wouldn't a large gear ratio cause lots of speed but not enough torque to get the buggy moving, causing it to overheat? right? or am i mistaken?

[Jocool]

what if you have a small gear, a bigger gear, a big gear, then a small gear?

[fleet130]

So wouldn't a large gear ratio cause lots of speed but not enough torque to get the buggy moving, causing it to overheat? right? or am i mistaken?

The vehicle whose transmission has a larger gear ratio will travel slower and have more power.
http://en.wikipedia.org/wiki/Gear_ratio:

# The gear ratio is the relationship between the number of teeth on two gears that are meshed or two sprockets connected with a common roller chain, or the circumferences of two pulleys connected with a drive belt.
# The ratio of the speeds of rotation of the initial and final gears in a gear train

If a motor makes 20 turns for every turn of the transmission's output shaft, the gear ratio is 20:1, 20/1, or 20.
If the motor makes 40 turns for every turn of the transmission's output shaft, the gear ratio is 40:1, 40/1, or 40.
The second example has a higher gear ratio and will travel more slowly and have more power.

A higher gear ratio decreases speed and increases torque. A lower gear ratio increases speed and reduces torque. A vehicle with a 20:1 ratio would go faster than one with a 40:1 gear ratio IF the motor is capable of providing enough power. If not, the motor will overheat and possibly melt down and destroy itself!

To find the gear ratios between two gears by comparing #of teeth, diameter, radius, or circumference instead of speed of rotation, the numbers go in the opposite order. An input gear with 10 teeth meshed with an output gear with 40 teeth would have a gear ratio of 40:10, 40/10, or 4.

The key is that the speed of rotation of the input goes in the numerator and the speed of rotation of the output goes in the denominator.

Edit: Jocool, you need to post a diagram or photo.

[new horizon]

ah, i get it.
thanks.

and does anyone know the formula for calculating a complex gear ratio? i found a site with it but i forgot to bookmark it...
iirc it was
if the first gear ratio was 15/1 and the second was 5/1, you take the 15 and multiply it by the 5 but i'm not sure....

[fleet130]

The final ratio is equal to the product of the individual ratios, so the ratio of a 15:1 driving a 3:1 would be 45:1. Sometimes it's easier just to count how many revolutions the input makes for one revolution of the output.