High kv low gearing VS Low kv high gearing

[SpEEdyBL]

One thing that you guys are forgetting is internal resistance. Take two motors of the same design, one's 2,000 kv and the other is 4,000 kv, the 2,000 kv motor is going to have four times the resistance. So if you over tax the 2,000 kv motor by gearing for the same speed as the 4,000 kv motor, you will create four times as much heat in the windings. Of course the 2,000kv motor will draw a lot less current under acceleration, but it will also take a lot longer to get up to speed, due to the lack of torque.

A better comparsion of low kv vs. high kv would be comparing two different sized motors with the same resistance. For example, a neu 1521 vs. a neu 1512 and gearing for the same speed.

[sikeston34m]

Originally Posted by SpEEdyBL

One thing that you guys are forgetting is internal resistance. Take two motors of the same design, one's 2,000 kv and the other is 4,000 kv, the 2,000 kv motor is going to have four times the resistance. So if you over tax the 2,000 kv motor by gearing for the same speed as the 4,000 kv motor, you will create four times as much heat in the windings. Of course the 2,000kv motor will draw a lot less current under acceleration, but it will also take a lot longer to get up to speed, due to the lack of torque.

A better comparsion of low kv vs. high kv would be comparing two different sized motors with the same resistance. For example, a neu 1521 vs. a neu 1512 and gearing for the same speed.

I gotta disaggree with you on part of this Speedy.

The lower kv motor will make more torque than the higher kv motor.

The magnetism created by using more turns is greater, thus the torque is also greater.

[SpEEdyBL]

Originally Posted by sikeston34m

I gotta disaggree with you on part of this Speedy.

The lower kv motor will make more torque than the higher kv motor.

The magnetism created by using more turns is greater, thus the torque is also greater.

Not entirely true. Lower kv motors make more torque per amp than high kv motors, but high kv motors will draw way more amps. Also, when you use a smaller pinion gear, you also increase torque at the wheels.

I have tried both the Novak HV4.5 and the HV7.5 - two different kv's, but otherwise identical motors (listed at5,000 kv and 3,000 kv). The amount of torque the HV4.5 has over the HV7.5 is quite a lot. The 7.5 with a 14t pinion takes forever to spool up and is still slower than the hv 4.5 with a 9t, which is a rocket. Not to mention that a 14 tooth on the HV7.5 heats it up way to much. I guess if i was just shooting for 30 mph, the the lower kv motor would be better, because of the power required just to spin the motor, if that answers the question.

[sikeston34m]

Originally Posted by SpEEdyBL

Not entirely true. Lower kv motors make more torque per amp than high kv motors, but high kv motors will draw way more amps. Also, when you use a smaller pinion gear, you also increase torque at the wheels.

Let me explain this another way.

A high kv motor compensates for it's lesser torque with lower gearing. Lower gearing multiplies Torque, does it not?

A high kv motor does draw more amps than a low kv motor under NO load.

How many amps a motor pulls depends on how loaded it is. This applies for ANY motor with ANY kv. The higher the gearing, the higher the load is for the motor.

A lower kv motor has MORE torque. Torque is it's ability to overcome resistence. There is a way to measure it. This statement is true.

The lower kv motor is geared higher because it doesn't need such a low ratio to multiply torque.

Now back to the original purpose of this thread.

High kv low gearing VS Low kv high gearing.

Total Watts of power delivered is what needs to be considered.

A Lower Kv motor geared higher will pull more amps. If it were possible to match two setups, one high kv low geared, and one lower kv high geared where they drew exactly the same amount of amps on the same voltage.

They would deliver the same Total Watts of Power. They would be the same!

Watts = Amps X Volts. Higher voltage setups trade amps for volts in this equation. Wire size is limited in RC. We don't use cables the size of our thumb. The largest wire size most use is 12 Ga. 12 Ga. wire has it's limits. The greater the length of the wire OR the smaller the gauge wire, the greater the resistence AND the greater the voltage drop. This hurts efficiency.

The Total amperage drawn is what creates heat especially in wiring that is being pushed to it's limits. Heat is wasted energy.

The final voltage delivered to a motor, after voltage drop values due to wire size is considered, is enough to affect overall performance.

Any differences in the setups would stem from differences in overall efficiency. Lower kv motors tend to be more efficient because higher voltages are used with them.

Also Lower kv motors are more efficient for 2 reasons:

1. It doesn't have to spin up to such a great rpm.

2. The phase switching on the ESC is less.