Faraday's Law. Here's another link to take a look at:

http://www.reliance.com/mtr/mtrthrmn.htm

Do we want to start a new thread, since we have now strayed far from the question in the original post?

Somewhat semantics, as the phrase Faraday’s Law of Induction is frequently used.

The key point to this thread, as shown in several graphs from your link, similar to the dyno graph I posted, is torque and thus current varies with RPM (switching frequency). Which is not explained by a simple resistance model.

It is a basic electrical circuit principle that a wire wound in a coil, especially around a core, has electrical inductance that is frequency dependent. A magnetic field makes it more complicated, but does not eliminate the inductance in the driving circuit.

Interestingly one of your other links leads to this simple stator model which includes inductance:

Dave, dont forget about leakage between the phases and Eddy currents

Use solder to remove the varnish on the magnet wire. You will need a really hot iron to do this. Otherwise, use a razor on each strand.

A rather simple observation got fairly weird didn't it.

Lol, I help design high voltage power supplies, you can over complicate this stuff until you go insane

Complex frequency responses of non-linear dynamic systems. I think it’s a requirement!

Cheers

LOL!


To the OP, you wont notice any significant gains. Put your effort into practice.

I can't say I ever expected anything much of it. If its not actually in the windings, as opposed to simply being an extension of them, it doesn't mean any more than the actual leads from the ESC to the motor, especially with the large gauge wires some use to connect things. You couldn't convince some racers, however. I've seen a few actually cut the wires away completely and solder the ESC right at the can. That's a little nuts, especially in a Tamiya mini class.

As for my driving, it's hopeless. Thanks for your remarkable input, guys. Without you smart folks, we'd be nowhere.

The behavior can be explained with a very simple model that includes a resistor but no inductor. But I would never model a motor as just a resistor.

I think the simplest model that gives useful results for a DC, permanent-magnet motor is a resistor (representing the total resistance in the circuit) in series with a voltage source (representing the back-EMF). We postulate that torque is proportional to current through the back-EMF source, and speed is proportional to the back-EMF. Then power output is equal to current multiplied by the back-EMF (torque times speed).

This model has reasonably good agreement with reality. It shows current decreasing linearly with increasing speed, and shows the output power peaking at 1/2 of the free-running RPM. The model requires no inductance to achieve this.

Inclusion of a shunt current source can be included for losses, and, when an appropriate value is selected, gives a reasonable approximation of the actual efficiency curve.

One can create a simple spreadsheet using this model, and compare the resulting curves with actual results. This might be interesting (and can give some useful insights) to our average reader, and it only requires a basic knowledge of electricity. I can send an Excel spreadsheet to anyone that desires it.

Yes, the mechanism that creates back-EMF is indeed related to that which creates inductance. The difference, of course, is that back-EMF requires an applied magnetic field, while inductance does not.

Including inductance in the model becomes important when considering commutation. In this case, the L/R time constant is important if it becomes a significant portion of the commutation period. (This is one reason why timing needs to be advanced at high operating speeds.) The motor model I mentioned above doesn't show this. But it does show decreasing current with increasing speed.

Let's do a simple thought experiment: We take one of our motors and remove the windings, counting the the number of turns as we go. Then we replace them with half as many turns, using thinner wire so we end up with the same resistance. To compensate for having half as many turns, we double the magnet strength (since back-EMF is proportional to the number of turns and the magnetic field strength). The motor will then have the same no-load speed, the same torque, the same power output, and the same value for the current at any given speed. But the inductance has decreased by a factor of four (since it is proportional to the number of turns squared).

Here's another (simpler) variation on the experiment: Let's replace the windings with the same number of turns, but use thinner wire so that the resistance is doubled. We make no change to the magnets. The motor will then have the same no-load speed, but half the torque, half the output power, and half of the current at any given speed. But the inductance has remained the same.

Most of us wouldn't notice any difference, including me. But I do know drivers that can make use of even a 1% power advantage, especially in a situation where it would be of greatest advantage, i.e in a class where the car doesn't spend much time at its grip limit (BRL 17.5 1s truck comes to mind).

In most other classes, handling is far more important than power. For instance, a 17.5 TC has more than double the power-to-weight ratio of a VTA, yet TC lap times might be only 15% faster. (This example uses lap times from our local track.) My experience with the Tamiya Mini is limited, but it seems that eliminating wheelspin is the number one goal, and once the wheels are spinning, then any more power is simply wasted.

That said, shortening the leads, or replacing them with a heavier gauge, seems pretty simple and easy (as long as one can solder well). Doing it MIGHT not give an increase in performance, but NOT doing it will DEFINITELY not give an increase in performance.

Do we want to start a new thread, since we have now strayed VERY far from the question in the original post?