# My motor controller dev thread

It’s AC of course. It’s on the motor side (AC side)

BEMF affects the ratio between DC / AC side. It’s bit hard to describe clearly… I can try to give an example if you’re interested.

I need to say that the BEMF does not necessarily stay close to the AC voltage.

Okay, so we are calculating electrical power here, right? But, should we also mention the current = torque, so in all these three examples, shouldn’t we still get roughly the same torque?

You got skype or voice comms where we could ramble?

Where are you located @SimosMCmuffin

I’m happy to have a Skype ramble with you about that stuff.

Did I understand that right that you want to make your own ESC?

I have already designed and run one, but I’m working on the next iteration.

I’m interested now in the analogue of horsepower and torque in cars.

Because we know that current = torque, but how does the power factor in…

Okay, now I start to see my theory go wrong

After a good night’s sleep and allowing my head to process stuff during the night. I have a new model to explain things, but it’s not good enough yet that I would know how to draw any graphs of it.

But I’ll try to set up the basis here.

So as we have now concluded: Power = Torque x RPMPower = Current x BEMF

So to have a steady acceleration we need constant power and not torque.

In the beginning when our motor is not turning we need more torque (current) to make up for the lack of RPM.

But as our motor starts to spin up and our RPM rises, our torque needs to lower in order to keep the power constant.

But to get torque (current), our AC voltage needs to be higher than the BEMF, or no current flows.

Seems like a good basis?

Off-topic I have noticed how during the day I usually in the university suck up as much information as I can, but sometimes I don’t understand the principles behind them. After a good night’s sleep though, things start to fall in place.

Power = Torque x RPM That is right.

But I’m not sure about your second statement. Power = Current x BEMF

Shouldn’t it rather be: Power = Current x Effective Voltage?

But that seems to simple too. I think you should try and derive it from first principles.

That was my first theory, but as we discussed it with Devin it turned out not to work. Because the effective voltage is indirectly affected by the BEMF/RPM , so it doesn’t work with the Power = Torque x RPM.

It is apparent in the Vedder’s video logs, as the Power he logs is much higher at higher speeds, even though the motor current is the same and that is the RPM giving higher overall power.

And BEMF is directly related to RPM.