Motor braking.

[BrianG]

So, I am correct that the FETs simply apply a controlled short to the motor? If that is the case, how can the voltage develop across a short (aside from FET rdson) to get any higher? I'm not disagreeing or arguing, just trying to understand how the braking works. The rest seems relatively easy from a macro standpoint...

[GriffinRU]

Originally Posted by BrianG

So, I am correct that the FETs simply apply a controlled short to the motor? If that is the case, how can the voltage develop across a short (aside from FET rdson) to get any higher? I'm not disagreeing or arguing, just trying to understand how the braking works. The rest seems relatively easy from a macro standpoint...

If controller doesn't open FET's then BackEMF from motor will be rectified by built-in diodes and will be charging battery, if battery voltage will be less then backEMF+voltage drop. You can optimize this process if you open FETs in sync with diodes, then you will cut off diodes voltage drop and losses.
If you noticed braking can be done with only one side, while recuperating involved both.

[silentbob343]

Quick question;

Would the ABS type of braking be more or less stressful than std. proportional braking?

[GriffinRU]

Originally Posted by silentbob343

Quick question;

Would the ABS type of braking be more or less stressful than std. proportional braking?

I don't think so, should be no difference as long as ESC can handle it.

[Serum]

No, i don't think so; an ABS is just a way of braking, with the intention not to lock the tires. A gentle finger on the brakes does the same.

[silentbob343]

Originally Posted by Serum

No, i don't think so; an ABS is just a way of braking, with the intention not to lock the tires. A gentle finger on the brakes does the same.

Yeah I was just wondering if an on-off pulse from ABS would be better.

[Procharged5.0]

Someone with an Eagletree and ABS will have to run tests for us on this!

[zeropointbug]

All motor braking is switching, it does switch on/off to create braking and not just short the motor and flip the car. I probably uses simple PWM with all three phases in switch at same time.

Procharged: We discussed that braking is a loop circuit with batteries NOT included. what are you going to pick with Eagletree?

[Serum]

I guess you missed quite a bit then zero..

batteries ARE included...

for the tenth time; where would you stuff your energy needed for braking? in the esc?

[zeropointbug]

what the.... the MOTOR takes the abuse, batteries are not involved with braking. Did you miss everything that was said? :032:

Serum, grab a brushless motor and give the shaft a spin. Now connect all three motor leads together and spin it again. Notice how much stiffer it is?

Now in that scenario tell us in what battery or ESC the energy is "being stuffed"?

[GriffinRU]

Most of it will be absorbed by motor, some by batteries...

It would be really hard to measure with eagletree what's going on with braking with normal approach, but if you add current sensor on one of the motor leads then you can measure what we are looking for. But to make it clear what has more or less harm ABS or proportional braking would be still difficult. And even with the last one it would be impossible with eagletree's resolution to see anything useful...

Originally Posted by GriffinRU

And even with the last one it would be impossible with eagletree's resolution to see anything useful...

What resolution do you think would be necessary? My DPR can sample at upto 20 times per second (I think), and it is capable of measuring current flow in both directions...

[GriffinRU]

Originally Posted by Aragon

What resolution do you think would be necessary? My DPR can sample at upto 20 times per second (I think), and it is capable of measuring current flow in both directions...

Much faster, at least 2 times faster then number of PWM steps times switching frequency.

Originally Posted by GriffinRU

Much faster, at least 2 times faster then number of PWM steps times switching frequency.

I checked the spec sheet and it can go upto 5000 samples per second in high resolution mode. Surely it has to capture _something_ if it is there, even if it is recorded intermittently...