Motor braking.

[BrianG]

Originally Posted by zeropointbug

So, then, can 'potentially' all the energy from momentum be put back into batteries IF voltage is high enough through rectification, or can only half be utilized, with diodes?

This is the part I am still stuck on.

Maybe we should get an esc engineer representative on here to explain how there controller braking works. Maybe from CC, or S&T?

I'm sure some of these theories are correct in way, but whether engineers use them or something diff, who knows? just a thought

I highly doubt that. To get the truck moving it takes X energy. All that energy taken from the batteries does not make it to the wheels because of losses in the batteries, ESC, and motor. The same is true for taking motion and converting it to electricity; there will always be losses. So, you will never be able to take full advantage of kinetic energy.

[BrianG]

Originally Posted by zeropointbug

Simple and short, my opinion on braking.

BL motor braking: (most likely mechanics)

first: a shorted motor has incredible resistance from turning, and, the faster it spins, the more resistance it has.

- Using full motor shorting for braking would undoubtedly flip an R/C car over it's lid with ease.

- So, you need to control this shorting in order to control the motor shaft resistance, to create an average resistance or torque.

-Along came PWM... the controller sets up the FET's to unify all motor phases to create a short. So the controller will change PWM duty cycle depending on throttle position... so anywhere between say 1% to 95% (for ABS, guessing) duty cycle for proportional braking.

-These latest controllers (like the Quark) most likely have some good algorithms for braking.

This is just my simple theory on motor braking, not going into detail what happens in FET's.

:025:

Thanks ZP. I was questioning if the motor phases, when shorted, would have enough braking force. I took a 10XL hooked to an emaxx tranny and attached a drill to the output shaft. I turned the drill on to spin the motor. The drill I used is rated for 3600rpm (assuming unloaded). Working backwards from the tranny (1.722:1) and spur/pinion (51T/14T), the motor was spinning around 23,000 rpm, which was pretty good to emulate the real-world speed of a vehicle.

Anyway, when I shorted the motor phases, the rpms of the drill dropped considerably, but didn't seem enough to support the idea that this braking force would flip a truck or provide adequate braking force for a heavier vehicle (~10lbs), let along using PWM to control the braking force, which would reduce it. That's why I was thinking that maybe the ESC was locking the rotor in a controlled fashion.

Of course, locking the rotor would probably be extremely bad for the ESC and batteries, but it was just an idea.

Also, I fully understand the theory on PWM. ;)

[Serum]

Is it not a good idea for ppl agree with me?

If you read my post better you would not post this question.
Selective reading abilities?

[Serum]

That's a nice experiment Brian; i would say the drill would stop; here is my experience with shortening the wires;

shorted the wires, put the shaft in the drill, and i was able to deanodize the motorcan with schotch brite; it was allmost impossible to hold the motor by hand, while my drill was doing a good 3000rpm.

[zeropointbug]

Originally Posted by Serum

If you read my post better you would not post this question.
Selective reading abilities?

It just sounds like your saying it's not wise to agree with me, i read it.

[zeropointbug]

Brian, did you short all motor phases? I would have thought it would make more of an impact. How big was this drill anyways? :005:

I will do a few experiments myself.

[BrianG]

Which motor were you using and what rpm was the drill Serum? Like I said, I had the drill geared up through the tranny and it just slowed down, but didn't stop the drill. I first started by hooking the drill directly to the motor shaft and found it fairly easy to stop just by holding the motor bare-handed. Maybe my motor was not up to par??

[zeropointbug]

Originally Posted by BrianG

I highly doubt that. To get the truck moving it takes X energy. All that energy taken from the batteries does not make it to the wheels because of losses in the batteries, ESC, and motor. The same is true for taking motion and converting it to electricity; there will always be losses. So, you will never be able to take full advantage of kinetic energy.

Minus losses...

I meant whether or not you can only get roughly half (half wave rectifiy), or full bridge rectification? As it would be a sine wave generated, correct?

[BrianG]

Yup, made a Y adaptor out of 12GA wire and used some extra connectors and connected all three phases together. Shorting just two of them resulted in a "detented" feel to the resistance.

The drill was nothing special; just a 3/8" drill. I think it was a 3/4hp rating.

[BrianG]

Originally Posted by zeropointbug

Minus losses...

I meant whether or not you can only get roughly half (half wave rectifiy), or full bridge rectification? As it would be a sine wave generated, correct?

lol, leapfrogging posts!

I believe it would be full-wave rectification. Each phase would need two diodes for this, which the FETs supply depending on how they are turned on. The result would be a signal that would look like the lower center part of the picture below (borrowed from ntd-ed.org):

[zeropointbug]

Yeah, exactly. Does it have enough diodes though for this?

I just tried out motor shorting with drill, i used a 3/8 drill on 7XL, all I did was popped some 5.5mm female plugs on motor plugs and held them together. I spun the drill up and then pushed them together, good spark, but rpm's dropped by about 40%, which is alot considering. It was hard to hold onto as well. The motor was slowly getting warm, I did it for about 10 seconds. The connectors were getting very warm, almost hot, probably because from the resistance from them touching only very little.

Also, when I stopped the drill, it stopped almost immediately, normally is spins down a while...

From what I observed, it was far more than enough to flip a MT over, and easily stop it.

[Serum]

Yeah, the motor i deanodized was a 7XL as well.

[BrianG]

Hmmm, even geared up through the tranny, I didn't get that much resistance. My drill also stopped pretty quickly when I removed the power, but there is a lot less inertia in a drill than there is in a 10lb truck moving at 30mph. Maybe it has something to do with the fact I used a 10XL, and you guys used a 7XL.

[zeropointbug]

I find that strange because you would think a 10XL would have more resistance.

How exactly did you de-anodize it without getting it into the motor windings? Would i be able to do it with my 540C 7XL?

[BrianG]

If I read his post correctly, he was using a scotchbrite pad to hold the motor and the abrasion wore away the anodixing off...