Motor braking. - RC-Monster Forums

Trick440 · **Motor braking. -** 05.06.2007, 06:11 PM

What are the downsides of using only the motor for braking?

I heard its harder on the motor and esc, but not sure to what extent. Especially on the bigger trucks (revo, emaxx)

Serum · 05.06.2007, 06:22 PM

You can use the motorbrake, but the heavier the vehicle, the harder it is to brake.

the motorbrake means more stress on the controller, and the motor will heat up sooner. What it does is 'shorting' the wires of your motor, and the energy is stored back into your cells. (tipical way of braking with electric motors)

Most controllers can handle it though. If you tell us the setup you want to use, we can tell you if it's wise to use a mechanical brake or not.

zeropointbug · 05.06.2007, 06:48 PM

Since when are the motor brakes regenerative brakes? I thought they were just a reverse torque.

I do know it's quite hard on the esc, both the harder you brake,the weight of the RC, and gearing. Most of us use motor brakes, as far as I know.

I think this MAY have been a factor why my Quark capacitor blew, I turned the braking setting to double, very hard on the caps.

GriffinRU · 05.06.2007, 07:10 PM

Rene correct, when you apply brakes ESC shorts the windings and can do that with bursts simulating ABS...

Also each FET has a built-in diode which works as an H-bridge with other FET's, thus charging battery and cap if generated voltage higher then battery voltage( accelerating going down hill or bursts after jump). Caps usually take care business here and if connection between batteries and ESC is not good then often fail...

So, when you use motor as a brake then you put motor in bad situation because now it need to absorb kinetic energy of rolling vehicle (mv^2) and do that fast. Think, you Ok with accelerating within couple seconds but you would like to stop on a dime, right? Do the math then.
For controller it is up for caps how good they are and how good is battery connection.

zeropointbug · 05.06.2007, 07:19 PM

Really, I thought it was something a little different.

BTW, when my truck is not moving, and you apply the brakes, you can hear a buzz, like pulses. This is the Quark, i love the brakes it has, they are super smooth, and never lock up.

So I suppose these ultra caps should do an excellent job for braking.

GriffinRU · 05.06.2007, 07:28 PM

Quote:

Originally Posted by zeropointbug

Really, I thought it was something a little different.

BTW, when my truck is not moving, and you apply the brakes, you can hear a buzz, like pulses. This is the Quark, i love the brakes it has, they are super smooth, and never lock up.

So I suppose these ultra caps should do an excellent job for braking.

If they are discharged! Getting idea?

Trick440 · 05.06.2007, 07:36 PM

This is a quark 125b esc. On a Revo, w/ a Neu 1512 2000kv.

I just took it for a test ride. My first ride with reverse, and the motor brake. It was pretty sweet. I could flip it with a hard brake. Once I got use to it, I liked it.

So its should cause some more heat, but for the most part its ok to do?

GriffinRU · 05.06.2007, 08:38 PM

Quote:

Originally Posted by Trick440

This is a quark 125b esc. On a Revo, w/ a Neu 1512 2000kv.

I just took it for a test ride. My first ride with reverse, and the motor brake. It was pretty sweet. I could flip it with a hard brake. Once I got use to it, I liked it.

So its should cause some more heat, but for the most part its ok to do?

Yes, better then Ok, if motor can handle that.

05.06.2007, 08:43 PM

Are you certain the brakes are regenerative? Surely that'd be dangerous if you're using lipo packs...

GriffinRU · 05.06.2007, 08:55 PM

Quote:

Originally Posted by Aragon

Are you certain the brakes are regenerative? Surely that'd be dangerous if you're using lipo packs...

Yes, but charging will happen only when motor generate voltage higher then battery voltage + voltage drop across diode.

zeropointbug · 05.06.2007, 09:22 PM

Quote:

Originally Posted by GriffinRU

If they are discharged! Getting idea?

Why would they have to be discharged? It would be as long as the potential is greater than the battery...?

Serum · 05.07.2007, 01:21 AM

With normal caps the internal resistance is near 0 when they are discharged. you need a low internal resistance when braking.

zeropointbug · 05.07.2007, 01:31 AM

Why do you say it's near 0 when discharged? Wouldn't it be the same impedance regardless? Can you explain why that would be?

Anyways, it would never be able to be discharged.

hyperasus · 05.07.2007, 03:28 AM

Sounds like a bunch of theories. So whats the real scoop? Does anyone actually know? One thing I know for sure, Breaking isn't nearly as demanding on the controller as hard acceleration. You can say it is all you want but I know from driving my brushless trucks that it isn't. Locking up the wheels on an RC just takes alot less energy then getting the sucker up to speed in the first place.

05.07.2007, 05:06 AM

I don't think it is regenerative...

If it were, why is the braking force consistent? If it were regenerative, the braking force should be higher if your battery is flat.

Also, what stops the brakes from causing a spike that takes your lipo above 4.2V/cell?

And if it were, why do we see no hint of this on our onboard power meters?