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Do electric cars have brakes? - 2/24/2008 10:51 AM   
AuRora41


 

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Status: offline 		Because I've used a Traxxas Rustler and an xray M18MT, and in the manual it says they have brakes but they only go forward and backwards.

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RE: Do electric cars have brakes? - 2/24/2008 10:58 AM   
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Status: offline 		they dont have real brakes but some esc have it setup so when you push the trigger forward it will lock the engine which acts like a break. while others only lock the tires for a second and then kick in reverse.

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RE: Do electric cars have brakes? - 2/24/2008 11:17 AM   
AuRora41


 

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Status: offline 		When I hold the car of the floor and brake the wheels do stop, but when its on the ground, it doesn't look like it has any brakes at all.

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RE: Do electric cars have brakes? - 2/24/2008 12:59 PM   
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Status: offline 		Yah the ESC will break for a split of a second, then pushing the trigger back once more will put it in reverse mode. It wont lock the wheels until you let it go loose so to say.

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RE: Do electric cars have brakes? - 2/24/2008 6:46 PM  1 votes
Bigshades


 

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Status: offline 		The XL-5 in your rustler does have brakes. When you let off the throttle, push back on the trigger, and it should brake. if you push back again (a second time), it should go into reverse unless you have selected a different throttle profile.

An electric ESC brakes by shorting out the terminals on the motor. This causes a magnetic opposition in the armature, which slows it down. THUS, electric brakes are only as strong as the magnets in the motor. This means that the motor is the only thing that can slow it down. If the motors magnets are weak, such as with the stock 12t motor, it will not brake well, or "hold" very strongly.

Years ago, some ESC's had another method for braking. they applied a very slight opposite voltage to the motor to brake. this would cause an even stronger braking force, and did work very well. the only problem was that it would place much stress on the ESC, motor, and battery.

Yes, these ESC's have brakes. but with cheap motors, they will probably not be able to stay completely stopped. but in most applications, this will not impede performance at all. in racing, you dont come to a complete stop, you want to slow down for a turn!

hope that helps! cheers!

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RE: Do electric cars have brakes? - 5/6/2012 4:13 PM   
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Status: offline 		So I have a question. I just bought a RedCat Caldera 10e truck and I was wondering the same thing.  Do I have to press the trigger all the way forward instantly (direction of reverse), just let go of the trigger, or barely press the trigger forward (direction of reverse) and then release it to "brake"?  I was worried about this because I didnt wanna grind the gears (or whatever, I'm ignorant when is comes to how RCs work!) or blow out a motor or any other part.  I just wouldn't think triggering reverse when my trucks at full speed, or any speed for that matter was good for any of the components.  Anyways, I'd appreciate any input, thanks.

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RE: Do electric cars have brakes? - 5/6/2012 4:26 PM   
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Status: offline 		using the brakes is not going to hurt the car, actually mechanical brakes are more dangerous if they are set up too strong because you are locking the pinion in the diff, set too strong and you have enough grip you can sheer of teeth.

going in reverse while going forward is only going to make the car spin out because it simply cannot grip.

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RE: Do electric cars have brakes? - 5/6/2012 7:36 PM   
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Status: offline 		Electrical brakes actually charge the battery! They can be so strong as to make the car flip. They are very effective, with the one and only disadvantage being that they can only brake the entire drivetrain applying the same stopping power to the front and rear wheels, not independently, as mechanical brakes can. I giggled the first time I accelerated my Flux and then tested the brakes, it went rolling down the road doing multiple endos like some crazy somersaulting clown.

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RE: Do electric cars have brakes? - 5/6/2012 7:44 PM   
The_Shark



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quote:

ORIGINAL: Foxy

Electrical brakes actually charge the battery! They can be so strong as to make the car flip. They are very effective, with the one and only disadvantage being that they can only brake the entire drivetrain applying the same stopping power to the front and rear wheels, not independently, as mechanical brakes can. I giggled the first time I accelerated my Flux and then tested the brakes, it went rolling down the road doing multiple endos like some crazy somersaulting clown.


i still favor mechanical brakes so long as they are built well enough they don't fade.

electronic brakes are CRAZY with brushless, I think the brakes on my Group C is set to 20% and even that is able to make the car hop to a stop.



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RE: Do electric cars have brakes? - 5/6/2012 10:01 PM   
Cronniss


 

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Status: offline 		Ok, lemme see if I get this straight...

On electric cars, the ESC will provide the braking power needed by essentially reversing the motor for a moment.  With some ESCs (not all) the power generated with the reversal of the motor will actually charge up the battery.

Now, if that's true...

Since the "brake" is only applied for a moment, wouldn't the resulting charge be negligible?  And isn't braking in that matter hard on the motor itself?  Or do I have that wrong?


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RE: Do electric cars have brakes? - 5/6/2012 10:31 PM   
Foxy



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Status: offline 		No, you're not wrong, the gain is negligible, but look at it this way, when you brake you aren't using any power. As for straining the equipment, hard to say, I doubt it, they probably have some means of handling the surge, but I really don't know.

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RE: Do electric cars have brakes? - 5/6/2012 10:53 PM   
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Status: offline 		I have been wishing (and waiting) someone would make a manual front brake kit for 1/10 2wd electrics.

There are real disk brake kits for 1/5 gasoline powered RC's. Basically, its a disk rotor like on your real car with a cable (like on a bike) that goes to a servo.
There are hydrolic brake kits for 1/5 RC's as well tho.

But electric rc's use the speed control to lock up (or slow down alot) the motor...which acts as braking. Once the wheels have stopped, then the ESC will engage reverse. Some ESC's have delay between braking and reverse (to save the drivetrain from shock) while others can go from brake to reverse quickly.
ESC's for rock crawlers can go right from forward to reverse.

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RE: Do electric cars have brakes? - 5/6/2012 10:58 PM   
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quote:

ORIGINAL: Foxy

Electrical brakes actually charge the battery! They can be so strong as to make the car flip. They are very effective, with the one and only disadvantage being that they can only brake the entire drivetrain applying the same stopping power to the front and rear wheels, not independently, as mechanical brakes can. I giggled the first time I accelerated my Flux and then tested the brakes, it went rolling down the road doing multiple endos like some crazy somersaulting clown.

yes... when that happened to me I almost cried cause the body I spent 7 hours painting, and detailing pretty much got destroyed in 25 seconds
that flip also got ground down the body mount post to the point it was smooth, and the body clip was destroyed even as what was left looked like it was held up to a grinder (was on concrete)

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RE: Do electric cars have brakes? - 5/7/2012 8:44 AM   
Foxy



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Status: offline 		Yeh, me too! Savage body post ground flat instantly. lol.

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RE: Do electric cars have brakes? - 5/7/2012 1:40 PM   
phmaximus



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quote:

ORIGINAL: Foxy

Electrical brakes actually charge the battery! They can be so strong as to make the car flip. They are very effective, with the one and only disadvantage being that they can only brake the entire drivetrain applying the same stopping power to the front and rear wheels, not independently, as mechanical brakes can. I giggled the first time I accelerated my Flux and then tested the brakes, it went rolling down the road doing multiple endos like some crazy somersaulting clown.


Sorry bud, I respectally disagree, Using the brake does NOT charge the battery.... The brakes work by reversing the voltage ever so slighly and consume battery power. easly proven with a mulitmeter... Some people conect relays to the motors + & - wires so when the current is reversed it triggers brake light.
Thats why on larger R/c Electric conversions most people recomend retaining the mechanical brakes to get longer run times and braking generates heat... and on some 1/5 brushless conversion heat is a huge problem.

Just coasting is when it has a possibility of charging the battery... but u never get back the power u used to get it coasting.

Both mechanical & electrics can be great.... The best is hydralic mechanical brakes with a brake disc on each wheel.... One of the biggest flaws with non hydralic brakes is if u loose traction on 1 front & 1 rear wheel u loose all braking force.... ever seen a touring car wheel go backwards under heavy braking on low traction surfaces. one advantage of mechanical brakes, u can adjust the front to rear bias. one advantage with electric, u can adjust the innital brake force


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RE: Do electric cars have brakes? - 5/7/2012 2:49 PM   
Foxy



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Status: offline 		I beg to differ...

Here it is from the horse's mouth (Patrick Del Castillo of Castle Creations). Of course this may not be vaild for some controllers, but I understand it is the market standard. In other words, it would be more difficult to prevent this effect than to encourage it.

quote:

Well, the braking is regenerative. What happens is as the controller "shorts" a phase (by turning on the low side MOSFETs,) a current flows through the phase (with that phase acting as a generator.) When the MOSFETs turn off, the current wants to continue to flow (because of the phase inductance.) Now, if you remember from electronics classes (when you built that relay based "shocker" to zap your friends with high voltage using only a D cell battery) current in an inductor will do what it has to do to continue to flow, including boosting its own voltage. So, the inductor voltage rises, and then flows through the body diodes of the FETs, and back to the battery. (very similar to the way a "boost" switching power supply works)

We dont brake synchronously in our hobby controllers, so the regeneration efficiency is not as high as it could be, but it's still not bad. The only issue is that you can make the temperature rise in the controller by driving the brake for a very long time.


Wikipedia on regnerative braking systems... http://en.wikipedia.org/wiki/Regenerative_brake

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RE: Do electric cars have brakes? - 5/7/2012 5:01 PM   
proanti1



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Status: offline 		Electric brakes (drag brakes) work by shorting the phases together, or what is sometimes called a 'loose step'.

This is the circuit that does it. The motor basically becomes an inductor.

It's similar for brushed ESCs, but a bit more complicated, as it dumps through the mosfets.

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RE: Do electric cars have brakes? - 5/7/2012 7:16 PM   
The_Shark



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Status: offline 		While im not 100% on the circuitry, i always imagined it as both poles (or phases of the stator) are pulsed at the same time, so the motor resists rotation in either direction

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RE: Do electric cars have brakes? - 5/8/2012 4:04 AM   
phmaximus



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Status: offline 		Hummm ok.... might test this....

So if I strap my Slash to a electric treadmill, then build up some speed using the treadmills motor, if I apply the brakes on my slash there should be a drop in amps and maby a increase in volts... right?

ok im wrong ive been reading more.... thanks guys, Well its true u learn a new thing each day

so in basic terms, the ESC stops providing the motor with power and shorts the + & - leads of the motor And the brake force is dertimend by how manny times per second it does this?


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RE: Do electric cars have brakes? - 5/8/2012 8:08 AM   
Foxy



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Status: offline 		Nobody isn't saying the effect isn't negligible, but it does exist. In the most simple physical terms, when it brakes, it converts the forward momentum of the model back into energy. To be honest, it's anecdotal, that's why I put the 2 exclamation marks when I wrote it above, its just a bit of fun, it doesn't mean much in the real world. I even laughed the first time I heard it being mentioned as an advantage that electric brushless conversions without mechanical brakes have over those who use mechanical brakes. Which is ridiculous of course.

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RE: Do electric cars have brakes? - 5/8/2012 5:51 PM   
The_Shark



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Status: offline 		I know if you spin a brushless motor fast enough, it does produce electricity.

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RE: Do electric cars have brakes? - 5/9/2012 2:50 PM   
phmaximus



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Status: offline 		First test....

Well playing around with a Slash 2wd 23t pinion 86 spur with a Yeah Racing Version 1 35a ESC and a Yeah Racing 3900kv motor (same as ezrun) stock bf goodrich tyres.... 0% drag, 100% brake force, 0% inital brake force

I set it up on a electric treadmill at about walking speed maby a bit more? Ill be more exact soon with a speedo

Well u guys are right just sitting there it uses 0.50a... with gyro & servo unpluged (still running 2 30mm tornado fans, ESC and reciver)
When I apply the brakes to about 50% it dropes to 0.48a then at 90% brakes it dropes to 0.46a...so far so good. here is the strange part... with 100% braking force it goes to 0.51a... mind u i have to puch the car down to keep traction.

any idear why the amp draw goes up with 100% braking? it constantly went above idle by 0.01
with this low speed test there was no differance in voltage


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