Motor brakes or mechanical?

If you have two identical MT's, with the same brushless esc, motor, battery combo, which setup would be more efficient: Braking with the motor or mechanical braking? Which setup would give you the most runtime?

I'm interested in your opinions and explanations (have a lot to learn).

[Arct1k]

Well technically motor braking is more effecient - My reasoning is:

1) It is regenerative and hence puts some power back into batteries
2) You are not powering an additional servo

However it puts additional load on the esc and motor and hence due to effeciency losses they get hotter than if you had servo brakes...

[pedeboi364]

mech brakes grab way harder=mor control and less ESC strain

[Arct1k]

Originally Posted by pedeboi364

mech brakes grab way harder=mor control and less ESC strain

Firstly that wasn't the question - Apart from front rear bias - that is tosh about grabing harder and more control... ESC brakes on a modern ESC such as the MM and MMM are infinitly variable in both strength and profile...

You can easily lock up breaks on a 12-15lb MT with a MMM and ESC brakes do not suffer from fade.

Agree and noted above that ESC braking puts additional load on the esc - but provided you are geared correctly and have the appropriate setup this is not an issue.

[_paralyzed_]

Originally Posted by pedeboi364

mech brakes grab way harder=mor control and less ESC strain

I disagree. These brushless motors can brake just as powerfully as they accelerate, and both have the power to luck up the wheels, which makes the braking power equal because once the wheels lock traction is lost and no extra amount of power will help.

I prefer motor brakes. They are simpler, and mechanical brakes can heat up and fade during a race, motor braking will never do that.

[_paralyzed_]

1 min late^^^^^^^

Thanks for replying.

About the additional load on the esc: I thought pdelcastillo mentioned somewhere that because of the regenerative braking, the additional load on the esc wasn't that high at all?

Also: does anyone dare to say (and explain) that a mechanical brake setup will give longer runtime?

[pedeboi364]

lol, thnx for the correction guys

[_paralyzed_]

no one has done an a/b comparison of runtime with and without mechanical brakes, so the can only be speculation. Intuition tells me it is tit for tat, or one is no better than the other. Compared to the 100+ amp load the motor creates the small amounts of electricity used to brake is negligible

[BrianG]

Originally Posted by drkdgglr

Thanks for replying.

About the additional load on the esc: I thought pdelcastillo mentioned somewhere that because of the regenerative braking, the additional load on the esc wasn't that high at all?

Also: does anyone dare to say (and explain) that a mechanical brake setup will give longer runtime?

Well, you gotta figure it'll make the ESC heat up more since braking is "channeling" the power back into the batteries. Channeling is not "all or nothing", there are degrees of brake force. This means that the ESC is still switching on and off and you get losses from the slew rate of the FETs. If braking was in fact on-or-off, you wouldn't have these losses and the ESC would heat up less (if at all) - of course that would be quite difficult to control.

And I don't dare say that mech brakes will give longer runtime. After all, it has already been said that ESC brakes are regenerative, so if anything, you gain runtime. And even if ESC brakes weren't regenerative, you'd still gain a little runtime because of the reduced weight from the lack of brake servo, linkages, pads, disc, etc.

Another advantage, although not technically related to braking, is that ESC brakes also let you have reverse. The only way to get reverse on an mech braking setup I know of is to use a solution where the gears are switched in the tranny.

[shaunjohnson]

Originally Posted by Arct1k

Well technically motor braking is more effecient - My reasoning is:

1) It is regenerative and hence puts some power back into batteries
2) You are not powering an additional servo

However it puts additional load on the esc and motor and hence due to effeciency losses they get hotter than if you had servo brakes...

we all wish they were regenerative but they are not << edit: wrong fact it seems
even the new toyota prius and other hybrid cars dont have regeneraive brakes.
the reason being is...
applying current to the motor that has reverse timing (so the timing is -20* for instance) is MUCH more powerful than getting the motor generate current.
this goes double for brushless motors as you can only generate on one phase at a time and that means a lot of switching around just to get a few more mah.

here's a simple test...
get a brushed motor and put the shaft in the drill.
spin it over,,,so ok you feel a little resistance (like the motor would usually do when it is freewheeling), now short out the main solder tabs by some means.
you will feel the resistance increase a fiar bit but it wont lock up.
you want your brakes to be able to lock the wheels right?
well shorting out the phases so to speak is not going to work, a brushed motor...reverse current is applyed and this essentially reverses the timing allowing the motor to slow to a stop.

brushless motor's just have to reverse the timing on the phases.

shaun

[E-Revonut]

I really don't think that braking with the esc creates all that much heat. I have yet to temp my MMM at anything over 130* in my E-REVO. I have never heard the fan kick on when running either. So any heat that is created is neglegable(?) and disipated easily.

[E-Revonut]

Originally Posted by shaunjohnson

we all wish they were regenerative but they are not
even the new toyota prius and other hybrid cars dont have regeneraive brakes.
the reason being is...
applying current to the motor that has reverse timing (so the timing is -20* for instance) is MUCH more powerful than getting the motor generate current.
this goes double for brushless motors as you can only generate on one phase at a time and that means a lot of switching around just to get a few more mah.

here's a simple test...
get a brushed motor and put the shaft in the drill.
spin it over,,,so ok you feel a little resistance (like the motor would usually do when it is freewheeling), now short out the main solder tabs by some means.
you will feel the resistance increase a fiar bit but it wont lock up.
you want your brakes to be able to lock the wheels right?
well shorting out the phases so to speak is not going to work, a brushed motor...reverse current is applyed and this essentially reverses the timing allowing the motor to slow to a stop.

brushless motor's just have to reverse the timing on the phases.

shaun

Are you implying that Patrick is a liar? I will beleive him over you telling us that the braking IS regenative

[Arct1k]

I guess the maker and designer of some of the best ESC's don't know what he's talking about...

Originally Posted by Pdelcast

The braking is regenerative because it has to be -- can't dump that much energy anywhere but back into the battery. (The battery is used as a load, but using a battery as a load mean charging the battery...)

It is not, however, optimized.

Still gets fairly good efficiency up to about 35% braking power -- above that the conversion efficiency gets lower.

PS lower effeciency means heat...

[Arct1k]

PPS OOPS Prius DO have regerative braking when coasting above 7mph...

Better Gas Mileage in a Toyota Prius

http://www.hybridcars.com/gas-saving...ota-prius.html

The main idea is to control the amount of braking that is used to regenerate energy to the batteries. (Regenerative braking is essential for keeping energy in the batteries, but a little bit goes a long way. Avoiding overuse of regenerative braking will prevent you from slowing down more quickly than necessary. Extending your glides and coasts is a key to maximizing mileage.)