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).

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...

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.

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.

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?

lol, thnx for the correction guys

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

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.

we all wish they were regenerative but they are not:no: << 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

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.

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

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

PS lower effeciency means heat...

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

I don't want to start a war here but I just checked ShaunJohnson's profile. He is 16 and by the looks of it the only thing he has with BL is a VXL Rustler and he only joined the forum in November. Most likely he has missed a lot of the technical information that has been provided by Patrick and doesn't have to much experience with high powered BL systems. Of course this is all speculation on my part but as I already stated I will take patrick's word that regenative braking is used. Also I'm sure that a prius uses regenative braking as well. I built DC motors for 5 years, 5"-11" armature diameter brushed motors. The company I worked for was pretty small at about 12 employees so I was pretty well kept in the loop about what was going on ( I was one of the first few employees that helped get the company going) We also dealt with controllers for these motors, most of what we did was for golf carts and neighborhood electric cars such as GEM cars and all of them used regenative braking!

Sorry for hijacking the thread, sort of! But essentially ESC brakes should give longer runtimes because braking puts some energy back into the battery. No matter how small this amount is it is still better than a servo that will take energy to brake.

ok u got me:lol:
i was basing my info from large scale brushless/induction motors.
but do that little test with brushed motor...it's a good one ;)
i must have been wrong:yes:

rather than your test why don't you hook a lightbulb up to the motor and turn it with a drill and see what happens! Then tell me what happens with the energy that gets created by braking.

yes there is energy being created there.
but the voltage generated has to be more than the lipo's pack voltage to be doing any charging. right?

so if u have a 4s lipo the motor regeration has to be (after going through any conersions and stuff through the ESC) 14.8+v

you will get more "load" by shorting the 2 tabs on the BRUSHED motor and hence more braking than what you will if you had surplus and wanted to regenerate.
so braking power must be wasted by heat. right?

no i'm not looking for a war either..and no patric is not wrong..i am:wink:

well it takes a big man to admit that he's wrong so I'll give you credit!

Yes there is heat produced in all of this so it's not a 100% efficient. Even if it was only 1% efficient though it would still put energy back into the battery when braking rather a servo using energy to brake.

i'd like to do that test on a controlled RPM.
so brushed motor at say 20,000rpm (or operational RPM) and see how many volts are being generated.
because like i said that voltage has to be the same or more than the pack voltage.
brushless motors should be similar but i do not know what voltage the motor itself runs on (the ESC could be giving it a lot more v's that i think, since it's 3 phase and AC)

and also...the current generated is pure DC current...the power the ESC gives the motor is Pulsed DC current.
so i'm sot sure if hte FETS could take a pure DC??


look anyway...sorry for hijacking he thread, i leaned a lot, you guys leaned that i'm a bit of...well i'll let u make up them words lol.
END OF! :wink:

shaun

DEAR MR DIRK DIGGLER,

i used mech brakes for quite a while and then recently put motor brakes to the test. i didnt like the motor brakes as much and i did not notice any longer run time. if the regenerative theory is even true i dont think it amounts to anything that will give you more power or run time.

after 20 minutes of hard and fast practice on a tight track with many turns i have never noticed even the slightest fade in my setup. maybe others do with lower quality pads but if you get halfway decent pads this is not an issue. also, at the track i can take the turns tighter than anyone else running motor brakes because i am able to set bias to the rear allowing me to sort of "powerslide" into the turn...kinda like drifting. mech. brakes add a total of 2 ounces to your setup. hardly anything that will hurt you and weight you could easily makeup somewhere else by getting lighter components in other places on the car.

i think the guys that like motor brakes are guys that have never really raced with, or even tried, mechanical brakes. i was guilty of this myself against motor brakes but after some convincing arguments i tried them out, hoping i would like it. i wasnt sold.

motor brakes do have tons of power though and are able to lock up as easily as mech brakes. the difference is you cant adjust bias.

and mech brakes are definitley more efficient for your motor. with mech brakes you can have braking and reverse set to 0% so your motor is not working at all when you brake. ideally though you set your esc to about 10-20% motor braking and use mech brakes. the motor braking is nearly non existent and the brakes do most of the work....just like a real car that is a manual. to slow down you shift down and let out the clutch so the motor takes a little bit of load off the brakes. also helps to eliminate chance of brake fading.

if motor braking really was better we would all just drive our real cars without brakes and just shift down when we needed to stop. i know thats not an apples to apples comparison but you get my point.

if you want efficiency, performance, and cooler temps then you want to run mech brakes. try them both and let the proof do the talking.

:intello:

RJ - Agree 100% with everything your said - The question wasn't which is better for an experienced racer (fully acknowledge the f/r bias option with mech brakes).

The question was battery life - I'm not sure how much longer you get with ESC braking and if it would be noticeable but the "theory" backs elec has less weight, less power requirents i.e. servo, and regenerative breaking and hence should offer longer run time however marginal.

Mike has previously stated a combination of both mech and elec probably offers the "best" setup but for "most" of us bashers and "sunday" racers esc braking will surfice.

My questions were indeed related to runtime. I understand in racing conditions other things are more important.

The reason I started this thread was that in another forum someone stated that using mechanical brakes would give up to 25% more runtime compared to using motor braking. I found that hard to believe.

Must be the traxxas forum - Don't tell them about here please...

makes sense. no arguments against that. it all comes down to preference too. both setups get the job done.

Nope. I don't go there.
It was on a Dutch forum, and I did tell them about 'here'. The guy who made the statement actually is a member here. I hoped he'd step in, but he hasn't yet....

LOL:yes:

First Law of Energy (First Law of Thermodynamics):

Energy is neither created or destroyed. It can only transform from one form to another :whistle::whistle:.

Edit- I "seem" to run longer using motor brakes than mechanical brakes though the test trucks are different. My ST-RR uses motor brakes while my Revo uses mech brakes but both use the same motor and batteries.

Huh? The motor isn't "working" when you brake, it's using the battery as a load and dumping the power there. Your argument doesn't make any sense.

FWIW, I've tested this with my eagletree and I can see amperage and voltage go UP when I brake, which is proof positive of regen braking. Think of it this way, if you didn't use regen braking, where would that energy go? Where's the load to dissipate it? Surely not through the FETs. It's regen.

Have a closer read of Ryu James's sentence that you quoted. :yes:

my point is that the motor is not having to "work" to slow down the vehicle cuz the mech brakes do this. i am sure energy is still being spent in small amounts of course but the motor is basically freely rolling if you set your esc brakes to 0% and reverse to 0%. it must be working less than it would be when slowing down a 9 lb truggy all by itself, right?

No - its not "working" as a motor it is working as a "generator" and hence creating elec (and heat) from the kinetic energy of the car.

sleebus,
the egle tree probably shows a voltage increase when braking because voltage drops under load...as soon as you get on the brakes the voltage is probably picking up what it was losing under load:neutral:
but if the voltage spike was above it's "resting" voltage then i guess you are right :mdr:

No. The motor would only be working as a "generator" while you are "free rolling".

The moment you apply brake, you are asking the motor to stop a 9lb vehicle. And this comes at a cost = energy.

Do you believe that making a motor alone stop a 9lb vehicle, that it would not spend any energy doing so? Are you saying that it would actually re-gain energy making this happen?

Yes that's what he's saying. Have you read the entire thread?:rules: regenerative braking is used. You cannot lose energy, only transform it. The stable temps on the mmm esc prove regenerative braking works, otherwise your esc would cook because that stopping power has to go somewhere, either as heat on a brake disc, heat on a blown esc, or back to the battery in the case of the MMM. Eagle tree graphs prove energy is regained.

Correct it is working to stop the car - but it comes with a benefit "energy" that the motor/esc puts into the battery...

somebody, anybody, i want to see these stats that PROVE that energy goes back into your battery when you use motor brakes and i also want to see how much. is it a trace amount? or are we talking 10 extra minutes of run time here? i think it is all myth. i agree with what Marzac is saying. the energy graph shows an increase when the brakes are applied only because there was a large drain on energy when the throttle was on. i am very skeptical of the "regenerative braking" theory as it is so convincingly put. somebody prove me wrong. back up these claims please!!

Why don't you read about regenerative braking om 1:1 cars? It's the same but on a different scale. It might not be a lot but it's still there.

I remember Patrick posting about this particular topic though I'm too lazy to search.

Edit - Read this:
http://www.teslamotors.com/blog4/?p=58