Motor brakes or mechanical?

[E-Revonut]

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.

[shaunjohnson]

ok u got me
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

[E-Revonut]

Originally Posted by shaunjohnson

ok u got me
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

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.

[shaunjohnson]

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

[E-Revonut]

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.

[shaunjohnson]

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!

shaun

[Ryu James]

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.

DEAR MR DIRK DIGGLER

[Arct1k]

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.

[Arct1k]

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

[Ryu James]

Originally Posted by Arct1k

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.

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....

[shaunjohnson]

Originally Posted by Arct1k

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

LOL

[George16]

Originally Posted by E-Revonut

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.

First Law of Energy (First Law of Thermodynamics):

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

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.