Is ABS breaking safe for brushless systems?

[simplechamp]

Now that I have an on-road vehicle I thought I might play around with the ABS braking function on my Nomadio Sensor. My question is, is it safe for brushless systems? From what I've always read motor braking produces voltage spikes that can be hard on the ESC and lipos. So then I wonder will pulsing the brakes using ABS make this worse? Or is it OK? Or am I looking at this wrong?

The ABS doesn't necessarily mean pulsing between 0% and 100% strength. I can adjust that to whatever I want, and also the length of the cycles, when the ABS triggers, etc.

Any insight is appreciated. (Is ABS just a gimmick on this scale? Or is it only helpful for mechanical brakes?)

[BrianG]

I honestly don't know how any radio can have anything resembling ABS (seeing as how it means Anti-Lock Braking) unless it is getting tire slippage feedback. Otherwise, it's just variable braking.

Yes, there can be voltage/current spikes in any type of ESC braking. Some ESCs, like the MMM, have TVS devices that basically shunt any voltage above X value (X is usually a couple volts above the absolute max the ESC is designed to handle) to ground to protect the ESC/batteries from excessive voltages. The amount of brake force, battery voltage, vehicle speed, and weight of the vehicle will determine how high those spikes are. If you want to help the ESC cope with lots of braking, try using a battery voltage less than the ESC's max. So, if using an ESC rated for 6s, use 4s or 5s instead. The spikes will not be as high so the TVSs won't be stressed as much.

[simplechamp]

Yes, the ABS braking is a misnomer. It is variable braking, but you get the idea. I just called it ABS because that's what it's called in the manual and radio menus. Futaba calls it ABS also. I'm mainly concerned with the effect on the ESC, not so much the terminology.

I will be running a MMP on 4S, so that leaves some headroom, and the vehicle is pretty light for a 1/8 with all the carbon-fiber. I guess I'll start with the default ABS settings and go from there. It has the brake/coast cycle switching every 0.1 second and I think the coast defaults to 50% brake strength, not full coasting. The ABS is only applied at 50% or higher trigger push by default. I will have the drag brake turned off on the ESC. Not sure what to put the ESC brake strength at though?

[bigbadtaz]

what its does is the same a real ABS in full size cars it keep you from locking up the wheels it pulsate the braking servo not sure how well it will do with a esc......

[simplechamp]

Right, I understand that. What Brian was saying is that true ABS on 1:1 cars only engages when it detects the wheels are locking up. RC transmitters can't detect this, they just pulse the brakes at a certain trigger point you set, like 50% trigger push, or 75% trigger push.

[Overdriven]

The amount of braking is still going to be the same as without abs. If anything the (average) load will be decreased during braking due to the modulation.

I believe my 3pmx has it too, but I've never messed with it. I just adjust the MMM until it will barely lock the tires and/or braking is easily controlable on the highest traction surface the vehicle will normally be run on. I usually end up with 70-80%.

Does the radio manual make any mention of how to set the esc before trying abs. The amount of adjustment may be somewhat limited. I would think you'd want maximum braking from the esc though. Personally I'd try it with max braking, medium abs. Then maybe lower the esc to 90 and make more abs adjustments. At that point you will probably start getting a feel for it and can work from there.

[DrKnow65]

I default to using the ESC software for brake control, though I do use a Futaba 3PM that does all the ABS, Dual Rate, Exponential stuff.
I just think the ESC software has a little farther to come and I could vision a REAL ABS function, since it does have feedback...

[Shonen]

I tried playing around with it in both my E-Revo and Revo conversion on my 3PM-X. The E-Revo would judder, more or less violently depending on the settings, and the Revo conversion would be not very noticeable (mechanical brakes). I think to truly have a setup in need of ABS, you have to have an extremely rigid brake servo mount and a fast high-torque servo...I have neither, as I am running the stock Traxxas servo box and a Tower Hobbies TS-140.

I'm not a racer, so who knows? It may provide some benefit. All it did was bother me when I had to disable it to calibrate the ESC's I was testing with the chassis, and it does continue pulsing (squeek squeek squeek squeek) after you've come to a stop. For me it's just a novelty, it's not like my braking setup is capable of locking the wheels anyway.

I agree with everyone, try play with ABS braking and see if it's for you...just don't push your ESC to its voltage limits due to the increased number of spikes it will see.

...ABS breaking, on the other hand...

[simplechamp]

Thanks for the input guys.

There are a lot of settings I will need to play around with: when the ABS triggers, optional trigger delay, the speed of the pulse cycles, strength of both the braking and coasting portions of the cycles. It even has a setting to only allow ABS during a turn, e.g. the steering must be at 30% either direction for the ABS to engage. One very important setting is how much brake is let up on the coast cycle, the coast doesn't necessarily mean completely let off the brake, it can mean reduce brake to any lower amount.

I know it's probably not necessary, but I love the technical aspects of all the electronic RC stuff we have.

EDIT: I just looked at the DSM (Nomadio can't use DSM2) frame rate, and Spektrum says it's 11ms to 16.5ms. So if I round up to be safe that's 20ms, which is 0.02 seconds. So that means I should be able to set the brake and coast pulses down to 0.02 seconds each if I wanted. It seems the ESC should be fast enough, I am thinking the Tx will be the limiting factor. Real 1:1 cars ABS pulse cycle at about 15 times per second, 0.067 seconds for the whole cycle and 0.033 for each portion (brake/coast). So I am going to start out there and see how things go.

[simplechamp]

Now I remember why I bought the Nomadio...

I hooked it up to the computer and configured the buttons/softkeys so I have access to all the ABS features on-the-fly. I can turn ABS on/off with the touch of a button, and each ABS setting has it's own button for adjustment. Should make testing this out a lot easier.

I think what I'll do is test it like a real 1:1 cars are tested. Just get up to speed and then at a certain marked point apply full break and measure how much distance it takes to stop. Should be interesting to see the outcome.

EDIT: On second thought, I'm looking at it wrong I think? ABS is to maintain control and prevent skidding, not stop faster... well, either way I'll try the test, and then maybe work in a cornering test too.

[Shonen]

it's different onroad and offroad too, depending on the surface you will stop faster if you lock the wheels. I would do testing in the area you are running the chassis for the results to be valid. (:

[simplechamp]

It will be unprepared asphalt, just a big parking lot I plan to test my 1/8 GT in. Never really bothered to set up ABS for off-road since I only bash on grass and dirt. Maybe if I ever move somewhere with a track I would try ABS on my truggy.

[bruce750i]

Testing the braking distance sounds interesting and fairly easy to video.
I use a FSGT-3b tx and it has a on/off, slow, normal and fast settings(pulse rate). I think it helps to keep a 2wd car's rear end behind the front end during hard breaking.
Reverse is weird, pulsing the power on and off. (but it does gain speed)