Brakes Fail On Steep Downhills

Hi, I’ve been building and riding eboards for around 5 years and today I encountered an issue I’ve never dealt with before. I was riding down a steep hill, probably going around 5-10mph (I was worried about the potential consequences of brakes having issues on steep hills and not being able to save myself) when my brakes suddenly failed around half way down the hill (about 20ft down the hill). Ive never had this issue before and am assuming that the culprit is my vesc settings. I have dual 170kv 6384 motors and a MakerX DV6 vesc, paired with a Panasonic 21700 12s4p battery. What should my Battery Max, Motor max regen, and absolute max current settings be? Im guessing the vesc wasnt programmed to handle the current spike(?) from a steep downhill with the brakes on at ~90%, but I’m not entirely sure. Any wisdom or advice would be greatly appreciated, thanks in advance for your help!

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Was the battery near full charge? I also probably wouldn’t mess with absolute max current since I haven’t seen any issues at default.

My brakes haven’t failed me while going down 42% graded hills and I’ve made sure not to brake at full power. But if you can, explain “brake failing”. Like does it just stop working and cause you to continue movement?

And what is your current setting on the dv6?

by “brake failing” I mean that my brakes will suddenly cut out and I will be going downhill with no brakes. I will have to plug the board into my laptop and run the vesc tool tomorrow and I will get back to you on the current settings. Though I do know that I definitely changed it from the default so maybe the issues lie there.

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Best to check before re-running. It saves a lot of trouble.

Sorry for the delay, family complications slowed things down a bit. I just sat down to work on the board and hopefully work out (some of) the kinks. I tried to attach screenshots of my RPM and Current settings below, but I get a “host mismatch” error every time. Hope it helps, I’ve run into a wall of sorts with this one, I’ve never had this issue before with any of my prior vescs, programs, or motors before so I’m more or less at a loss with this one. Any help, suggestions, or potential fixes are more than welcome!

Motor Current Max: 70A

Motor Current Max Brake: -70A

Absolute Maximum Current: 70A

Max/ Min Current Scale: Both at 100%

Battery Current Max: 35A

Battery Current Max Regen: -20

(Both sides of the vesc have identical settings, duh🤣)

Max ERPM: 35,000

Reverse ERPM: -35,000

ERPM Limit Start: 80%

(Hope that helps in place of a screenshot lol, sorry I’m not techy enough to figure out the error message)

Oh I see where the problem lies. If you limit your erpm that low, your board will shut down. Don’t do that.

My recommendation would be to reset the esc, but do not change erpm limit from what it is. You’re not going to enjoy what happens when you do.

Cant I just use the “read default settings” button instead of restarting it? The motors seem to top out around 40k rpm, should my limit start be closer to 90% or are you referring to the Max ERPM setting instead of the limit start?

Both. I would not recommend limiting erpm at all. What you’re basically doing is turning off your esc after going at a certain rpm. The erpm shuts the esc down will not return until you return under the erpm limit. Basically, just you going down a hill will trigger it.

If you hit read default and it resets back to its original numbers, then all is fine and you don’t need to reset.

I learned my lesson when I played with the settings.

Would ERPM have anything to do with why my board cuts out when accelerating hard from a dead stop? If I pin it from a stop it’ll accelerate for a second and then one or both of the motors will cut out for a fraction of a second. Yet another problem I haven’t encountered before and I’ve been going through all the settings to find the culprit to no avail.

Yes. It’s reading your output electronically. If you go above erpm limit, it will shut the motor off and wait until it gets low again.

Erpm limit is something you do not want. In an old esc, the limit was 60k for vesc 4 based. Vesc 6 based is 100k or 150k limit (so I’ve read).

That’ll make your blood rush. Had it happen to me on my Kaly, brakes cut out going down a steep hill with a short wall at the end. Luckily I able to stop. In my case it was the bms cutting power

I changed the battery current max and max regen limits as well as updated the motor current max brake. I increased the battery max regen from -20A to -25A and decreased the battery current max to 20A. I can run 70A to each motor, and I dropped that from the 70A I was running to 65A. I have 65A set for both my motor current max and my motor current max brake settings (motor current max brake is -65A of course, not 65A). I also had the traction control setting enabled and had it set to activate whenever there was a 3000 ERPM difference between the two motors. I think that could be responsible for the sudden power cutoff to one of my motors whenever aggressively accelerating or braking hard. The torque my Motors generate makes it very easy for one of my motors to slip and rapidly increase RPM for a split second if I go over a pebble while accelerating or lose traction and lock my wheels when braking hard. Regardless, I haven’t had a problem since updating the settings listed above. I hope this helps anyone else having a similar issue, that split-second power cutoff can be a big problem while riding if you’re not expecting it. That said, I’m not entirely certain which setting/ combination of settings listed above solved the issue. Happy riding and stay safe!