This must be a newbie question, but I haven’t come across a definitive answer yet.
My configuration - Chinese 250W BLDC motor connected to VESC (v2.18 firmware) with Hall sensors supplied by a juicy 22.2V cell pack
PPM input as throttle control and it was verified to cover the full range (0 to 100%) when displayed on BLDC Tool.
Question - When freewheeling downhill, I want to be able to apply a variable amount of braking instead of simple on/off. Is that possible with a PPM throttle? I have tried tuning the “Motor min (regen)” and “Batt min (regen)” current limits already, but it made no difference.
If regen braking cannot do it, are there other methods?
Supplementary info - When I used PID speed control, variable speed propulsion forward and reverse was totally achievable.
Vesc is progressive braking unlike RC escs. Post up your motor min and battery min amperage settings, and your weight and setup etc…
Also you should be running Current Control with brakes, no reverse optional.
Yes, it does variable braking by default.
Snapshot of motor control settings
Motor max 60A
Motor min (regen) -10A
Batt max 60A
Batt min (regen) -10A
Absolute max 130A
Already in “Current no reverse with brake” mode.
Physical configuration: single motor direct drive
Body weight 55kg
What other info is needed?
Thanks for a speedy response.
set your motor min to like -40 or -60.
Depending on your battery, you may also want to increase your battery min by a little too.
Be aware that if you have a nearly full battery, on a long hill, you may reach an overvoltage on the battery, at which point the brakes will cut out.
In that case I must have missed something in the settings. The braking right now is just simply on/off.
I want to be able to coast downhill with speed control. Too much to ask for?
It really isn’t just on/off. Increase your minimum barking current and try again.
Oh yes, the full battery issue was already explored, but that wasn’t the reason.
The power pack I have is spec’d at 7500mAh at 22.4V. It does propel uphill quite well.
What type of battery specifically? Lipo? Li-ion? What brand?
“Increase minimum braking current” means more -ve. Right?
I need more details on your battery first.
The battery pack is made up of a bank of 18650 cells wired in a 6-cell series, with up to 3 packs in parallel.
These cells are Samsung Li-ion ones.
I have also tried a 22.2V Li-Po pack, but it made no difference.
What Specific samsung li-ion cells are they? What does the text on the wrapper say?
Those cells are only good for about 10 amps each discharge, and 2.5 amps each charge. With a 6s3p. that means your maximum safe battery current is 30 amps, and your maximum regen current is about -7.5 amps.
This is far from ideal for an esk8, it severely limits your available power, as well as your available braking current, which may be contributing to your braking issue.
If you plan to continue using this pack, set your vesc as follows:
Motor max: 60
motor min: -40 to -60
batt max: -30
batt min: -7.5
You will have good braking at low speed, but it will be crappy at high speed, and the only way to improve this is to use a battery that can handle a higher charge current (Battery min)
I knew that these cells are reasonably cheap and the chemistry is a bit slow to charge, but they do yield a decent peak current.
What if I am happy to burn the power off instead of regen, would that give me more control on the variable braking? I suspect that this is kinda undermining the VESC design.
Unfortunately, to my knowledge, the vesc is only able to “burn off” power when braking at 100%, and only at low speed. More than that would cause the vesc to blow up.
I can tell you that with the exact same settings that you have there, with the exception of a higher battery minimum (and batteries that can handle it), both of my previous builds had smoothly variable braking.