Idle speed

[fransoa]

Hello,
We are working on a true all-terrain electric vehicle with a Tesla large drive unit and a complete Tesla battery.
The result is very interesting and the performance really amazing.
In road use we have no particular problems.
In difficult terrain we use the "idlespeed" function in "nobrake" mode.
Set up with a speed that can be modified between 0 and 300 rpm with a rotating button on dashboard (can bus), making it easier to start uphill and cross obstacles smoothly. The problem is that on the descent we lose this very well speed control for a braking force regulation unsuited to low speeds. Whatever our settings, below 500 rpm the inverter releases the engine brake which goes against our need for speed control.

I searched the source code which prevents to control the braking speed below 500 rpm without finding.
This need is essential for us and if you have anything to provide me about it I am very interested.

Ideally we would need a real operational cruise control to hold the vehicle in descents and operating at low speeds (0 to 1000 rpm).
I tried the cruise control once, fortunately I was at very low speed on a straight road: the vehicle started to accelerate fully until I jumped on the brakes…

Best regards,
Francois
AVS

[arber333]

The parameter you search for is called "brkrampstr". It marks a frequency where regen slip will be reduced linearily. This prevents undesired power surges at low Hz. If you would have 3Hz slip at 5Hz rpm you would get almost 100% torque from motor capability. That does not translate well to drivetrain!
You may experiment with it, but for road use i have it set at 40Hz since below regen torque is too strong to be comfortable. Also with snow and rain for street you have to be carefull with your braking...

[fransoa]

Thanks for your reply.
I'll work again on this setting. Our problem is more to keep the engine brake below 500 Hz than to reduce braking at very low speeds.
However, this ability to reduce low-speed braking is necessary if the engine brake is important to avoid blocking the wheels.

[johu]

Yes idlespeed only provides positive torque, not negative. So when coming down from higher revs the car would actually accelerate once it hits idlespeed.

With idlespeed disabled the braking force is only limited by brkrampstr like arber says.

Maybe try the idlemode=cruise setting and connect a switch (or can bus signal) to the cruise control input. Then just disable idlespeed when descending. It may also be worthwhile to connect pot2 for regen force regulation via pot.

[fransoa]

Thank you for your information.
I tried pot2 on a knob: the problem of speed control reduced downhill does not change at all.
I tried the cruise via the CAN bus: I carried out the test at low speed. For some reason I don't know the engine has accelerated to the full... very surprising with a large drive unit ... the brake stopped the phenomenon and I'm hesitant to do it again! In addition my wish is to define via the CAN bus the speed to maintain. The ideal, after doing many tests, would really be that idlespeed regulates the speed also to brake in my opinion

[johu]

Yes setting cruise speed via CAN sounds like a good idea. Would still need to know why it accelerated hard when you enabled cruise control.

[fransoa]

I really hesitate to repeat the cruise control test...
In any case, I cannot change the value of cruise control by CAN bus, because the goal is the current speed of the engine at the time DIN_Cruise switches to 1 (CANIO or input).
I dynamically modify idlespeed by CAN bus for my tests : It's really good and would be perfect if this speed was contained downhill.