esk8.news esk8 calc donate now

Is somebody riding in duty cycle mode?

Hey, I want to switch from current control mode to duty cycle mode to get the actual percentage of power instead of this little strange accelerating when you keep the throttle in one position in current control mode. But if I switch the modes I get an -8A brake signal all the time and if I brake the motors go in reverse instead of just breaking. I use VESC HW 6.6 and latest VESC tool FW.

2 Likes

I ran this for 2 minutes and it tried to kill me. You need to set the throttle ramp times to a rate that doesn’t just yeet you off the ends. If you let go of the remote it will brake with as much power as you let it and you’re gonna get tossed unless the ramp time is high. The acceleration and brake rates are time based to the faster you let it go the harder it is to ride

10 Likes

So is there no proper solution to get 50% of power, when I go 50% of throttle? I mean other brands have it also work like that.

2 Likes

Yeah there’s a huge disconnect between VESC’s and chinese esc’s (hobbywing, li ying)

Using a VX1 with speed modes on VESC, you get 100% top speed regardless of which mode. They only change the acceleration

On the chinese ESC’s each “mode” changes the acceleration AND top speed.

Weird how the VESC is lagging behind in this regard

6 Likes

my understanding is very small changes in duty cycle result in very large changes in motor current, so if you set your throttle to control duty cycle, you will basically reach your motor current limit like an on-off switch except for a very tiny range on the throttle

8 Likes

duty cycle is not a percentage of power… in this context it’s the percentage of time current is drawn from the battery. however as a failsafe the vesc won’t let you exceed the motor current limits that you have programmed — which means if you tried to use a duty cycle that would exceed the current limit settings, the vesc will dial back the duty cycle to a value that doesn’t exceed the current limit settings.

6 Likes

You can have the same on VESC if you use a Hoyt St Puck.

3 Likes

I do wonder why some people want to limit top speed electronically… Current control is a lot like a gas pedal in a car, controls power, not speed. Nobody buys a car and goes, I wish my gas pedal stopped working at 65mph. Why not just roll the throttle back to reduce speed? Actually curious what people’s opinion on this is.

8 Likes

and the reason you get braking if you try to use the throttle as a duty cycle control, is the following:

the voltage the motor sees is:

duty cycle % * battery voltage = effective voltage

for example:

10% duty * 50v battery = 5v effective voltage to the motor

the motor generates back emf voltage which opposes the battery voltage.

for example a 190kv motor spinning 1900rpm produces 10v of back emf.

if the applied effective voltage (5v) or (50v battery at 10% duty) is less than the back emf voltage (10v) or (190kv at 1900rpm)… you won’t get acceleration but rather braking.

but again, as a failsafe, even in duty cycle control mode, the vesc won’t let you exceed any of the motor current limits that you have programmed… it will adjust the duty cycle to prevent this condition.

2 Likes

I don’t know, maybe that’s just me, but I’m used to keep the throttle at one position and keep the speed at the same time. With the VESC in current control I need to readjust the throttle all the time and I find it a little bit harder to keep it at a given speed. What bothers me even more is, when I go on let’s say 30% throttle the board accelerates to top speed. Then I have 70% of dead travel in throttle and I cat’t go just a little bit off throttle to let’s say 95% of top speed. In total it is in my opinion counter intuitive. But like I said, maybe it’s just me because I’m not used to.

6 Likes

It will definitely work, just be seriously careful

1 Like

There is cruise control for that if you have a remote which support that as option.

what are your motor current and battery current limit settings when you use current control? its definitely not advisable to use duty cycle control for your throttle on an electric skateboard

120A bat and 100A per motor. I totally get your points. But what can I do to get the same throttle feeling like in a let’s say Evolve RC?

1 Like

Oh, you know what, you’re right. I’ve never considered that. I see your point now, once you hit top speed most of your throttle range is useless. I just coincidentally never ran into this because all my boards have max speeds out of my comfort zone for that board

I’m not sure VESC can mimic Evolve, their remote is like most RCs where a given throttle position directly corresponds to a given speed + acceleration.

A new control mode seems like an easy thing to implement and make a pull request to Vedder for. I might give it a shot myself, been wanting something like this…

2 Likes

Exactly and I want this! Any Ideas?

your vesc will likely not allow more than 50a or 60a bat so (firmware limited) so the 100a bat setting is useless…

i think if you set 50bat and 50motor you’ll have throttle range at all speeds because you’ll be assigning the max throttle as 50a motor, and based on the 50a battery setting, you’ll be able to sustain this across the full speed range.

right now your max throttle is assigned to 100a motor current in current control mode, but since the firmware won’t allow more than 50a or 60a bat, your throttle range, torque and motor current decreases with increasing speed

1 Like

So would the idea be that, if you have, say

  • 50A motor current
  • max calculated speed of 50km/h based on pulley ratio x wheel size x motor kv x battery voltage

Then, when the trigger is at 20% (1/5th of total travel), the board would accelerate at 10A motor current up to 10km/h ? And, to not have the top end have high acceleration + high speed = recipe for disaster, the ramping time constants would apply, so that it goes from the previous acceleration value to the new one in that time.

Is that how it should work?

That’s not how it works. We pull 120A from the bat at 200A total motor current. We can’t go to 50A.

1 Like