What determines ESC starting speed?

[butchalline]

I have a need for an ESC (with or without BEC or brake) that has the lowest starting speed in forward and reverse. Most of the ESC's that i have start at hundreds and even thousands of rpms. I assume this depends on the motor load and other factors, so...

1. Are there any published data or tests on this subject?

2. What are your personal experiences or recommendations?

Any and all help appreciated.

 

[JatoTheRipper]

I can't answer this, but I've wondered the same so I'll be watching this thread. Good post.

 

[durok]

From a completely uneducated standpoint, I can say my CC Mamba X ESC / Holmes Revolver 1800kv sensorless brushless motor combo will crawl at such a slow speed that I can watch the motor rotate incredibly slowly.

It's an outrunner, which means I can see the outside of the motor housing spin while driving my Bomber (which has no interior).

Here's someone's YouTube video where you can see what I mean:

https://www.youtube.com/watch?v=PNoPTKE6mCw

 

[Ty@Tekin]

Both motor and ESC can affect the lowest start RPM. The switching frequency of the ESC, the number of poles and slots in the motor, the strength of the motor magnets and the motors' internal resistance all play a part.

As far as published data on ESC start RPMS, I have never seen anything before.

 

[durok]

Both motor and ESC can affect the lowest start RPM. The switching frequency of the ESC, the number of poles and slots in the motor, the strength of the motor magnets and the motors' internal resistance all play a part.

As far as published data on ESC start RPMS, I have never seen anything before.

I will state here that the Holmes Revolver has a 14 pole 12 slot stator, which has got to contribute to the high torque and fine low-speed control of the combo...

 

[Greatscott]

What kind of load are you going to have on the motor when it starts?

 

[butchalline]

Greatscott: The load would be virtually zero. It will be used on a boat, so the starting load would be only the inertia of the motor, shaft and prop. And the motor would be brushed with gearbox reduction to 550 RPM max.

 

[Alka]

With a brushed motor it's really just friction that is holding you back. If you start applying linear power from 0 volts nothing will happens until the motor produces enough torque to overcome it's resting friction. By then it is getting enough power to spin at hundreds of rpms once it's not 'stuck' . With a load it's the same thing really. Although a loaded down motor will not spin up as fast once friction is broken. Higher kv motors will spin much faster after the friction is broken and will require a higher power level to get the same torque to get going.
Some ESC manufacturers have a minimum power level on startup but with brushed motors it is not necessary.
You can normally reduce speed once it's spinning.

For brushless motors it's a whole other can of worms why they need a minimum rpm. That is to create enough back emf to determine the position of the rotor.

 

[JohnRobHolmes]

On a brushed motor, we are looking at an interaction between the motor detent force, and the minimum PWM of the ESC. In almost all cases, rough startup is just low quality ESC design. Once we get a "nice" ESC with lots of low end PWM granularity, then we can begin refining motors for better startup.


The hobbywing 1080 (all china made) is a good budget choice with decent startup. My BRXL (higher cost, all USA manufacturing) has a much lower minimum PWM and also has throttle curves which smooth out the low end control further. If you are using a RTR style ESC, replacing your ESC is probably a good first choice to get better low speed control.