MOT_THST_EXPO setting for T-Motor Flame ESCs

ArduCopter Copter 3.5
1

Hi,

finished my latest build and about to start tuning.

I am using T-Motor Flame ESCs + T-Motor FA24 x 7.9 Props + T-Motor MN701S 135KV motors (all @ 12s).

I read here in another thread that T-Motor ESCs apply thrust linearisation and thus the default MOT_THST_EXPO setting of 0.65 is probably not ideal for this setup.

I have not been able to setup my thrust measuring stand / dynamometer yet and calculate the right value - there’s just not enough time for everything it seems :frowning:

Has anyone determined EXPO values for T-Motor ESC+Motor+Prop combinations by any chance?

Thanks a ton,
Christian

1 Like
2

Isn’t the expo heavily dependent on prop design?

3

if so, it’s because we graph static thrust, not propellers optimal speed… most of the non-linear response is caused by ESC code/electronics if not compensated.

I just started to work on my good old thrust/current/power/voltage sensing/plotting rig to add RPM , so I’ll soon know if power curve / thrust curve / rpm curve are significantly different, and how much a change of propeller changed it…

4

Hi,

I completed the measurements on the thrust stand yesterday and my results are as following:

Motor: T-Motor MN701s (135kv)
Props: T-Motor FA24x7.9 (Folding CF Props)
ESC: T-Motor Flame 60 HV
Power: 12s

MOT_THR_ARM 0.08
MOT_THR_MIN 0.11
MOT_THR_MAX 0.95

MOT_THST_EXPO 0.18

I have not had a chance to fly with this EXPO value yet - will provide an update once done.

Thought I’d post her in case anybody had the same config by any chance…

Christian

5

Interested to see how it flies with .18. Would love to see video flying around.

6

Your data is appreciated, thanks for sharing. Expo of 0.18 sounds about right - I’ve heard 0.2 to 0.3 is common for T-Motor and KDE ESC’s.

Oh and just a note: the throttle expo is meant to be measured ONLY for the PWM range used in flight, ie between MOT_SPIN_MIN and MOT_SPIN_MAX. If you include the bottom and top ends that aren’t experienced in flight, the expo will be off. Just wanted to make sure you were aware of this.

On a side note, does anyone know if DJI ESC’s also linearize throttle?

7

We had a similar setup. We used MOT_THST_EXPO 0 which seems good enough. We did not have a thrust setup so I do not have a curve for Flame 60A. Just assumed it was linear.

8

Hello my bro ,
I have the same Motor 、Props and ESC with a quad , and
got some problem when auto flying . The props sometimes stop spin . maybe 1second or 2 ,looks dangerous

default setting . expo 0.65 weight 9kg

so I change the expo to 0.18 would be solve the problem?
thanks

9

You haven’t by any chance tested any Alpha ESCs?

10

Alpha ESCs are much better than Flame. I use Alpha on a good amount of my builds.

11

What thrust expo do you use for those?

12

0.2 has worked well for me - but it depends on a lot of factors. I use the integrated propulsion series which seems to have different expos than the stand-alone ESCs. Its a mess from T-Motor’s handling of ESC firmware and whatnot, so you kinda just have to test a couple to converge on a solid value.

13

I run the 605-S arm set on 6s lipo. I tested 0.2 and 0.4. Didn’t notice any difference. I also tested 0.76 (calculated value from wiki) which did not work as well and introduced some over all instability.

I also noticed there’s two different firmware’s for this motor/esc combo using the data link. Have you encountered this?

14

Yeah the firmware changes all the time based on when you ordered the sets. I have used the MN501S (normal and coaxial) and MN6007 packs and they all seem to work pretty well in that 0.2 to 0.4 range you specified. I always start with 0.2 and if I feel instability then I start tweaking it higher towards 0.4.

1 Like