Understanding ESC PWM and Timing settings

[hillsmaverick]

I hope someone can demystify the motor ratings for me. As I understand it the kv rating in thousand rpm/volt. In other words the same motor would have 2x rpm on a 6 s than a 3s. But I see no power ratings ie HP watts or amps. how do I know what motor to get.

[npomeroy]

Originally Posted by hillsmaverick

I hope someone can demystify the motor ratings for me. As I understand it the kv rating in thousand rpm/volt. In other words the same motor would have 2x rpm on a 6 s than a 3s. But I see no power ratings ie HP watts or amps. how do I know what motor to get.

Motor kv is motor revs per volt, so 6S (23v) on a 1150 kv motor gives 23 x 1150 = 26,450 rpm at 100% power. Take your pinion teeth divided by main gear teeth (e.g. 16/170 (typical for TREx550) = 0.094) to give the reduction in rpm between motor and head speed (26,450 x 0.094 = about 2500 rpm HS).

So find out from the kit instructions or from forums what is a suitable rpm for your model. The other thing is the power rating. See http://media.hyperion.hk/dn/hs/hs-spec.pdf especially page 2 for guidance on motor selection according to model.
Note that Watts = amps x volts.

Note that for scale models the HS can be much less than 3D versions and motor and gearing are often modified accordingly.

[Bob O]

I'm running the Scorpion 2520-1360kv motor on 6S. The calculation gives me a value above 15, but I've been running 8 on pwm all this time. I've never tried 12 or higher. I haven't heard from anyone whose tried a setting higher than 8 pwm on this motor.

My ESC temps are good, about 155*F after a hard flight. Next time out I'm going to increase the pwm and check the log after one flight to see if the temp went up significantly. I'll also log the power, but see if I can "feel" it in flight as well. The motor is powerful as it is, but I just want to see if a higher pwm setting is somehow "better".

[badfrog]

Originally Posted by Bob O

I'm running the Scorpion 2520-1360kv motor on 6S. The calculation gives me a value above 15, but I've been running 8 on pwm all this time. I've never tried 12 or higher. I haven't heard from anyone whose tried a setting higher than 8 pwm on this motor.

My ESC temps are good, about 155*F after a hard flight. Next time out I'm going to increase the pwm and check the log after one flight to see if the temp went up significantly. I'll also log the power, but see if I can "feel" it in flight as well. The motor is powerful as it is, but I just want to see if a higher pwm setting is somehow "better".

I will be interested to hear the results

[AirbusDriver]

I dont really know what these definitions actually mean, the only thing i did was lower the pwm value to 8khz from 12khz and timing to low. Its like night and day now, Esc temp was reduced to 61C from 97C and motor was much more Cooler.

There's no performance lost at least i cant feel.

That values was with T700DFC 2150Rpm headspeed and CC120.

Sent from SpaceShipOne...

[AirbusDriver]

Everything is very smooth and temps are really nice with lower pwm and timing.

My current settings are pwm 8khz and low timing.

Performance is great but it seems That gov is Not holding the headspeed at Stunt 1,which is 2000rpm.

But it is very stable at Stunt 2 which is 2150rpm.

Gov gain is 19and Stunt 1 is 70flat, Stunt 2 100 flat.

Why do you guys think Stunt 1 seems to loose hs in pitch pumps and tictocs,?

Thanks in advance.

Sent from SpaceShipOne...

[emederos]

Originally Posted by npomeroy

Motor kv is motor revs per volt, so 6S (23v) on a 1150 kv motor gives 23 x 1150 = 26,450 rpm at 100% power. Take your pinion teeth divided by main gear teeth (e.g. 16/170 (typical for TREx550) = 0.094) to give the reduction in rpm between motor and head speed (26,450 x 0.094 = about 2500 rpm HS).

So find out from the kit instructions or from forums what is a suitable rpm for your model. The other thing is the power rating. See http://media.hyperion.hk/dn/hs/hs-spec.pdf especially page 2 for guidance on motor selection according to model.
Note that Watts = amps x volts.

Note that for scale models the HS can be much less than 3D versions and motor and gearing are often modified accordingly.

For 6s you don't use the full 25v for this calculation?

[emederos]

Originally Posted by emederos

For 6s you don't use the full 25v for this calculation?

Can you explain what the reduction in motor and headspeed mean? The second calculation

[npomeroy]

Originally Posted by emederos

For 6s you don't use the full 25v for this calculation?

Sure it may be more correct to use 25v, but the voltage fades from about 25 to 22 during a flight so the lower value gives the HS near the end of the flight.

[npomeroy]

Originally Posted by emederos

Can you explain what the reduction in motor and headspeed mean? The second calculation

"Take your pinion teeth divided by main gear teeth (e.g. 16/170 (typical for TREx550) = 0.094) to give the reduction in rpm between motor and head speed (26,450 x 0.094 = about 2500 rpm HS)."

To take simpler numbers: If the motor pinion had 10 teeth, and the main gear had 50 teeth, the motor would rotate 5 times to make the main gear go round once: a 5-to-1 reduction. 10/50 = 0.2.

[emederos]

Originally Posted by npomeroy

"Take your pinion teeth divided by main gear teeth (e.g. 16/170 (typical for TREx550) = 0.094) to give the reduction in rpm between motor and head speed (26,450 x 0.094 = about 2500 rpm HS)."

To take simpler numbers: If the motor pinion had 10 teeth, and the main gear had 50 teeth, the motor would rotate 5 times to make the main gear go round once: a 5-to-1 reduction. 10/50 = 0.2.

Ahhh ok got it ....so i would use that number for actual headspeed not the kv multiplied by voltage

[npomeroy]

Originally Posted by emederos

Ahhh ok got it ....so i would use that number for actual headspeed not the kv multiplied by voltage

Two steps

1. Calculate motor pinion speed by kv x volts

2. Calculate the HS; by motor pinion speed x gear reduction.

[Supertuna]

Reading this thread and would like to ask you guys a question with my new Goblin 500 build with scorpion HKIII 4020 1100kv with CC Edge 100 esc....have motor timing on 5 and 8khz.....poles on 10 as per scorpion website but motor stuttering on start up and will only run for 4 sec before cutting out and esc beeping with high current error....

[KickerOfElves]

In the formula given, kV*poles*voltage/20 (sometimes it's 20k), what does the constant 20 signify? At first I thought it had something to do with getting a switching frequency above the level where most people can hear (20000Hz). Can somebody let me know?

[nabl74]

Not my words. Extracted from another forums response to a similiar question

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Here is the basic nuts and bolts of some ESC setting.

Motor timing
If you advance the timing the motor will put out more power at less efficiency and run hotter. On the other hand if you run the motor with retarded timing the motor will not produce the power it is supposed to. There is a happy balance on what is the right timing for your motor.

PWM Frequency
Another item to consider when setting up an ESC is the motor PWM (Pulse Width Modulation) frequency. The short explanation of PWM is how much power it sends to the motor with each pulse (how long the window is open for). The higher the PWM frequency, the hotter the ESC usually gets. A good way to calculate a starting PWM is to use the following calculation:

KVxVxPoles/20=PWM
Scorpion 4025-550 on 12S example:
550x44.4x10/20=12210

Scorpion recommends an 8 PWM with 5 degrees of motor timing. By the calculation this motor should run well at a 12Khz frequency.

Motor temperature and ESC temperature will always dictate your limits on each. The higher the timing and PWM the more power the motor should make at the cost of efficiency, flight time and increased operating temperatures.

Matching motor KV/pinion gear/headspeed/ESC output

Further consideration needs to be given to motor KV/gearing/desired headspeed. An ESC will run the coolest at 100% output because the FETs are not being asked to switch on and off. The lower the ESC output to the motor, the hotter the ESC will get if you overgear the motor because the FETs are off longer but still have to transfer the same amount of current. Remember the voltage does not change. I will use a simple but unrealistic calculation to show what I mean.

Lets say we have a motor that has a peak of 2000 watts and is set up on 6S with a 100 amp esc
Example 1 - Proper set up, gearing/motor KV matched to desired headspeed, ESC output is 100%
2000w/22.2v=90.1 amps (life is good)
Example 2 - Gearing too high, ESC output to get desired headspeed is 50%.

2000w/22.2v/.5 (50% output)=180 amps.
So you wind up with a large increase in current trying to be transferred to the motor with each pulse of the ESC caused by the shortened switching time of the FETs. This will cause extreme heat in the ESC and lead to release of the magic smoke.

These are the ultra simple explanations of each, if you want to find out more details google them.

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