HobbyGuy10

Hello,


I have been having trouble getting a 3-phase brushless DC motor (connected to a controller via an ESC) to reach its max RPM, I only get around 50% of the RPM I should be getting. I don't really want to get into the specifics.


To troubleshoot, I would like to measure the voltage coming out of the ESC with a multimeter. Is this possible? How would I hook up my lines to ensure that I do not short the ESC or the multimeter? My thought is, if I am feeding the ESC 24V and I send a PWM signal of 80%, the ESC should read 24*0.8= 19.2V. Is this a reasonable plan?


I have already tried different combos of motor and ESC and the results are always the same. I also looked at the PWM signal I am sending and it looks fine.


Thanks!

solentlife

No you cannot measure like that as the motor is in effect a 3 phase AC unit.

It sounds like you may have timing out on the ESC ....

OK - info please :

What LiPo / Power supply are you using ?

What is the ESC amp rating and for how many cells ?

What motor are you using with what KV rating ?

What are design specs of the Motor ?

What prop are you using on it ?

Once we know that - then we can hazard a guess ..

You can also use eCalc online to see what sort of results the motor should give.

quorneng

The voltage out of the ESC will not effect the rpm of a brushless motor, only the power it can produce. The rpm of the motor is controlled by the frequency of the ESC's pulses, the number of armature poles and the number of magnets.

HobbyGuy10

Thank you for your responses. So after narrowing it down further, it is most likely the ESC not being correctly calibrated.

I have the following ESC https://hobbyking.com/en_us/ztw-spid...-firmware.html. But there does not seem to be a very thorough guide on how to re-calibrate the ESC. The 3 steps they have in their manual did not work.

Any suggestions for re-calibration?

ron_van_sommeren

A brushless controller + motor constitute an isosynchronous closed loop system. Therefore, without a working motor connected to the ESC, you won't be able to see/measure anything.
A brushless motor is not very different from a brushed motor, it is a brushed motor with electronic commutation, the controller, instead of mechanical commutator and brushes.
Same motormodel, same three motor characteristics (velocity konstant Kv, no load current Io and motor resistance Rm). Same calculations for current and power drawn.

Safety
Remove prop when setting up or changing power system.

The three motor/ESC wires are equivalent, but not identical. They carry the same power signal albeit with a 120degree phase ('time') difference, switching between zero and full voltage. One complete voltage cycle corresponds with one magnet passing a stator pole.

You can connect the three motorwires anyway you want. If motor runs in the wrong direction, just swap any two of the three motorwires. But NEVER EVER swap battery wires to reverse rotation, reversing battery polarity will ruin you controller, bigly, in the blink of an eye
Different colours for motorwires are handy for remembering the ESC→ motor connections, that's all

See also these
brushless motor animations and simulations - RCG


Motorvoltages at full throttle, no chopping up voltage in pieces.



Motorvoltages at partial throttle, PWM chopping ('grass') to reduce effective voltage.



Zoomed in on above scope trace directly above.
V is chopped voltage, I is smoothed current.

from www.consult-g2.com → course


Scope traces from www.aerodesign.de/peter, DIY brushless motor building (english&german)

quorneng

Just as an aside how do you know what rpm the motor is supposed to achieve? How have you measured the rpm that you are achieving?
The fact you have tried other combinations with no improvement would suggest your rpm expectations are incorrect.
Are you using the full travel of the throttle stick and not starting from the centre?

The calibration method given is 'bog' standard. Set throttle to max turn on the radio, power up the ESC, two beeps immediately set throttle to zero. two beeps, disconnect ESC from battery.
If this does not work then something else is wrong.
To get much further you would have to be much more specific on exactly what you have and what you are trying to do with it.

ron_van_sommeren

Connect ESC to other receiver channel, to keep power, and connect servo to throttle channel.
Is servo throw what you would expect?
Can you see output of that channel on transmitter display?
Are mixers, curves, reductions active on that channel?

Use a fresh/new/cleared/reset model memory.

TallyFeli

Hi....Is it accurate to say that you are verifying the battery voltage load or when the engine is running full burden? It tends to be the battery has high interior obstruction and the voltage drops under load, the above meter will show that.
Is your engine a similar kv rating as your associate? Kv is the rpm per volt, and possibly your arrangements are unique.