CD-rom motor-test-stand

[Hans]

hey

I just made this teststand and thought you should see it.
The 2 multimeters are build together, the esc is connected to a homebuild servotester and as you can see the motor is put on a letterweight. I test all motors as a "pusher".
I just connect the accu I want to use in the setup, to the meter on the right, turn the button on the "nice blue" box ;) , and now I can see Amps, Volt and thrust. My plan is to put a rpm-meter on it too.


What do you think, smart isn´t it. :)

[helifrek]

I like it, nice and simple. :) good job, can't wait to see it with the tach/rpm meter.

Brandon

[ki0qm]

How is the motor mount connected to the scale?

[Hans]

I simply used some very strong dubblesided tape I had ( I don`t know if it is called that, but you know the kind of tape with glue on both sides), but you could use any kind of glue or epoxy.

sorry if my english is a "little danish", but there is a reesson :p

here are some closeups:

[The Tellurian]

I would get a large piece of plexi glass or lexan prefered to use as a shield just in case your closely looking at the readout and the motor throws a blade. :(

Richard [ask me how I know :o ]

[burro breath]

i would go woth lexan from my bad experience plexiglass will shadder.(thrown blade@ 87,000rpm) :)

[latrans]

i would go woth lexan from my bad experience plexiglass will shadder.(thrown blade@ 87,000rpm) :)


What 'blade' did you have spinning at 87,000rpm and what motor was spinning it?

Latrans

[Hans]

Hi I´m back

I have now put a tachmeter on my test-stand. It gave me some problems but now it works.
I took the "eye" out of the tachmeter and placed, pointing down,it in the white plaststand you can see on the picture. Then I placed a small diodelight on the scale, pointing up, now it works great.

Now I can see A, V, rpm and thrust at the same time, what more do you need ;) :D

What do you think of it? don´t you think it is a little smart :)

[ecologito]

Man, that looks great :)

That is something that I need to build

[fly_boy99]

Hans

Now all you have to figure out is how to measure noload rpm!!!

:eek:
fb

[Hans]

Now all you have to figure out is how to measure noload rpm!!!

You had to say that, didn´t you? X%#" :censored: , now I just thought I was finish with it, and I was very happy with it. Is there anything else you want me to put on it, now that I have to start all over again. ;) :D :p :D

[ecologito]

:rolleyes: :rolleyes: You could put a microwave next to it so you can have fresh popcorn while testing how long will the motor fly full throttle on a fresh pack of batteries :D :D :D :D

[Hans]

Lol :) :D :D :D

[jj1]

Hans

Now all you have to figure out is how to measure noload rpm!!!

:eek:
fb

Noload can be measured without any prop:

-JJ

[olmod]

Noload can be measured without any prop:

-JJ
Will it read true rpm's with any number of stator /poles ?

[fly_boy99]

Uh that's why I said noload.... :p


Noload can be measured without any prop:

-JJ

[qv_]

Will it read true rpm's with any number of stator /poles ?

on a CDR (stator 9 / poles 12) it work like a 6 blade propp on WOT
it don't work between zero - 1/2 throtel

/jan

[wjbite]

Hey JJ1- Looking at that drawing leads me to believe that your no load measuring rig is a much better way to measure RPM all the time, load or no load.
No reason to have that light source and sensor hanging around the prop, is there? Just use an LED and resistor. Cleans up the test stand.
Also, if you are into electronics, then do away with the tach that needs an LED for the light source - and use any other circuit you happen to have around that will count pulses across two of the motor phases.
In either case just count the pulses you have with the stuff you have on hand and do the division to get RPM.
Of course, this all assumes that you are working with brushless.

[wevets]

Doesn't the method in message #14 assume that the ESC will adapt to the motor and that it will drive different motors with different KVAs differently? I'm probalby speaking from ignorance on this, but I always thouht that a given ESC would drive all motors the same for a given servo input, and that the motor would follow the "rotating magnetic field" created by the ESC drive to the motor as best it could. For this method to work, the ESC has to adapt to what its seeing from the motor on its drive leads.

Can someone educate me here?

Thanks.

wevets

[wjbite]

I could be wrong here, but, my understanding is that CDR motors rotate in FULL synchrous with the rotating field - NO slippage, like there is in some other types of motors. So, If that is true, you can detect the RPM of the rotating field with JJ1's circuit. The only correction that needs to be made is for the number of field rotations that is required to cause the motor to rotate once. And that is related to the number of magnets and field poles. There should be no change in that multiplier constant under changing loads. Just like number of blades passing the light detector per revolution - using a light path broken by prop blades changes the multiplyer as the number of blades is changed.
Uh ... I hope I made my thoughts clear.... not sure.
Anybody know if I have good info about no slippage?

[PlaneCrazee]

Doesn't the method in message #14 assume that the ESC will adapt to the motor and that it will drive different motors with different KVAs differently? I'm probalby speaking from ignorance on this, but I always thouht that a given ESC would drive all motors the same for a given servo input, and that the motor would follow the "rotating magnetic field" created by the ESC drive to the motor as best it could. For this method to work, the ESC has to adapt to what its seeing from the motor on its drive leads.

Can someone educate me here?

Thanks.

wevets
The sensorless esc drives the phases and then tests the back emf to tell where it is. The input signal from the reciever limits the duty cyle the esc will produce at the pwm frequency(much higher than the servo fram rate) This is "seen" by the motor as a difference in the voltage available hense the differnce inn the rpm. It does not care how many poles or Kv the motor is. The more pole the fewer rpms the motor will get per commutation. A motor with a more poles usually has a lower Kv for this reason.

Hope that makes more sense of it.

[PlaneCrazee]

Noload can be measured without any prop:

-JJ
Very cool idea... very cleaver. I need to add that to my test stand.
you could do it the boring old 2 lines drawn with a black sharpie if you want to be low tech and skip the math.

[wjbite]

JJ1: have you tried that circuit?
I forgot about the much higher freq. signal (the PWM) riding on that waveform mentioned by PlaneCrazee.
If your circuit works then your RPM meter must be incapable of responding to the higher frequency and is, in effect, filtering it out.
If you haven't tried it you might have to include a low pass filter with the LED so that the LED doesn't respond to the PWM and blink too often. You might be able to get away with a passive filter made up of just resistors and capacitors.

[jj1]

Hi,
yes have tried that out. Got the idea originally from 'cp1' in the drive calculator thread.
Tested only with 9tooth 12 pole motor.

Repeating myself:
"That led trick was great, inserted 1k resistor and ordinary led in between 2 phases and those 'led-rpm' readings are divided by 3. Tach was set to '2-blade prop'.
Led reading 38,7krpm => 12,9krpm"

Verified readings to be accurate enough with a tiny 'prop' made out from a strip from business card...
Havent tried this method with 'loaded' motors, only noload.

-JJ

[qv_]

Hey JJ1- Looking at that drawing leads me to believe that your no load measuring rig is a much better way to measure RPM all the time, load or no load.
No reason to have that light source and sensor hanging around the prop, is there? Just use an LED and resistor. Cleans up the test stand.
Also, if you are into electronics, then do away with the tach that needs an LED for the light source - and use any other circuit you happen to have around that will count pulses across two of the motor phases.
In either case just count the pulses you have with the stuff you have on hand and do the division to get RPM.
Of course, this all assumes that you are working with brushless.

I only use it to get Io. It gives 0.1A less (on mini APEX) compere to a thin plastic disc from a HP DeskJet.

The LED is not stable on low RPM
If RPM is 1000 then LED show 25000

LED works greate on WOT


/jan

[wjbite]

As Arti Johnson from Laugh In used to say:
velly in teh lesting.

All of this info
from PlaneCrazee, JJ1, and qv
seems to be consistant with a need to have a filter to get rid of the PWM pulses.
It works at full load because the PWM pulse width is about 100%. Which means that the unwanted pulses are very sharp (very high freq components) and the circuit is not able to respond to that, so all is well in foamie town.
But at lower speeds the system is able to respond to the PWM pulses, therefore counting unwanted pulses and driving the RPM reading way up.

Guess I will have to put this on my looonnnngggg to do list :)

[jj1]

Update on this noload measurement setup.
It doesent work with delta windings...
or atleast the results are not dividable with 2 or 3

-JJ

[frankyfly]

jj1 any update on the project.

I built it ( link (http://www.rcgroups.com/forums/showthread.php?t=878913) ) as per plan, but I didn't get reasonable results.

How we can improve it, it seems could be a smart tool ?

We need some electronic expertise to chime in.

Franky

[lucent]

How are you making your amp measurement. Are you running it straight trough the ammeter setup on the multimeter or are you measuring the voltage drop across a know resistance?

[frankyfly]

Lucent what are you referring to ?

I resurrect this old thread hoping somebody could help me solve the problem using the flashing LED to mesure prop RPM indoor.

For the amp measurement I'm using the EMETER tool. The value is just there on the display. Its probe is between the battery and the ESC.

Franky

[jj1]

jj1 any update on the project.

I built it ( link (http://www.rcgroups.com/forums/showthread.php?t=878913) ) as per plan, but I didn't get reasonable results.

How we can improve it, it seems could be a smart tool ?

We need some electronic expertise to chime in.

Franky

Sorry Franky but i dont expect this setup to work reliably on prop loaded motors.

If seems to work on noload and WOT and 9N12P WYE. :rolleyes:
Change any of those four parameters and result is unsure. :(

-JJ

[frankyfly]

JJ1 what 9N12P & WYE acronyms stand for ?

Franky

[frankyfly]

Oh gosh !!!

I got it.

You are referring to the statorpole and star configuration. :o

The penny didn't click into the brain. :(

Franky