Different motor rpm

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CaptainAwesome
Posts: 6
Joined: Tue Dec 24, 2013 4:11 pm

Different motor rpm

Post by CaptainAwesome »

Hello! Im just about getting my first quad in the air but before im putting props on it I have a small ( or big ) problem to solve.
When I arm the motors in the GUI the motors are idling somewhere about at 1050 rpm and when I start to give some throttle the motors rpm will vary 50-100 rpm.
I have calibrated the esc:s by activating ESC_CALIB_CANNOT_FLY correctly and the transmitter looks to function properly, the sticks travel from 1000 to 2000 and the middlepoints are at 1500. So is this bad or should I just put my quad on testing-stand?

waltr
Posts: 733
Joined: Wed Jan 22, 2014 3:21 pm
Location: Near Philadelphia, Pennsyvania, USA

Re: Different motor rpm

Post by waltr »

Go fly it or put it on the test stand with props on (be careful) since this is normal when the copter is not in the air.
Remember that the MW FC is trying to adjust the motors speed from what it reads from the sensors.

CaptainAwesome
Posts: 6
Joined: Tue Dec 24, 2013 4:11 pm

Re: Different motor rpm

Post by CaptainAwesome »

Ok, so it tried to fly the quad but with no success. When I gave minimum throttle the quad just flipped over. How much does the frame balancing effect on the takeoff? Anyway heres a printscreen from GUI, the front_L and front_R motors have 160 rpm aberration on the ground with full throttle and im quite confused why.
Attachments
ongelma.png

scrat
Posts: 925
Joined: Mon Oct 15, 2012 9:47 am
Location: Slovenia

Re: Different motor rpm

Post by scrat »

Do not fly in angle mode but in plain acro instead. Set Tx sticks travel from 1005 to 1995. Then calibrate all esc's. But if quad flipped over then check motor so they turn in right direction, maybe props are wrong...or esc's are connected wrong on the fc.

waltr
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Joined: Wed Jan 22, 2014 3:21 pm
Location: Near Philadelphia, Pennsyvania, USA

Re: Different motor rpm

Post by waltr »

Check everything scat mentioned.

the front_L and front_R motors have 160 rpm aberration on the ground with full throttle

These values are NOT RPMs. They are the pulse width in us (micro-seconds) of the commands sent to the ESCs. Do a web search on RC servo PWM to learn about this.

CaptainAwesome
Posts: 6
Joined: Tue Dec 24, 2013 4:11 pm

Re: Different motor rpm

Post by CaptainAwesome »

I tried to set the sticks to travel from 1005-1995 but I somehow didnt manage to change the pitch values so I propably have to let it be 1000-2000. :/ I checked that the motors were in their respective locations (ESC:s connected to right pins 9,10,5 and 6), spinning directions which were ok too and the propellers which were also ok. I did calibrate the esc:s again with ESC_CALIB_CANNOT_FLY and there seemed to be some change to previous but the motors still get too different commands while the GUI shows flat line to all sensors. I have hobbykings Red Brick 20A esc:s which have quite limited programmability so could this be that the calibrating will fail because of it? Oh, and sorry about the rpm confusion, I know that the bars in the GUI show the commands that come from the fc but I still got them mixed. :D

CaptainAwesome
Posts: 6
Joined: Tue Dec 24, 2013 4:11 pm

Re: Different motor rpm

Post by CaptainAwesome »

So I did get my quad in the air after all tough there was little oscillation! The problem was that I didnt calibrate sensors properly before flight and didnt give enough throttle in the takeoff. Now I just have to set PID-values correct and learn to fly the thing. :D

waltr
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Joined: Wed Jan 22, 2014 3:21 pm
Location: Near Philadelphia, Pennsyvania, USA

Re: Different motor rpm

Post by waltr »

Ok, now keep flying.

upilloni
Posts: 4
Joined: Tue Aug 12, 2014 1:34 pm

Re: Different motor rpm

Post by upilloni »

MOTORI.JPG
I have the same problem, but difference is very high...
in the moment I start motors by arming (just with aux1 on my rc turnigy 9x, I cannot find something else) pulses are all 4 motors at maximum value, after 1 sec motors left rear and right front starts to decrease values. I didn't start to fly yet, cause I'm scaring about a bad crash.
Please help me
Thanks

Pilloni

waltr
Posts: 733
Joined: Wed Jan 22, 2014 3:21 pm
Location: Near Philadelphia, Pennsyvania, USA

Re: Different motor rpm

Post by waltr »

upilloni wrote:
MOTORI.JPG
I have the same problem, but difference is very high...
in the moment I start motors by arming (just with aux1 on my rc turnigy 9x, I cannot find something else) pulses are all 4 motors at maximum value, after 1 sec motors left rear and right front starts to decrease values. I didn't start to fly yet, cause I'm scaring about a bad crash.
Please help me
Thanks

Pilloni


This is exactly what the TX is telling the MW FC to do which is YAW.
Look at the Yaw value from the TX/RX and fix this.

Also, if the copter is Not in the Air then the FC can not properly adjust the motor speeds.

If you read through the thread here you would have seen this exact issue asked and answered many times.

upilloni
Posts: 4
Joined: Tue Aug 12, 2014 1:34 pm

Re: Different motor rpm

Post by upilloni »

I'll watch inside for trying to resolve,
thank you.

upilloni
Posts: 4
Joined: Tue Aug 12, 2014 1:34 pm

Re: Different motor rpm

Post by upilloni »

Hi,
now I tried to resolve problem with rc fine adjustements of 2 sticks by moving yaw button. Ok now it's most stable but quadcopter doesn't fly, when I pump throttle automatically motors decrease rpm and copter is stable, but near the ground :cry:
I tried also to hack PID parameters using Multiwiigui Rel 2.2 but I'm too ignorant and failed every test.
I know it's warm and people goes to the beach, but I'm still here with my rc in hands... please, let me appreciate life again :roll:

Thanks
Ugo

upilloni
Posts: 4
Joined: Tue Aug 12, 2014 1:34 pm

Re: Different motor rpm

Post by upilloni »

OK finally I fixed my problem,
I just try to balancing props by using a light tape and a bit patience first using 10*4,5 props and then changing props and using my first choice 9*4,5.
After balancing I start flying easy and funny.
As a prove I detach props from motors with multiwii config connected and I see that pumping throttle without props, motors didn't decrease so I understood that the problem was propellers vibrations.
I think that vibrations may cause any reaction to the sensor and Arduino correct or try to correct decreasing rpm.
Hope can help someone else who find this problem..

Ugo.

waltr
Posts: 733
Joined: Wed Jan 22, 2014 3:21 pm
Location: Near Philadelphia, Pennsyvania, USA

Re: Different motor rpm

Post by waltr »

Yes, vibrations can cause all sorts of bad things. Good you figured it out.

chins
Posts: 1
Joined: Wed Jan 27, 2016 6:50 am

Re: Different motor rpm

Post by chins »

Is it possible to re-stabilize the quadcopter by changing the rpm via code? That is by programming the quad for stability?
Im using CRIUS SE V2.5

wastevenson
Posts: 33
Joined: Thu Jan 07, 2016 5:33 am

Re: Different motor rpm

Post by wastevenson »

Just reading about these vibrations and about how to cancel unbalanced motor "bells" with a vibration sensor and had a thought. Has anyone ever had the idea to use a vibration sensor on the flight controller to cancel out any vibrations the acc / gyro may be sensing?

Kbev5709
Posts: 451
Joined: Mon Aug 17, 2015 5:56 pm

Re: Different motor rpm

Post by Kbev5709 »

wastevenson wrote:Just reading about these vibrations and about how to cancel unbalanced motor "bells" with a vibration sensor and had a thought. Has anyone ever had the idea to use a vibration sensor on the flight controller to cancel out any vibrations the acc / gyro may be sensing?

If you aren't using a prop balancer at least as good as this Dubro, then your props are not as balanced as you think.
Image
Step 1. Start by using a phone app to sense the vibration of the motor bell with no props on and use tape to fix any imbalance. Step 2. Then use a balanced balancer like the Dubro to get your props done right.
Then for the FC the right approach is to first balance your bells and props, then use some old hard drive shock balls or gimbal balls and let it (the FC) float between the (stainless) bolt head and the shock ball using nylon standoffs to hold the balls and bolts. If you do it right in the bells and props department this will be more than enough vibration resistance for excellent performance. If you need to resort to using a vibration sensor on the FC to see how bad the vibrations are there then repeat steps 1 and 2. See Photo.
Image

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