Motor - Balance Data

[RichWest]

I believe I have a motor that is out of balance by a large margin. However after recording with my phone's accelerometer and a vibration app I'm not sure how to analyze the information correctly.

The motor testing was done one at a time through Mission Planner. The phone was placed on the battery laying flat on its back, with the top of the phone pointed to the front of the Solo.

Settings in MP - 50% Throttle for 2 seconds
App's Data sample rate was at 10ms intervals
I've charted 350 data points for each of the 4 motors, shown below.

I understand the magnitude of vibration is what I'm looking to solve. I'm not sure I set the test up correctly, but with everything the same it does offer some comparison data to work from. Is the relevant data the X, Y or Z when balancing a motor?

And then the other question is the frequency. The charted data shows different frequency for the vibration recorded. For example Motor 1's vibration frequency was short, whereas Motor 4's frequency was long. How does that figure into whether a motor is unbalanced or not?

Motor 4 is my questionable motor. Having recorded the data, it appears that 2 & 4 are similar.

 

[Maddog]

Wow- it's all Greek to me! There is a YouTube video that uses that same app or a similar one- is that what you are using?
The guy in the video explains what settings to select but I can't remember if he said to use X, Y, or Z.

 

[RichWest]

He stated Zed or the Z axis...from the video I watched at least. Then he said he wasn't sure why, but it worked for him. Another learning curve I guess...

It's interesting how motor magnets are set and then tested in mass production.

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[Maddog]

I always thought it made more sense to remove material to balance instead of globbing on glue, tape, etc.

I was concerned about removing material from a prop hub to balance the hub. Didn't want to compromise the strength. Anybody have comments about that?

 

[RichWest]

I always thought it made more sense to remove material to balance instead of globbing on glue, tape, etc.

I was concerned about removing material from a prop hub to balance the hub. Didn't want to compromise the strength. Anybody have comments about that?

I think removal is the best regarding the motors, if you had a precision machine for doing the removal. Otherwise it seems close enough by adding material or at least the most forgiving. Besides, most everyone already has the supplies required. Tape seems temporary though.

Around the prop hub I'd prefer to add material rather than remove. Like you said structural concerns.

Understanding how the magnets are installed, since they are the portion that spin, I can imagine the epoxy is the offender for the balance. I believe balancing the motor provides the best vibration reduction. Balancing propellers is more than just weight and then once combined with a motor other variables play further on balance. In the end this isn't precision equipment, just hobby grade. We make it precision-like by the effort to improve.

 

[Toiletbowl]

im comfident with this product T-MOTOR specialized in motors and props.

 

[RichWest]

im comfident with this product T-MOTOR specialized in motors and props.

Got any that will install directly on the Solo?

 

[Toiletbowl]

Got any that will install directly on the Solo?

as i chat with the sales on skype they have now props for solo not sure about the motor, i have anti gravity self tightening props before in my phantom very sharp and stable. lemme talk again the sales agent wait

 

[Maddog]

I think removal is the best regarding the motors, if you had a precision machine for doing the removal. Otherwise it seems close enough by adding material or at least the most forgiving. Besides, most everyone already has the supplies required. Tape seems temporary though.

Around the prop hub I'd prefer to add material rather than remove. Like you said structural concerns.

Understanding how the magnets are installed, since they are the portion that spin, I can imagine the epoxy is the offender for the balance. I believe balancing the motor provides the best vibration reduction. Balancing propellers is more than just weight and then once combined with a motor other variables play further on balance. In the end this isn't precision equipment, just hobby grade. We make it precision-like by the effort to improve.

Yep, I agree.

 

[Guy Canavaggio]

I noticed the same vibration today , it is a slow resonating hum with peaks as the gimbal vibrates pendulum like in a hover flight no wind. The props are balanced vertical and horizontally . The only thing left to check is the motors. Will try to take a video .

 

[RichWest]

...The only thing left to check is the motors. Will try to take a video .

The other possibility is that the vibration is being picked up by the thick control wire , and hdmi rigid cable ...

Another thread topic on the HDMI cable, so let's not bring that into the motor balancing thread. But I do agree it is an issue if not properly routed.

 

[RichWest]

I ran four further tests last night on motor 4, moving the tape around the circumference and then recording the results. This is a time consuming process just to acquire the data. Then a certain amount of time to format the data into a graph....to visually compare results.

I ended up using the Z value and comparing the average peak high and low value of approximately 150 data points. I filtered out the start and stop motor readings, just used the run measurements. I then subtracted the low from the high average readings and then determined the results. The improvement were minimal for the second round, but I was able to identify the quadrant that needed added weight.

Rather than continue testing, I had the brilliant idea to disassemble the #4 motor pod. Curiosity got the best of me, since the test results didn't match what I believed was the issue. I wanted to see how the motor bell housing was assembled and the method for balancing from the factory. The first video above showed that the process is all done by hand. It appears that epoxy is placed into the housing initially and then that material is removed by hand to further balance. I would imagine this is done three to four times per a motor to obtain an acceptable balance. Again these are hobby grade motors... I could only imagine what a NASA funded motor would cost.

I was able to reassemble the motor pod close to factory, hot air solder wand made easy the plastic tabs retaining the circuit board both off and on. The shaft's C-clip is not spring steel, as it easily deformed when removed. I took several photos and measured the thrust washer and c-clip. Will post that information later. Didn't mess with removing the bearings, since someone else is already replacing those in another thread....and mine aren't having issues.

Since the motor was disassembled, I will start my testing over from the beginning. I would like to have all the motors balanced to a higher level. Based on first tests however, I think default balance is acceptable.

This is not a Solo exclusive effort. At this point this is just an exercise in how the motors are assembled and the effects of that assembly. I imagine, at this point, there are several things contributing to vibration. The different frequency of the four motors alone have an intersecting point some where within the craft where they converge. I'll leave that research to someone with a better pedigree and is better equipped....

Again my interpretation on the subject is not based on being an expert. I'm just a mechanic. Nothing ventured, nothing gained.

 

[Deleted member 2044]

Maybe I'm being captain obvious on this, but could these vibrations be caused from aerodynamic root reasons rather than a mechanical root reason? As stated above these are just hobby grade motors. Their frequencies are most likely not going to match each other. If you're having significant problems with the quad, I would test the quad in different environments, flying outside vs. flying inside (a large area like an indoor basketball court and in a manual mode like Stabilize, of course) and see if that affects how your quad is performing.

Often people think air is a solid current that can change velocity but it's more complex than that. There are eddies and pockets of air with different temperatures. This uneven air is simply known as turbulence. The quad is subject to turbulence just as much as an airplane or helicopter. But every aircraft has it own unique characteristics for when it encounters turbulence. When an airplane encounters turbulence it's often felt as bumps, and sometimes the turbulence can slightly change the pitch and roll of the airplane. In helicopters, turbulence is seen as a yaw motion.

Since a quad is closely associated with helicopters aerodynamics, when a quad experiences turbulence it can be seen as abrupt yawing. But due to the onboard computers and compass, the quad is going to adjust to maintain a directional heading. This change in motor RPMs with different motors having various RPM settings can cause vibrations. It's something that can be felt and heard. In a multi engine propeller airplane, when the two engines are not matched at the same RPM, a humming is heard and a vibration is felt. Likewise, a quad is subject to this phenomena also.

Another aerodynamic factor could be one propeller produces lift more efficiently than another. Because our props are fixed pitch props, lift coresponds directly with the motor RPM. Increase RPM, increase lift, and vise versa. If one prop produces lift more efficiently than another, the motors RPMs will vary if in level flight. This is due to the onboard computer attempting to keep the quad level, rather than regulating all the motors to a constant RPM. You can see this by slightly pulling on one of the quads legs and subsequently that motor will increase in RPMs to bring the quad back to level flight.

In a nutshell, when the motors RPMs don't match, a vibration is caused. The size of the vibration will also depend on how far apart the motors RPMs mismatch. Assuming your motors don't have a major mechanical problem in which case it should be replaced, try different flying environments (outdoor vs. an appropriate indoor location flying in a manual mode) to see if the vibrations change and then also try different props. It would be a bummer to rip apart a motor to find out that it's not a major mechanical problem. Best of luck in your testing. I'm curious what you discover.

 

[Maddog]

Ummm- were flying quads, not the space shuttle..

 

[Deleted member 2044]

Ummm- were flying quads, not the space shuttle..

My apologies. That was quite the Miley Cyrus - Wrecking Ball entrance to the thread. I just would hate to see the guy go thru all this testing to find out it's something not in our control.

 

[RichWest]

Maybe I'm being captain obvious on this, but could these vibrations be caused from aerodynamic root reasons rather than a mechanical root reason? As stated above these are just hobby grade motors.
<snip>
In a nutshell, when the motors RPMs don't match, a vibration is caused. The size of the vibration will also depend on how far apart the motors RPMs mismatch. Assuming your motors don't have a major mechanical problem in which case it should be replaced, try different flying environments (outdoor vs. an appropriate indoor location flying in a manual mode) to see if the vibrations change and then also try different props. It would be a bummer to rip apart a motor to find out that it's not a major mechanical problem. Best of luck in your testing. I'm curious what you discover.

Interesting, thank you for sharing. You make valid points through out and I will agree most if not all. Just not at that place just yet.

From my perspective you can't rule out the aerodynamic root until you've ruled out the mechanical side first. It is what the manufacture or I am able to control or improve upon. Like you said the real world usage plays hard on identifying vibration. Add in the logic to compensate for these dynamics, its amazing we can even get a still picture let alone a video of any quality.

I should have prefaced as to how weird I am about these things. I did my own study on how clay targets break with the "golden pellet". Never published, as no one was really interested as to why a clay target broke apart when hit by one pellet and other times not. Bob Brister was interested, he wrote the book on shotgunning. Answer, it's the imbalance that causes the target to break apart. Moment of inertia and those forces on the fragile target, rpm is the key. So I learned to have a higher break percentage is by taking the bird as soon as I could out of the machine. Slower spin rate at the end of flight and I was unlikely to be as lucky with one or three pellets. My test rig was a drill press, high speed video camera, bb gun and a really interesting rig to hold clay targets while spinning. It was 6 weeks of studying, set up, destroying targets and cleaning up... Really interesting and never spent more than $5 for the results.

So am I wasting my time, maybe but who cares. I appreciate you taking the time to add to the conversation. Never was offended, I liked Miley Cyrus when she was a younger singer....but now not so much.

 

[Maddog]

My apologies. That was quite the Miley Cyrus - Wrecking Ball entrance to the thread. I just would hate to see the guy go thru all this testing to find out it's something not in our control.

No worries! At least you had something pertinent to add to the thread..

 

[Raybro]

Ummm- were flying quads, not the space shuttle..

I'll just fly.....

 

[Maddog]

I'll just fly.....

Ditto- I don't know what the engineers are talking about.

 

[Deleted member 2044]

Interesting, thank you for sharing. You make valid points through out and I will agree most if not all. Just not at that place just yet.

From my perspective you can't rule out the aerodynamic root until you've ruled out the mechanical side first. It is what the manufacture or I am able to control or improve upon. Like you said the real world usage plays hard on identifying vibration. Add in the logic to compensate for these dynamics, its amazing we can even get a still picture let alone a video of any quality.

I should have prefaced as to how weird I am about these things. I did my own study on how clay targets break with the "golden pellet". Never published, as no one was really interested as to why a clay target broke apart when hit by one pellet and other times not. Bob Brister was interested, he wrote the book on shotgunning. Answer, it's the imbalance that causes the target to break apart. Moment of inertia and those forces on the fragile target, rpm is the key. So I learned to have a higher break percentage is by taking the bird as soon as I could out of the machine. Slower spin rate at the end of flight and I was unlikely to be as lucky with one or three pellets. My test rig was a drill press, high speed video camera, bb gun and a really interesting rig to hold clay targets while spinning. It was 6 weeks of studying, set up, destroying targets and cleaning up... Really interesting and never spent more than $5 for the results.

So am I wasting my time, maybe but who cares. I appreciate you taking the time to add to the conversation. Never was offended, I liked Miley Cyrus when she was a younger singer....but now not so much.

Thats a really interesting point about clay pigeons. I'm gonna have to binge watch the show Top Shot now and look for that! Anyways, back to the original thread topic, let us know what you find from your testing. I'm really curious on that.