Quad motors get hot

[Cyberdactyl]

If your motors are out of alignment where you can't visually see, that isn't the problem. Same with the CG being off a couple inches on a quad your size. But I'm sure you discovered that.

Now it's time to look at more exotic possibilities.

One is the way your board is mounted. I suggest this because I had a very peculiar problem with my tri. I had the KK2 resting on the trimmed-to-size foam box lid it came in, which was stuck to the frame plate by foam tape. The KK2 was attached to the foam by several loops of thread piercing the corners of the foam and looped through the mounting holes. You can make out the thread in the pic below. . .

Well. . . this worked GREAT for about three dozen flights. But then I noticed auto level just would not stay tuned in. Once I landed, put it in safe mode, and took off again, it would fly great for about one minute, then slowly start tilting back more and more till it took all my elevator stick up and to the left to keep it level. I was flustered. I looked it ALL over. Tilted mounts, loose props, loose motors in the mounts, loose boom screws, intermittent connections. . . all was good.

Then I spotted it, the corners of the foam had fatigued out and the board was able to move around on the foam fairly loosely. During all this I also noticed the flight time was greatly reduced, pretty much by a third. I thought ALL my batteries were crapping out on me. I suspect the vibrating and moving board was causing an undo amount of gyro and accelerometer activity and compensation to the motors.

I fixed it by merely removing the foam lid and just using another layer of foam tape, making it about 3/16" thick.

Anyway. . . my point is. . . a loose or vibrating board COULD be causing some kind of weird output to those channels.

 

[xuzme720]

One other suspect might be the props. Set up a single motor on a test stand and with a wattmeter run it up with both a forward and reverse prop and compare the readings.
I was doing some testing awhile back and found a couple of pusher props that pulled more amps than the standards...

 

[cranialrectosis]

Cyberdactyl, I thought I was nuts for mounting my KK2 the way I did. I too used the foam from the package and two sided tape. I pierced the foam and pushed small zip ties from the top down through the KK2, the foam and the bottom plate of the Anycopter. I then cinched up another zip tie under the bottom plate. I did this four times and then hand tightened all four at once so that the KK2 can't shift but the foam is not excessively compressed. Clip the ties and you have plastic nuts and bolts tailored to fit. Just don't tighten them too far or leave them too loose.



Thread, that's really nuts. Anyway, my KK2 doesn't move.

Props. I am just learning to fly. If I can't have colored props, I may as well whack this thing with a sledge hammer now and at least save one of my wife's rosebushes.

1450 kv motors on a 3S battery and 8" el cheapo cruddy props because I can get them in yellow and my old fogey eyes can still see yellow.

Based on another thread, I am looking into CF or reinforced props that I may be able to paint. I understand the need to score the props first and then paint and then balance them.

At this point, I have no doubt that I am warping props to high heaven at 50% throttle. I have no idea if this matters but home for me is 6,300 ft above sea level. I have to push a bit harder than the FT guys.

 

[Cyberdactyl]

I think yours is better, not relying on the corners of the foam.

 

[xuzme720]

I like the color scheme! My anycopters are all wood colored!

 

[cranialrectosis]

Thank you both, and Tritium and Mustang for your thoughts on this.

The copter is purple because purple is my wife's favorite color and I fly in her garden, through her trees and over her roses. Purple made the sale easier. So long as my flyers are purple and don't become flying weed whackers, I have an acre in the city over which I may fly to my hearts content.

I have decided to disassemble the copter this weekend and rebuild it again. I can do better with the wire routing, I am considering shortening the booms by 1" (to better fit between the trees and make it less 'lanky') and I know I have something bent or twisted on this build causing the hot motor issue.

I will also replace that power distro board with a harness of my own making and move that receiver because it is ugly and throws off my CG by an inch.

This approach may never reveal the root cause of the hot motor issue. I have the booms, ESCs and motors numbered and I will not permit them to be assembled together in the same pattern. If the issue is not resolved at that point, I will order another KK2 (I will need a second someday anyway).

It's fall in Colorado. The wind is blasting 30mph, it is 22 degrees outside and USPS did not deliver my FT 3D yesterday.

Looks like a good weekend to stay indoors and rebuild the Flying Purple Squirrel Eater.

 

[xuzme720]

I like the moniker of FPSE! But please, no polka dots!

Do you have a wattmeter? I would still check the props for amp draw just to make sure you aren't rebuilding for nothing. I know you are changing it for other reasons but I'd hate for you to get everything done and find you still have the same issue. The only thing you haven't been able to change locations on are the props. That is the only variable that has stayed constant.

 

[cranialrectosis]

I have a watt meter but I don't know how to use it. I know how stupid that is. I will correct it today.

I have changed out the props for new props (3). My first suspect was a collet (I had a second collet let go mid flight ), so I swapped three collets and balanced and installed three new props. I have already rebuilt this copter (last weekend was build 5) due to this issue and the issue has not moved.

At this point, the only parts that were in this configuration for the last build are:
KK2
Receiver
Anycopter Hub Components
Two booms 1 & 2
Battery
Power distribution board
Rotor and Collette 1

Moved or replaced were:
Collettes 2,3,4
Rotors 2,3,4 (will piss me off if the fix is rotor or collette 1)
Booms 3 & 4 (cracks between the interior screw holes)
Delren struts with G10 mounts were repaired/rebuilt and rotated CW.
Motors 1-4 cleaned and rotated CW (except 4 which is new when I hosed up the old 3)
ESCs 1-4 rotated CW and new female bullet connectors
Splices (lengthen the leads) from the ESC to the female bullet connectors were re-built with new 16awg silicone wire.
Male bullet connectors from the motors all re-soldered (I found a cold solder on one so I re-made them all).
Receiver cables
Relocated Voltage alarm

Added:
Rubber grommets at the end of the booms to mitigate vibration
5V running and strobe lights with controller board and antennae
Mesh to hide wires

Still to do:
Replace battery plate with new FT Camera plate (paint and assemble)
Add switched 5V 'headlamps'

I have an idea for measuring rotor level. I think I will try this first and look for a motor or pair of motors slightly tilted. If that returns nothing I can replace/relocate collette 1 and rotor 1, the power distro board, the receiver and/or the hub. Likely in that order.

I am not yet willing to relocate the transmitter.

 

[xuzme720]

I have a watt meter but I don't know how to use it. I know how stupid that is. I will correct it today.

Don't let it get you down. Troubleshooting electronics is some of the hardest to do in a complex system like a multicopter...

Wattmeter or voltmeter?

The wattmeter will just plug in-between the battery and the harness. The voltmeter or multi meter can be used but it needs to be wired in series and is harder to use as it won't save the highest readings.
Let me know which one you have and I can walk you through it. If you only have a multimeter and some extra connectors/wire it's easy to build an adapter to get readings with the multimeter.

 

[cranialrectosis]

Leveling my rotors has determined that I sukked.

I have measured the distance from my level workstation to the tip of each blade on one rotor. I do this twice. The second time at a right angle to the first. I am looking for deltas. In theory, the measurements should be < 1/8" apart for me to consider it passable.

Three rotors show > 1/4" of delta. The last comes in at < 1/8" of delta.

For example, one rotor tip (a) is 3 28/32" from my level desktop. The other end (b) measures 4 4/32" from my desktop. The delta is 8/32" or 1/4". I spin the prop 90 degrees, measure again and subtract the lowest (a) from the highest (b).

I have no idea if the theory is sound but it seems good to me.

It also indicates that the issue is frame related and at the mount or motor. I know my booms are level.

I am now measuring in similar fashion the bottom of the collette, the base of the motor, the mounts etc... until I find where it is level and I will know where my culprit is hiding.

I think...

 

[cranialrectosis]

It is a battery balancer and watt meter. I have both the watt meter and a volt (multi) meter, but the watt meter is what I believe is what is needed to perform the test you are suggesting.

 

[Cyberdactyl]

As to measuring if the booms are level, make sure you're measuring the props are level AND concentric in the vertical or y axis. Concentric, each blade should be at the same height at the same spot. . . or within a couple of mm.

Level props are a bit harder in that they obviously should be parallel to the booms. Or the plane of the rotors should be parallel to the horizon. That can be determined by resting the booms on the same type of drinking glasses (insuring wire is not resting the on glass rims) or just insure the booms are level. Then taking a scale and determine if the height of the blades are at the same height at three points 120 degrees apart.

 

[cranialrectosis]

Cyberdactyl, you use very efficient syntax.

I will try the concentric test next.

 

[xuzme720]

If you have the wattmeter it is a simple matter to check the draw with both types of props.
Mount a single motor to something fixed so when you throttle up, it doesn't move or go anywhere. I will leave it up to you on how to do this since I don't know what you have on hand. It can be as simple as a boom clamped to a table.
Once you have a fixed stationary motor, hook it's leads to an ESC, and the ESC to a receiver or servo tester. This is so you can control the motor for the test.
Now plug in the wattmeter to the ESC, either directly, or if you are using a motor from the multicopter, use the harness to power the test rig. Now all you have to do is make sure the motor turns in the correct direction for the prop you are testing. Once you have motor direction matching the prop direction, secure the prop and run up the motor to full throttle and leave it there for a few seconds while looking at amp draw.
Then reverse the motor direction by swapping 2 ESC leads, and the swap prop to the opposite direction to match the now reversed motor and repeat the full throttle test. The amp draw should be very close to the same. If the amp draw is not close, say within a few amps, then likely the issue will be in the props and you will have no way of fixing that, other than testing each prop and selecting a set that matches as close as possible.

I wish I could give you pictures, as they would explain much clearer but let me know if any of this doesn't make sense.

 

[cranialrectosis]

Your instructions are clear and concise. I will get that done once I figure out what is shimming my motors or twisting the mounts. Could I have simply not drilled the boom holes straight enough?

My issue with the watt meter is that I have to swap out the Dean's connectors on the meter to XT60s like on everything else I have.

Been having too much fun flying, crashing and rebuilding this thing to get around to it yet.

I think the last test Cyberdactyl was suggesting has me understanding root cause. My motors are tilted by a few degrees each and that is wreaking havoc on my yaw.

I suspect root cause is similar to my own moniker...

 

[xuzme720]

Tilt will do that since if the motors are inducing yaw that the FC board has to continuously counteract, then it will be working those motors VERY hard.

On another note, if you use XT60's and your wattmeter has Deans, just swap the Deans for XT60's. My wattmeter came with no connectors at all so I had to install them anyway...

 

[cranialrectosis]

This problem is resolved.

Root cause is my mounts not being parallel to the horizon causing my rotors to not be parallel to the horizon. The cumulative effect of three rotors being off seems to have caused the yaw issue.

I have temporarily resolved the issue with shims. I rolled up little wads of electrical tape (see Mustang, I told you it still had a use) and stuffed it between the bottom of the motor and the mount on the low side until the rotor tips were the same distance above my desktop at 0, 90, 180 and 270 degrees.

Copter flies the best it ever has and is the quietest it has ever been.

Cool because my FT 3D has arrived and I am eager to go build it!

Thank you all for your encouragement and support.

 

[xuzme720]

Glad to hear it was tilt and not props. In this case I am more than happy to be wrong!

 

[Cyberdactyl]

It is perplexing though that a very subtle tilt of a prop(s) could cause the motors and ESCs to run markedly hotter than the others. If that were the case, why doesn't the rear motor on an active tri get overly hot?

 

[Craftydan]

Because standard quad yaw is all in the CW/CCW motor imbalance.

In your tri, altitude is maintained by keeping all three close to the same thrust, and yaw is thrust vectoring off the rear. To stay level with a slight yaw, the rear motor will only need a slight increase in thrust for what's lost to feed yaw.

For a quad to do the same it had to reduce one pair and speed up the other, using the difference in motors' torques to twist the airframe. If it's got a natural yaw from misalignment, then there is a slight thrust vector. At the end of those long arms, a small thrust vector becomes a LARGE torque on the CG, which requires a large differential in motor thrusts to get a matching torque. This gets worse with longer booms.

Effectively, a small-but-enough twist can force your quad to fly on two rotors and not four, with the other two spun up just enough to keep balance. This is likely the case here.