CranialRectosis' Twitchity Mini-Hex build

[cranialrectosis]

I have stripped off the rotors and have been running the motors separately in Baseflight after getting all the new KISS 18A ESCs attached.


My maiden for this rebuild was less than impressive. I encounter a vibration that shudders the whole frame every 2 seconds or so that makes the copter really hard to hover. You can hear the vibration run through the long, thin G10 booms like a tuning fork.

In this video, you can hear the pulses vibrate the XT60 plug on my workbench. I haven't noticed it yet with any single motor so I am unsure as to where this is coming from. I think this is an unbalanced motor or maybe two hitting some kind of harmonic...

The issue comes and goes as I increase throttle and is most prominent at <> 25% which is right where this thing hovers.

 

[cranialrectosis]

I sent some photos to Flyduino showing successful builds and some popped ESCs.

I don't know if these will help but if anyone knows why certain components pop I am interested. I.E. what causes a capacitor or a FET to pop.

 

[Twitchity]

It looks like you have nice clean solder joints, and shrink wrap around the CF boom so the ESCs don't short out. Not sure why they popped on you. Hopefully Flyduino will be able to give you more insight and replace a few for you. My ESCs are mounted the same way on my quad and I didn't have any problems with them (yet).

 

[cranialrectosis]

With a little help from Mustang last night, I may have isolated motor 5 as the problem. When I run the motors indavidually from Baseflight, and let them run for a few seconds at a constant speed <> 25% throttle, motor 5 sounds different and seems to hum i waves a bit.

I don't know if it is the connection to the ESC (bad solder joint) or a bad/bent Sunnysky.

I plan to re-solder the motor to the ESC and try again and if that won't work I will replace the motor and see if the vibration goes away.

If anyone has insight into why different components might burn out on an ESC, I am very interested. I concur with jhitesma that my challenges with these are out of proportion and am looking for things I might be doing to cause the burn outs and motor twitches.

Twitchity, are you running Cobra motors or Sunnysky motors? I am thinking I may have enamel flowing back into the solder joints on my Sunnysky motors. I have never heard of anyone having problems with Cobra motors unless they cut the motor leads short enough to be into the winding wires.

I'd love to get this running. I could use the snowblower.

 

[Twitchity]

I'm running the Cobra 2300's on my hex with KISS ESCs. I cut the heatshrink where the winding leads meet the braided wires, de-soldered the joints and soldered the winding leads to the ESCs. Those little pads were hard to solder with the FET being right there, but I think I got a pretty solid connection.

 

[cranialrectosis]

"my hex with KISS ESCs"

Have we seen that build?

 

[Twitchity]

I meant to say quad I get caught up with wanting to build a hex, but that will have to wait until after the holidays.

 

[cranialrectosis]

Is there any way to balance a Sunnysky or do I just need to replace the motor(s)?

A zip tie is never gonna hold and is probably too big.

 

[Twitchity]

How bad is it out of balance? Maybe you can use some form of epoxy or jbwelb on the bell of the motor similar to how prop hubs are balanced to help even it out? That's all I have for right now

 

[cranialrectosis]

In this clip, the copter is placed on a roll of packing tape so that the screws/nuts that attach the booms to the center plates are sitting on the cardboard roll and/or the tape. The tape roll is pretty solid and conducts vibration into the table and allows the lipo strap to hang freely and not interfere.

Each motor is spun up in sequence as the Naze sees it, 1-6. Then all 6 simultaneously. The motors in each test are spun up to 1501 (midrange) for a few seconds and then returned to 0.

The sound you hear is the vibration from the motors conducting through the booms, the tape and into the 3/4" plywood desktop that resonates like a drum skin. The copter does not hum like this in the air but you can see the effect of the vibrations and feel it in the sticks.

The low frequency vibration has a frequency in itself making me think I have multiple motors out of balance. When it peaks, the whole copter shudders.

The camera is paused on motor 4 and I linger at 1300 (about where this copter hovers). Baseflight clearly shows movement on the accellerometers at this point. Motor 5 also makes low frequency vibrations but higher up the power curve.

My suspicions are on motors 4 and 5.

I wonder if Altitude has any Cobras.

 

[cranialrectosis]

How bad is it out of balance? Maybe you can use some form of epoxy or jbwelb on the bell of the motor similar to how prop hubs are balanced to help even it out? That's all I have for right now

I was thinking electrical tape to find where to add the balance and then epoxy once I find the magic spot. I don't know that tape will make a difference though.

 

[Twitchity]

What about hot glue to find where to balance them? If altitude doesn't have the Cobra's, multirotorsuperstore has the 1960kv and 2300kv in stock.

 

[cranialrectosis]

Hot glue...good idea.

Cobras are on order and should be here in a few days.

 

[jhitesma]

Found this interesting last night. I finally took the emax 1806's on my emax 250 apart to clean them after a few sandy landings...and found it was instantly obvious how they balanced them:





Ok, maybe not instantly obvious...at first I thought my daughter may have shoved some laffy taffy in there when I wasn't looking and it melted around the magnets. But upon closer inspection it appears to be some kind of epoxy which I have to assume was there to balance the bell.

 

[cranialrectosis]

I had trouble with some Maytech motors that pinged as they spun. I opened them up and found a similar blue gunk inside so I cleaned it out of them. The pinging stopped but the motors were then so out of whack, I have never been able to get the MW to fly well. I thought it was some type of packing screwup...


On a brighter note, I ordered motors from Altitude Hobbies Wednesday, they are delivered on Thursday. Way to go Garrett!!!

 

[Balu]

That's just like they put weights on the inside of alloy wheels. I always wondered if there's some balancing tool that shows you where to put weight and how much. - just for the motor and for the props too.

 

[cranialrectosis]

That's just like they put weights on the inside of alloy wheels. I always wondered if there's some balancing tool that shows you where to put weight and how much. - just for the motor and for the props too.

Twitchity suggested a drop of hot glue and spin the motor trial-and-error type test but with 3 of 6 motors in question and only 1 spare left, I went with Cobras to be done with it. A bell balancing tool, if inexpensive, would have had an impact on this decision.


Another update.

I engaged Flyduino tech support to ask why these ESCs burn out. After looking at the photos, I was given these suggestions; always use a lipo, never solder when connected to power, be careful of ESD and isolate them from carbon fiber.

I will take more stringent precautions for ESD as I live in a remarkably dry climate. The rest were never in question. I am not sure what other than a lipo I would use and who solders to a hot circuit?

Also without me requesting it, Flyduino is replacing 5 of my 7 failed ESCs. I am going to re-attempt the 2 they are not replacing just on general principal.

Flyduino has always delivered for me in the past. This customer service exceeds my expectations.

 

[jhitesma]

That's just like they put weights on the inside of alloy wheels. I always wondered if there's some balancing tool that shows you where to put weight and how much. - just for the motor and for the props too.

Dynamic balancing machines exist, but I haven't seen them on the consumer market for hobby sized stuff. Just go down to your local automotive tire shop and I'm sure they'll have a dynamic balancer, spins the tire - then stops with the light spot up and reads out how much weight the tech needs to add. Repeat once or twice and they're good.

I believe e_lm_70 who posted on here a few times made a small hobby sized balancer at one point - but his setup was a bit fiddly and not exactly user friendly. Yeah...here's his project post on RCGroups: http://www.rcgroups.com/forums/showthread.php?t=1913379

I'm really kind of surprised that China hasn't pushed out some kind of dynamic balancer aimed at hobyists.

 

[Balu]

That's exactly what i was thinking about. Perhaps scaling down and increasing the RPM doesn't help with detecting the sweet spot. But after seeing how they balanced the bells, I'm fairly sure something like this has to exist too. They wouldn't just put epoxy in there by trial and error as we do with stickers...

I remember e_lm_70's tool. It's a nice helper to measure vibration at specific speeds and makes it easier, but it's still not as sophisticated as it should be

 

[cranialrectosis]

I have the new Cobras all connected to KISS ESCs. I got all the motors tested for direction, all the ESCs synched and the motors spin up in unison using motor test in Baseflight.


I disconnected Baseflight, disconnected USB, disconnected the lipo and turned off my transmitter. I slid all the heatshrink in place and turned on the transmitter, connected the lipo, armed the copter and spun up the motors just a bit. Instantly smoked a KiSS ESC and a Cobra...



From Baseflight in motor test, this motor and ESC spun up just fine.

Any suggestions?