Author Topic: Start spin-up transition vibration? (Read 5017 times)

Dennis Toth · « **on:** August 14, 2011, 05:36:22 PM »

Guys,
I've been working with testing the re-pitched Zinger 12x6 wood prop and have experienced a rather strange vibration during start spin-up at about the 80% power point (AXI 2826/10, 4S1P pack). I noticed this on a ground test and it is pretty wild vibration that the motor goes though, then smooths. This doesn't happen on every start and not at all that I recall on the APCE prop. The ESC is a CC 45 set for soft start. I've check the prop balance and its dead on and once it passed through that point its fine. Anyone else see this and what can be done to eliminate it as it is a rather strong shaking on the airframe for the couple seconds it does it.

Best, DennisT

Wynn Robins · « **Reply #1 on:** August 14, 2011, 06:21:42 PM »

motor timing?

William DeMauro · « **Reply #2 on:** August 14, 2011, 06:51:51 PM »

Dennis,
Besides the timing, I'm curious as to which version of software you are using in your speed control?

Dennis Adamisin · « **Reply #3 on:** August 14, 2011, 06:58:43 PM »

Someone else has been having this EXACT problem with his Pletty - critical RPM about 7800 (sounds comparable to yours) THis other flyer has NOT had any luck fixing it - looking forward to what ever you find.

Tim Wescott · « **Reply #4 on:** August 14, 2011, 07:34:34 PM »

Do you have an RC setup or a servo tester that you can use to hold the thing right at the "bad" frequency? It could be that you're exciting a natural frequency of the prop or plane, or it could be some bad juju in the interaction of the speed controller and the motor.

Douglas Ames · « **Reply #5 on:** August 14, 2011, 08:20:43 PM »

FWIW my Dremel does the same thing at a certain rpm - hits resonant freq. I'm thinking worn bearings or end play? -or- Prop may be balanced but is the hole straight? OK I'll

...

Dennis Toth · « **Reply #6 on:** August 14, 2011, 10:36:35 PM »

William,
CC 3.29 for castle link. Timing is at 8, gain is at 28.

Best, DennisT

Igor Burger · « **Reply #7 on:** August 15, 2011, 12:25:37 AM »

I am not sure what you exactly means, but if it is screaming sound comming from MOTOR (happens also without prop at certain rpm), then I have information resulting from communication between us and AXI guis:

We have very specific use of those motors. Every outrunner has certain critical rpm which hits own resonantion frquency of the rotating bell. In case of AXI 2826/XX the rpm is somewhere at 9500rpm +/- something. We fly those motors at fixed rpm whole flights and for example old APC 12x6 prop works well at 9000 rpm what is very close to that critical rpm. If we fly at rpm where the bell wants to resonane, new motor will little ring whole flight. That sound is explorable during flight as a very silent difficult to hear clean ringing (clean means harmonic, no screaming etc). Long usage at this rpm, will kill both bearing and also the connection between bell and shaft. So early or later that ring will go to stronger and to mutlifrequency sound, resultig later to ugly scream at some rpm. Solution for this problem is new rotor and bearing. We fixed this way several motors, unfortunatly it must be done at AXI, because the shaft needs new washers of proper thickness with new or moved bearing, so it is not for amatheur work.

They told us that this is not problem of R/C flyers flying at wariable rpm. And BTW, this was reason why I use now new prop working at 11000 rpm :-)). An 3 blades is another thing which will save your bearing.

William DeMauro · « **Reply #8 on:** August 15, 2011, 07:21:01 AM »

Dennis,
Can you try a little test for me? Change 3 settings but only one at a time and test. First: Go back to 3.00. I'm curious if it goes away there. I had a Cobra and a power 25 do something similar on 3.28 and 3.20 but not on 3.00.
Second: Try your motor timing at 5.
Third: Set your PWM for 12
The last 2 are what my motors are set at after I changed back to 3.00.
My scorpion is at 3.20 with zero issues so i leave it alone. I know of a few other people with power 25's that are at 3.20 with no issues so I cant explain the one that wants to run at 3.00.
William

Dave Adamisin · « **Reply #9 on:** August 15, 2011, 01:13:57 PM »

If you change the prop does it still happen? It sounds like a tortional vibration period. A natural frequency of the motor shaft or fuse set off by a combination of the prop weight/load and the critical speed it shows up at. If it's a transient (stops after it speeds up or down from the vibration speed) than it's probably just a rpm to be avoided.

Tim Wescott · « **Reply #10 on:** August 15, 2011, 01:34:40 PM »

If you've got another motor with similar capabilities that'll bolt in, try it -- if the problem follows the motor, look at the motor.

Ditto, try it with the prop off. If the problem follows the prop...

Ditto, try it on a test stand instead of the airframe. If the problem follows the airframe...

Dean Pappas · « **Reply #11 on:** August 15, 2011, 09:33:15 PM »

Hi All,
I'm inclined to start testing based on Dave's conjecture. You already said that the APC doesn't do it.
You may have a dynamically imbalanced prop that is still statically balanced.
Alternatively the prop's mass and flexibility just may have a natural resonance that agrees with the resonance Igor cited ... then all sorts of poop happens.
Dean P.

Dennis Toth · « **Reply #12 on:** August 16, 2011, 08:45:27 AM »

Guys,
Thanks for the input, I checked a few things yesterday to start to narrow down the problem. The motor does not have a problem with the APCE - 12x6P. The Zinger 12x6P weights just a C hair less than the APCE. The Zinger was heat pitched to match the lap time of the APCE. I have had the motor spinup smoothly a couple times with the Zinger but I removed it and remounted before the next start. One thing that might be a problem is the shaft hole enlargement. I used a tappered reamer (I've used this same reamer on dozens of other props) and somehow may have either finished with a rough cut or could be slightly over size that you don't feel but when the prop is tightened it moves off center.

Does anyone know if a pilot drill with a 1/4" pilot and drills to 5mm exists (Jim Lee's or Grainger tools?) to allow accurate 5mm drilling of the prop hole? Barring finding an accurate drill I will try a second Zinger and see if it makes a difference. If that doesn't work I'll start down the above mentioned settings list.

Best, DennisT

Howard Rush · « **Reply #13 on:** August 17, 2011, 08:10:08 PM »

Sounds like the dynamic instability that washing machines get at the start of the spin cycle. I should know something about this, but I don't.

frank williams · « **Reply #14 on:** August 17, 2011, 09:32:42 PM »

I've had this happen with several different props. Sometimes, just loosining the prop and retighten will reseat the collet such that it goes away. Its on the way up in rpm and sometimes will even happen on the timeout warning phase.

Igor Burger · « **Reply #15 on:** August 18, 2011, 01:17:35 AM »

Dennis, it really looks like dynamicaly unballanced, try to run the motor at low rpm and check if prop tips go the same path. It is necessary to check it after each pitch primming, it can easy move the blade to improper angle.

Dennis Toth · « **Reply #16 on:** August 20, 2011, 11:55:57 AM »

Guys,
I think I found the problem, the bearings are worn. I removed the motor from the ship and could feel the bell moving back and forth. The motor has about 300 runs on it. I will put it on the test stand and compare it to another motor with the same prop.

Best, DennisT

William DeMauro · « **Reply #17 on:** August 20, 2011, 01:16:38 PM »

Hi Dennis,
I found these 3 bearing links over on RCGroups. I think they may be useful to you and others out here. The first place sells ceramic bearing kits for some of our more popular motors. The prices seem very reasonable. Prices seem to drop when you click on the item too. http://www.rc-bearings.com/catalog/
http://www.avidrc.com/
http://www.vxb.com/

Dennis Toth · « **Reply #18 on:** August 20, 2011, 04:24:01 PM »

William.
Thanks, have you changed bearings in these motors? How do I pull them without heating the cast (I am used to pulling them on IC's by heating the case, no winding to worry about)?

Best, DennisT

William DeMauro · « **Reply #19 on:** August 20, 2011, 08:21:18 PM »

Hi Dennis,
I changed the bearings in a Scorpion motor. There is a good video here on how to do it in a Scorpion. ! . Most of these motors are very similar, I'm pretty sure this will be helpful. There are some other good how too video's at the bottom of this page that may help you and others with maintenance of outrunners. http://www.innov8tivedesigns.com/ . Hope this can help.
William

Dennis Toth · « **Reply #20 on:** August 22, 2011, 10:21:09 PM »

William,
Thanks for the video link, it showed how to remove the bearing, I actually did it by holding the stator in my hand and used a small pin punch to tap out (with a small hammer) the back bearing (two in the 2826-10) and 1/4" long bolt to tap out the larger front bearing. It was very easy, I intend to get new ceramic bearings from Boca Bearing. One thing the you need to get for the AXI motors is a pair of "retaining ring" pliers with very close prongs. I got mine at Sears: model 47411, $19, they have interchangeable tips that you can adjust to get the tips touching which allow you to get the retainer clip out. Seems there is a bushing washer in back of the retainer clip and another one on the other end of the bell, they may ware causing some play and should likely be lubed once in awhile.

Best, DennisT

William DeMauro · « **Reply #21 on:** August 23, 2011, 02:24:27 PM »

Dennis,
If you didn't see it on the Scorpion site. They do sell a bearing lube for only a few dollars. One bottle will probably last most of us forever. http://www.innov8tivedesigns.com/index.php?cPath=70&osCsid=14f975d1848cb5824fbbd6a88eb3e5f1. I do oil my bearings every 40-50 flights, Not sure if its helping but it sure don't hurt. I've talked on the phone with Lucian Miller (owner of innovative designs, Scorpion importer) and he insists the lubricating these bearings helps.

John Cralley · « **Reply #22 on:** August 23, 2011, 03:05:28 PM »

Well I have now joined the club (vibration club that is). Yesterday I test flew one of my S-1 electric Ringmasters. This one after an outside that missed by about an inch or so. In this model the plywood motor mount is attached by two nylon 10-24 screws to make a kind of "breakaway" mount.

When the prop hit the turf the screws sheared and the motor detached (the ESC stopped the motor) and there was enough torque to cause the rudder to hit and also breakaway. There was no apparent damage to the motor, prop (APC thin 11x4.5 pusher) or the electronics. So a bit of super glue for the rudder and two new screws and we are ready to go again. For the test flight I set the timer (Hubin F-9) to one minute and I am glad for that. About 30 seconds into the flight the motor started vibrating and increasingly so with time. The Velcro strap holding the battery let go (I'm going to do a better mount for the battery!!) and the battery swung out like a rock on string. Luckily shortly later the time expired and I landed the plane safely.

On examination it appears the the bearings on the motor (Scorpion S 3014 1050Kv) are shot. Could have gotten dirt in the bearings form the crash or from one previous crash (guess I should have disassembled the motor and cleaned it after the crashes - poor judgment on my part maybe

). I have ordered a new set of bearings and a new shaft but in surfing for the bearings I have come across posts claiming that Scorpion bearings are no good and that is why they recommend using a lubricant (which I have NOT done).

The bearings are pretty standard sizes and I wonder if anyone knows a source for "good" high speed bearings (they are 5 IDx10 ODx4 and 5 IDx8 ODx2.5 MM) to use in place of the Scorpion ones?

The moral here may be to disassemble and clean you motor after any crash and to LUBRICATE the bearings if you are using Scorpion motors!!

Dave Adamisin · « **Reply #23 on:** August 23, 2011, 03:32:03 PM »

I just ordered some from Boca. Simple to use tool on their site to pick out the brg's you need. They have some they recommend for outrunner motors and even have a "pick your brg's" based on motor manufacturer and model. Good luck.

William DeMauro · « **Reply #24 on:** August 23, 2011, 05:02:53 PM »

"The moral here may be to disassemble and clean you motor after any crash and to LUBRICATE the bearings if you are using Scorpion motors"
Actually that should probably be done with any motor.

Crist Rigotti · « **Reply #25 on:** August 23, 2011, 08:28:08 PM »

Quote from: William DeMauro on August 23, 2011, 05:02:53 PM

"The moral here may be to disassemble and clean you motor after any crash and to LUBRICATE the bearings if you are using Scorpion motors"
Actually that should probably be done with any motor.

With my Scorpions, whenever I have a prop strike, etc, I change the bearings. It is easy to do. While I'm changing them I oil them too. I get my bearing from RC-Bearings.

John Cralley · « **Reply #26 on:** August 24, 2011, 08:12:43 AM »

Re the bearings: I ordered a set from Boca Bearings but the source that Crist list has much better prices.

http://www.rc-bearings.com/catalog/index.php?cPath=50

Dennis Toth · « **Reply #27 on:** August 24, 2011, 03:22:00 PM »

Guys,
I picked up new bearings from Boca Bearing in Delray Beach, FL (800) 332-3256 (www.bocabearings.com). They have hybrid bearing that are class 5 with ceramic balls, steel race, the total for the three for the AXI 2826-10 came to $32. There are standard steel bearing available I wanted to go to a little better grade. They are great guys and will work with you to fit your motor bearing needs.

I have checked the motor and it seems there was a place were the bell was brushing the stator. It was on the bottom area of the motor (based on the way this motor is positioned in the mount). I checked the old bearings and there seems to be about an .007 - .009" movement in the race. Not sure why the rub is only on the bottom but my guess is the clockwise rotation, outside corner and gravity seems to team up to pull the bell down on the stator. I suspect I am really lucky that I had the ground problem when I did that caused me to look into the motor, a few more flights and I'm sure it would have caused major problems.

I will put the new bearings in tonight and hope to put the motor on the test stand and see if this fixes the problem.

Best, DennisT

Dennis Toth · « **Reply #28 on:** August 24, 2011, 08:30:06 PM »

Guys,
I just finished replacing the bearing in the AXI 2826/10. It runs fine starts smooth but there is a little step in the start, could this be firmware related? How do I check the firmware version I am running in CC?

Did a second run test with APCE 12x6 P repitched to 5, just the edge of the hub cuff removed, 9200 rpm, 4S1P TP 3900 pack, very smooth start still a little step but no vibration, static amps were 31.4 this is down from 35.6 prior to the bearing replacement. Seems we should keep a running history of static amps with the same setup as a way of assessing motor health.

Best, DennisT

Dean Pappas · « **Reply #29 on:** August 25, 2011, 10:02:58 AM »

Hi Dennis,
I don't know what you mean by a "step" but the static amperage will probably tell you more about battery health than about the motor.
Dean P.

Dennis Toth · « **Reply #30 on:** August 25, 2011, 10:34:37 AM »

Dean,
The "step" is just a spot where it seems to throttle up to full power/rpm. On the static amps condition assessment I agree about the battery but if the amps seem to increase with several batteries (which mine did) it's a tip off that something has changed. For my motor it seems that it was just starting to rub against the magnets and was robbing power from the prop. I got lucky, next thing would likely have been a magnet coming lose . Another indicator would be to check for shaft horizontal movement. I never did this until the problem occurred, knowing what I now know will make that check periodically too. Seems like some simple thing will keep us from planting a ship for a preventable problem.

Did another static prop test with the wood Zinger 12x5 that I was testing when the problem started. This time the motor spun up about the same as with the APCE there was the "step" but was not shaking. Seems the new bearings did the trick.

Best, DennisT

kenny stevens · « **Reply #31 on:** August 31, 2011, 01:48:50 PM »

Hi fellow elc stunt guys, I had this same vibration eat the nose off my 011 S/V-22 . The plet. was front mounted and the mount was not strong enough . The cure was to reinforce the mount plate. The vibration shoes up on most elc. airplanes but I plan to rear mount the plet.as it is running hot with this reinforced front plate.

Dennis Toth · « **Reply #32 on:** August 31, 2011, 03:47:59 PM »

Guys,
I am planning to add the external support tail bearing to my ship, I just ordered the shaft assembly which for the AXI motors is called a "Radial Mount Set". If you try to do searches for prop drives or rear prop assemblies you will not find it for the AXI. Use the radial mount set terminology and boom there it is. I now have to get the bearing that matches this shaft. I am hoping to get not only better motor support but better flight results by eliminating any yaw movement of the motor/prop during hard corner maneuvers.

Best, DennisT

Author Topic: Start spin-up transition vibration? (Read 5017 times)

Dave Adamisin

Dave Adamisin