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Old May 20, 2012, 02:14 AM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Aberdeen
Joined Mar 2006
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Look what I found when i went to swap out the motor on my HK Slick:


I've heard of metal fatigue causing this type of failure and I had noted that the Scorpion cross mount was a bit narrow where the mounting screws pass through, but I was still shocked when I discovered this. I cant believe how lucky I was not to have lost the motor in flight. I'm sure it would have departed on the very next flight.
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Old May 20, 2012, 02:28 AM
bryansifsof44's Avatar
United States, AK, Anchorage
Joined Oct 2011
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Quote:
Originally Posted by stgdz View Post
Not sure about it. I really like the speed that the 13" prop gives, it really feels like a perfect balance between the 14" and 12". The extra really likes this prop also.


also jim, the two motroflys that I got yesterday, here are the numbers

2820-750
14x7 APCE
watts 800
amps 50
rpm 8800

2820-600
13x6.5 APCE
watts 750
amps 40
rpm 9600

I saw 10k in the air on the 600 for rpms, DAYUM! 750 never crossed 8800.



Regarding batteries, these are the two I am looking at
http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html
http://www.neumotors.com/store/page10/page10.html 5s 2100

The guys running their hotliners use the neu battery
Like I said I spent more time on the 13x6.5 and I will not compromise from the benefits of the 14x7 prop on 48" exps... And speed is still darn respectable. Your RPMs are close to what I have (8900) but the watts and amps you have are lower then what I got (920watts @ 59 amps).
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Old May 20, 2012, 02:37 AM
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Cabledawg1's Avatar
USA, VA, Newport News
Joined Jan 2010
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Quote:
Originally Posted by JetPlaneFlyer View Post
Look what I found when i went to swap out the motor on my HK Slick:
I've heard of metal fatigue causing this type of failure and I had noted that the Scorpion cross mount was a bit narrow where the mounting screws pass through, but I was still shocked when I discovered this. I cant believe how lucky I was not to have lost the motor in flight. I'm sure it would have departed on the very next flight.
Thats normal....Ive lost 3 motor mounts on my 48" Extra. They crack and break....and yet will still fly allmost normally. The pressure holds in it place even though its broke. Ive learned to check my mounts every few flights. There is a sound the prop makes when some of the mount is broke....it allmost sounds like the prop is out of balance, but just a tad. Im sure there are guys flying their 48" EF planes now with broken mounts. but dont know it.
I just got 2 of these...they are the same size as the Torque (maybe made at the same factory for all we know).....this will be my 4th motor mount
http://www.innov8tivedesigns.com/pro...fc445f4e33a09e

If they made a carbon mount, I would be all over it
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Old May 20, 2012, 04:41 AM
Team Hillbilly (UK)
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United Kingdom, England, Cambs
Joined Oct 2011
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Lucky catch Steve
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Old May 20, 2012, 08:29 AM
Not as Good as The Kid
Aeroplayin's Avatar
South Pasadena, FL
Joined Sep 2009
6,885 Posts
Quote:
Originally Posted by JetPlaneFlyer View Post
Look what I found when i went to swap out the motor on my HK Slick.

I've heard of metal fatigue causing this type of failure and I had noted that the Scorpion cross mount was a bit narrow where the mounting screws pass through, but I was still shocked when I discovered this. I cant believe how lucky I was not to have lost the motor in flight. I'm sure it would have departed on the very next flight.
This is why we went to the G10 cross mounts on the Motrolfly. I originally got the G10 from my local distributor who cut them himself on a CNC for his clients because the combination of the Motrolfly power and the bigger props it can swing were hammering the metal mounts. Tom broke two before switching over.

As for the batteries, we stopped using Zippy Flightmax a while ago for the same reason. The sag after 20 cycles was significant and when the volts drop, so does the RPMs, and when you're not getting the RPMs, you're not getting the power.

I tested a new battery on the Q80 Hacker yesterday and got 35.97v on the first try to WOT, which is 6450 RPMs on the 210Kv. The Sky Lipo spun the same prop on the same motor to about 6635 RPMs. Now they are both brand new packs so I'm expecting to see some settling-in and more power. But the difference in power now is 0.5 HP at WOT illustrating how much of a major part the battery plays in peak performance.

Try charging the old Gens and the new Zippy to full and equal charges, then try them both on the same plane and see what the volts are at WOT. If you can keep them wide open for the same amount of time, get a reading on the ending voltage too. It would be interesting to see how they compare even though it's not a fair fight.
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Old May 20, 2012, 08:33 AM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Aberdeen
Joined Mar 2006
11,765 Posts
So i thought that it might be a good idea to check over my Motrolfly in the Edge too. Good job i did; right away I noticed a lot of radial play on the rotor, as if the bearings had gone. Turned out it wasnt the bearings, it was the stator holder which had worked loose from where it presses into the rear mount. It's held with set-screws and these were still tight but the stress from the big prop had caused fretting between the two parts where they press fit together.


Also (and i dont think connected with the above problem) the shaft and/or rotor can has been flexing and the magnets have been rubbing on the stator


Looks like Ken at Subsonic was dead right to be concerned about running a 14x7 prop on the new 750kv wind of the DM2820. It seems that it's just not structurally strong enough to take the load from the big prop in 3d type flight.

I've Loctited the stator holder into the rear mount and it seems to have done the trick, I'll be running a 13x6.5 from now on. I was running a 14x7 APC, maybe a lighter wood 14x7 might be ok but you would need to keep an eye out for the same problems that I experienced.

Steve
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Old May 20, 2012, 09:09 AM
Not as Good as The Kid
Aeroplayin's Avatar
South Pasadena, FL
Joined Sep 2009
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Quote:
Originally Posted by stgdz View Post
also jim, the two motroflys that I got yesterday, here are the numbers

2820-750
14x7 APCE
watts 800
amps 50
rpm 8800

2820-600
13x6.5 APCE
watts 750
amps 40
rpm 9600

I saw 10k in the air on the 600 for rpms, DAYUM! 750 never crossed 8800.
Some interesting Kv Efficiency differences:

Motrolfly DM2820
Kv: 750
Prop: APC 14x7e
Cells: 4S
RPM: 8800 RPM
Watts-in: 800W
Amps-in: 50A
Watts-out: 763
Amps-out: 47.7
KvE%: 73.33%
Airspeed: 58.3 mph
Static Thrust: 3.78kg

Motrolfly DM2820
Kv: 600
Prop: APC 13x6.5e
Cells: 5S
RPM: 9600 RPM
Watts: 750W
Amps: 40A
Watts-out: 669W
Amps-out: 35.7A
KvE%: 85.33%
Airspeed: 59.0 mph
Static Thrust: 3.35kg

It sees that the 750Kv setup on 4S was having a tough time swinging the 14x7 prop. While drawing 4v per cell, the 8800 RPMs is only 73% of the potential. On the other hand, the 5S setup was drawing 3.75v per cell and operating at a very good 85% efficiency.
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Old May 20, 2012, 09:15 AM
Not as Good as The Kid
Aeroplayin's Avatar
South Pasadena, FL
Joined Sep 2009
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Quote:
Originally Posted by JetPlaneFlyer View Post
So i thought that it might be a good idea to check over my Motrolfly in the Edge too. Good job i did; right away I noticed a lot of radial play on the rotor, as if the bearings had gone. Turned out it wasnt the bearings, it was the stator holder which had worked loose from where it presses into the rear mount. It's held with set-screws and these were still tight but the stress from the big prop had caused fretting between the two parts where they press fit together.

Also (and i dont think connected with the above problem) the shaft and/or rotor can has been flexing and the magnets have been rubbing on the stator


Looks like Ken at Subsonic was dead right to be concerned about running a 14x7 prop on the new 750kv wind of the DM2820. It seems that it's just not structurally strong enough to take the load from the big prop in 3d type flight.

I've Loctited the stator holder into the rear mount and it seems to have done the trick, I'll be running a 13x6.5 from now on. I was running a 14x7 APC, maybe a lighter wood 14x7 might be ok but you would need to keep an eye out for the same problems that I experienced.

Steve
Nice catch there Steve. I was working on my post when you posted yours and perhaps they are related. I may have to take a look at Tom's 683Kv working the 14x7 APC, but I'm going to guess that it's okay considering that it is still tight to the feel. But it does make any further 5S test with the 14x7 moot, IMO.
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Old May 20, 2012, 11:42 AM
bryansifsof44's Avatar
United States, AK, Anchorage
Joined Oct 2011
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Bummer about the motor Steve... Do you do a lot of hi gyroscopic maneuvers?
I have a couple of hundred pretty hard flights on mine... No issues so far but will keep a eye on it.
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Old May 20, 2012, 12:03 PM
Not as Good as The Kid
Aeroplayin's Avatar
South Pasadena, FL
Joined Sep 2009
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I put all the data I could find in a spreadsheet and thought I'd share. Some of the >4v per cell data may be skewed but the rest of it is actually very solid. Everything should be clear ... KvE is Kv efficiency, speed is right off the airspeed calculator for pitch and RPMs, St-kg is right off the static thrust calculator in kilograms. Comp-W and A is the percent of Watts and Amps consumed from in to out.

You can see why we all like our individual setups, why the 600Kv 14x7 on 5S is bit too much, and why the 14x7 on the 750 with 4S is pushing it too. If you take off the 5S and the 750Kv motors on a 14x7, you will see Tom's setup next in line when sorted by thrust. I'm going to throw it out there that the 683Kv with the 14x7 APC on 4S is the safest setup with the most power-out in the group. Maybe under 8500 RPMs is something to consider with the 14x7.

The 5S on the 600Kv with the 13x6.5 looks really good and then my 14x7 setup has the next set of good values. Take a look at thrust and speed relative to KvE and power consumption. I'm also a bit suspect of the row with the 4.0v per cell because of two things... we don't often see this type of voltage at WOT on a 14x7, and it is much different than the other 750Kv 14x7 row on 4S even though the RPMs are very much the same.
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Old May 20, 2012, 12:15 PM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Aberdeen
Joined Mar 2006
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Quote:
Originally Posted by bryansifsof44 View Post
Bummer about the motor Steve... Do you do a lot of hi gyroscopic maneuvers?
I have a couple of hundred pretty hard flights on mine... No issues so far but will keep a eye on it.
As my post stall control sucks I do tend to do more high energy stuff, but nothing more extreme than many others.

Bear in mind that my motor was the first of the 750kv DM2820's, I've been running it since December with the 14x7 APc on virtually all the time. There was no sign of any problem when I checked it a couple of weeks ago, but you wont see any signs of the magnets rubbing unless you pull the motor apart, so unless you have done that then you cant be sure there is no problem.

I think it's all fixed. Loctite is great stuff and seems to have done the trick in taking out the slop that had developed in the stator holder to rear mount joint. The only thing to prevent the magnets rubbing is to use a lighter prop.
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Old May 20, 2012, 12:31 PM
VOLTS > AMPS
stgdz's Avatar
United States, MN, Buffalo
Joined Jul 2011
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Quote:
Originally Posted by Aeroplayin View Post
I put all the data I could find in a spreadsheet and thought I'd share. Some of the >4v per cell data may be skewed but the rest of it is actually very solid. Everything should be clear ... KvE is Kv efficiency, speed is right off the airspeed calculator for pitch and RPMs, St-kg is right off the static thrust calculator in kilograms. Comp-W and A is the percent of Watts and Amps consumed from in to out.

You can see why we all like our individual setups, why the 600Kv 14x7 on 5S is bit too much, and why the 14x7 on the 750 with 4S is pushing it too. If you take off the 5S and the 750Kv motors on a 14x7, you will see Tom's setup next in line when sorted by thrust. I'm going to throw it out there that the 683Kv with the 14x7 APC on 4S is the safest setup with the most power-out in the group. Maybe under 8500 RPMs is something to consider with the 14x7.

The 5S on the 600Kv with the 13x6.5 looks really good and then my 14x7 setup has the next set of good values. Take a look at thrust and speed relative to KvE and power consumption. I'm also a bit suspect of the row with the 4.0v per cell because of two things... we don't often see this type of voltage at WOT on a 14x7, and it is much different than the other 750Kv 14x7 row on 4S even though the RPMs are very much the same.
Looks great, now I think I may pull my 2820 though from what steve has shown. I've been on 5s about a month and like to go hard and fast with it. Full speed tumbles in the mxs are just great.
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Old May 20, 2012, 12:40 PM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Aberdeen
Joined Mar 2006
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Quote:
Originally Posted by stgdz View Post
Looks great, now I think I may pull my 2820 though from what steve has shown. I've been on 5s about a month and like to go hard and fast with it. Full speed tumbles in the mxs are just great.
It's easy enough to separate the stator from the rotor, just remove the collar from the shaft (I had to drill out the set screw to remove it).. Then the rotor should pull off retained only my the force of the magnets.

On my motor the collar had also slid back slightly on the shaft which meant that the rotor was pulling out under load.
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Old May 20, 2012, 03:41 PM
VOLTS > AMPS
stgdz's Avatar
United States, MN, Buffalo
Joined Jul 2011
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And when you say play you mean grabbing the spinner and being able to move it up and down slightly.

Because if so I can do this in one position. Rotating the prop moves the position.
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Old May 20, 2012, 04:15 PM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Aberdeen
Joined Mar 2006
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Quote:
Originally Posted by stgdz View Post
And when you say play you mean grabbing the spinner and being able to move it up and down slightly.

Because if so I can do this in one position. Rotating the prop moves the position.
Yep. that's what I mean. Mine was the same, it moved more in one direction than in the other, that's because the set screws placed 180 deg apart stopped if moving much in one direction. It may have been a better idea to have them 90 deg apart?

Take the cowl off and see if the gap between the rear of the rotor 'bell' and the back plate opens and closes when you 'waggle' the prop driver .. If so that's a sure fire indicator that something is amiss.

I'll cross my fingers that it's a false alarm

Steve
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