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Old Dec 09, 2014, 10:40 PM
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I am looking for a motor for a kit that I have ordered, an Oculus EXL from MM Glider Tech, 130" wingspan. I am told that the all up weight should be 71 oz. I am planning on flying the glider in ALES. I am thinking that the Gliderdrive 3858 4.6 840 kv on a 3s battery 50 C or greater with a 14X8 or 14 X 9.5 prop would work. Does this sound reasonable/good setup for the application? If not any suggestions for alternate setups with this motor or suggestions for another motor would be appreciated.

Thanks
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Old Dec 09, 2014, 10:54 PM
WAA-08 THANK FRANK!
JimNM's Avatar
Las Cruces, New Mexico, United States
Joined Jun 2002
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I fly the Mystique on that motor with the stock 14x8 eflight prop. It needs a 4s battery to reach 200m before 30 seconds (22 seconds average). On 3s, I am about 180m on a good climb.

The stock Mystique prop does give better climb than the graupner 13x10 that I originally used.

I predict that you will want to run 4s instead- I am about at 55amps on 4s flying from 4000 feet ASL.. HTH
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Old Dec 15, 2014, 04:25 PM
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dharban's Avatar
Tulsa, OK
Joined May 2004
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I have attached a graph of performance data from a test of the GliderDrive motor. The test was a 30 second motor run using a 13x7 RF propeller on a 26mm Vladimir offset hub using a Thunderpower 2250 4S 45C battery pack. A thermocouple was inserted in the stator (coils).

The motor output after the initial voltage drop was about 640 Watts. Amperage was about 45 Amps and I measured a 50 degree temperature rise to a maximum temp of about 126 degrees F.

Propeller RPM was approximately 9750 and I had previously dyno-tested the prop and measured about 450 watts to drive it at 9750 RPM. Motor to propeller efficiency is in the range of 70 percent.

I would make the following observations about using this motor in ALES and F5J applications:

1. This motor is capable of delivering substantially more power than is necessary for most of the 3.5+ meter planes that are commonly flown in ALES and F5J. (I get satisfactory performance with less than 450 Watts on an 1.8 Kg Maxa).

2. Personally, I would not use Aeronaut propellers in this 4S application, especially with an offset hub. At full power, this combination is really honking and I prefer the higher rated RF propellers. I have blown up Aeronauts in similar service. The price savings is not enough to offset the risk of destroying a plane and/or injuring someone.

3. If you use a standard 42mm (between the pivot pins) hub this setup will draw a little more power and heat the motor up a bit more.

4. The 50 degree temperature rise is not at all alarming, but it wouldn't hurt to allow the motor to cool a bit before repeating a run -- especially on a hot day. That said, it is not likely that you will run this setup for the full 30 seconds in actual competition applications -- more likely 20 seconds or less.

5. This motor seems to have a little higher Kv than the comparable MVVS 4.6/840. It may take a slightly bigger prop to get the same power out of the MVVS, but it should have very similar properties.

6. I ran this test using a 2250 4S 45C pack because it was what I had on hand. It is likely that a Thunderpower 850 4S 70C or certainly a Thunderpower 1300 4S 70C pack would deliver nearly as much power with a substantial weight savings.

Honestly, for most applications these inexpensive motors (the GlideDrive and the MVVS) should work very well in most ALES and F5J applications. They are a bit heavier than optimal selections and will present a few more difficulties in achieving balance in long nosed planes, but I would select either one in a heartbeat over anybody's cheap geared in runner (The GliderDrive actually weighs slightly less than the Great Planes Inrunner and Gearbox).

Happy Landings,

Don
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Old Dec 15, 2014, 07:39 PM
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ddruck's Avatar
Canada, ON, Pickering
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Don with the discussion here of couple of these motors, your tests were run on what specific motor?

if the discussion is on 840kv, why not run it on 3s with a larger prop and still get 450w which seems to be enough even for a 4m glider.
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Old Dec 15, 2014, 08:42 PM
Flying = Falling (Slowly)
dharban's Avatar
Tulsa, OK
Joined May 2004
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Quote:
Originally Posted by ddruck View Post
Don with the discussion here of couple of these motors, your tests were run on what specific motor?

if the discussion is on 840kv, why not run it on 3s with a larger prop and still get 450w which seems to be enough even for a 4m glider.
This test was run on the 840Kv, although it seemed to test out a bit higher than its nominal rating.

It is important to understand that my test results reported both Input Watts and Output Watts. The measured INPUT WATTS were about 640 watts. (Input Watts =Input Amps x Input Volts) And this is the wattage most commonly reported in forums like this. I have a setup which allows me to measure Input Watts and Output Watts (Output Watts = Shaft Power Delivered To Propeller). Motor Efficiency = Output Watts/Input Watts. On this test the Motor efficiency is about 70 percent (not bad) or an Output Power of about 450 watts. More importantly, the Input Amps are close to the motor's 45 amp limit. While manufacturers' listed maximum amperage can be based on many things, I consider the operating limit based on the temperature rise that you measure during an extreme ALES cycle. In this case I measured about a 50 degree F increase from the 73 degree F starting temperature. I fly in a hot climate much of the time and assume a starting temperature of 100 degrees F. Based on the measured performance of this motor I would estimate that on a hot day the maximum motor temperature might approach 160 or so degrees F. While I have read that some of these high performance motors can go to 200 degrees F without damaging the insulation or magnets, I would judge this motor to not necessarily be constructed of the best materials and, at least for me, I would not run it at more than 45 Amps on a 4S setup.

As to why I did not run it on a 3S setup with a bigger prop, actually I plan to because I like big slow props and I don't need the power. It is not possible to simply connect a 3S pack and slap on a bigger prop and get the kind of performance you are suggesting. I have tested this setup and the efficiency of this particular motor drops off fairly rapidly as you push it on 3S. With 45 Input Amps, the input power is about 450 watts. But the efficiency at this operating point drops to 55-60 percent resulting in Output Power in the range of 250 to 270 watts. So even if you could push the motor beyond 45 Input Amps (which is probably not a smart thing to do) you have reached a point of diminishing returns with regard to Output Power. As much as I like the increased efficiency of larger, slower propellers, in this application you are not going to come close to converting the shaft power of the 3S setup up to the shaft power of the 4S setup.

All of this being said, the most important parameter here is probably Input Amperage. It may be a coincidence, but it appears that a 45 amp input limit is appropriate. And those who would be tempted to simply shift up to a 4S setup without appropriately reducing the propeller size will probably have trouble.

Happy Landings,

Don
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Old Dec 15, 2014, 08:58 PM
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Thanks very much Don, that makes sense and that is pretty good at 4s for a $30 motor.

What are you planning to run it on, on 3s if you don't mind me asking and what size prop? My bench tests show 15x6 to 15x8 Aeronaut to be in the 45a ballpark on 3s.

I am flying full house 3m Polecat Skydancer 59oz , on Hyperion GS3020-12 , 782kv on 3s1300 45-90C nanotech, with 15x6 Aeronaut at 35A 380W in, do not know what efficiency , I assume quite under 70% , but even at that I get consistent 26 sec to 200m ( according to my RAM unit) at about 70 deg angle and can range out quite a bit. If it starts blowing, I can go to 15x8 at 50A 520w input and improve my climb quite a bit but most of the time just don't need it.

I am just building 4m Euphoria F5J from Ukraine and this motor would fit tight but it would work but I also have Hyperion Z3025-08 985kv that also fits and is better quality, I think that I may go with instead, will try that one at 3s and 4s , and maybe come back to this one if not quite satisfied, depends what my final weight will be. It seems the high watts are not always needed as long as you have some headroom in your climb for ranging out.

Dan


Dan
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Old Yesterday, 10:37 AM
Flying = Falling (Slowly)
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Tulsa, OK
Joined May 2004
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Quote:
Originally Posted by ddruck View Post
Thanks very much Don, that makes sense and that is pretty good at 4s for a $30 motor.

What are you planning to run it on, on 3s if you don't mind me asking and what size prop? My bench tests show 15x6 to 15x8 Aeronaut to be in the 45a ballpark on 3s.

I am flying full house 3m Polecat Skydancer 59oz , on Hyperion GS3020-12 , 782kv on 3s1300 45-90C nanotech, with 15x6 Aeronaut at 35A 380W in, do not know what efficiency , I assume quite under 70% , but even at that I get consistent 26 sec to 200m ( according to my RAM unit) at about 70 deg angle and can range out quite a bit. If it starts blowing, I can go to 15x8 at 50A 520w input and improve my climb quite a bit but most of the time just don't need it.

I am just building 4m Euphoria F5J from Ukraine and this motor would fit tight but it would work but I also have Hyperion Z3025-08 985kv that also fits and is better quality, I think that I may go with instead, will try that one at 3s and 4s , and maybe come back to this one if not quite satisfied, depends what my final weight will be. It seems the high watts are not always needed as long as you have some headroom in your climb for ranging out.

Dan


Dan
Dan,

Actually I am planning to use the MVVS 4.6/840. I ran some preliminary tests with a 15x10 and it seemed to work well at around 40 amps. I will be doing more testing before too long.

Remember, the MVVS is not exactly the same as the GliderDrive and will probably take a slight larger prop than the MVVS.

Happy Landings,

Don
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