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Old May 12, 2011, 05:10 PM
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Gas Monkey Vic
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Snohomish, WA
Joined Jan 2005
1,523 Posts
This is my go to 30CC electric set up.
Scorpion 4035-380
CC Phoenix ICE 100
XOAR 19x10 prop
CC BEC Pro
6S 5000mah pack

CC ICE log
Watts: 2698 (CC ICE logger is not accurate)
Amps: 123 (CC ICE logger is not accurate)
RPM: 6950 (Hobbico tach)

Amp meter
Watts: 2024
Amps: 92
Rpm: 6950 (Hobbico tach)

My amp meter numbers line up with Joe’s test data (see pic)

My short answer on this set up.
I have run several 30cc sized planes with this exact set up and some are a few year old, i.e. My Sick V1 and now Slick V2 on the same old set up with 300+ flights with no issues. The max temp was in the summer and the motor was 165F.

The long and technical answer on the Scorpion 4035-380 with a Xoar 19x10 prop on 6S 5000mah set up from a brushless motor engineers stand point:
Quote:
When running on 6 cells, you should not run a prop larger than a 17x10 or an 18x8 on this motor. This is a very common mistake that people make when propping an electric motor. They figure that they spend the majority of their time flying at half throttle, where the motor only pulls 45 to 50 amps, so they should be fine even though the motor pulls over 90 amps at full throttle. Unfortunately this is not the case. Another mistake that people make is that a motor may be rated for 70 amps and 2400 watts, so they figure that if they are at 90 amps but only 2000 watts they are OK. Again, this is not the case, you cannot exceed either of these ratings on a motor. If you run the motor on 8 cells, you will hit the max power rating before you hit the max current rating, and this would be the determining factor.

The way that the ESC’s work is that the full battery voltage is applied to the motor during every pulse cycle. This means that the full 92 amps of current is present all the time. The ESC switches this power on and off 8000 times per second to vary the power level to the motor. When you are running at half throttle, you get 92 amps of current for a few micro seconds, then 0 amps for a few micro seconds, followed by 92 amps for a few micro seconds and so on. When you hook a watt meter to the set-up, it averages out these pulses and will show a current of 45 amps, but in actuality, the motor is getting hammered with 92 amp current pulses at the rate of 8000 times per second. This happens the entire time the motor is running at a steady throttle setting.

Unfortunately, whenever you transition from idle to full throttle quickly, it take about 1 to 1-1/2 seconds for the prop to completely accelerate to full throttle. During this time period, the current actually goes up past the 92 amp steady state, and can go as high as 150 amps or more when you open the throttle, and then drop back to 92 amps as the motor reaches full speed. This situation is exceptionally hard on the motor, especially if the motor momentarily loses sync with the speed controller. When this happens, you will often hear a screeching noise from the motor or a clicking noise that sounds like you are throwing stones into the propeller while the motor is running. Either of these situations can wreak havoc on the magnets, and can actually tear them loose from the glue that they are attached to.

This is why it is imperative that the maximum current rating of a motor never be exceeded under any circumstances. If you keep the maximum current rating of the motor within the recommended value, there is enough leeway to allow for the extra current that is present during motor acceleration. However, when you load the motor down way over the recommended maximum current, it will eventually destroy the motor.
From a brushless motor engineers stand point we are all over propping but we all say “the manufactures specs are way under rated” How many times have you read that statement?

I think and hope the Scorpion 4035-380 motor I bought last July and have 40 to 50 flights on in the EG Slick and MXS just had a manufacturing defect. Like others have said I feel heat is letting you know your pushing the system and I do not think 165F motor temp in the summer is pushing it.

Chris,

I would say your right on track with 6 cells a 400-450 gram 380kv motor with a 18"-19" prop is the best overall setup for the Slick. I think any of the motors you are looking out will be just fine. Many out there are using them and are happy with them.

I would like to try out the Motrofly 4325-380.
19x10 APC, 22.1V, 6125 rpm, 83.77 amps, 17.5 lbs.
That is lower amps and higher rpm then my Scorpion. 17.5lbs of thrust in a 9.3lb plane sounds good to me.

Happy motor selecting,
Vitter
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Last edited by Vitter; May 12, 2011 at 05:16 PM.
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