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Propller choise for contra drive, test with Twin-Motor contra system.

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Propller choise for contra drive, test with Twin-Motor contra system.

Old 09-17-2020, 05:16 PM
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Mark Hu
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Default Propller choise for contra drive, test with Twin-Motor contra system.

Most F3A fliers use props as drive makers recommend, like 22X20F and 22X22R, I use this for 3 months with my first self made contra drive, and they recommend that the rear prop should be bigger pitch than the front. I want to try new props, 23 inches, but I'm not quite sure about the pitch choice.
Recently I build a series of contra drive system for my F3A, one of the most interesting drives is a Twin-motor contra drive, with 2 ESC, that is just a perfect project for my prop test. I just finished a lot of test flight yesterday with different props, got current and RPM data from all different props combinations.
I have BJ craft agenda CD, 4600mah 10S batteries, 4.8kg take-off weight. Banner‘s props 22X20F and 22X20R, Falcon 22X22F,22X20F, and 22X22R. I have one ESC with telemetry, I have 2 completely independent ESC~motor~prop drive train in my Twin-Motor contra drive system. With my Twin-motor contra drive, I can easily compare the working condition of 2 props, and I will have an idea to chose prop to make them balance.
Here is my test idea:
prepare:
  • Two 80A HV ESC calibrate range together. the ESC I used is a kind of fixed-parameter ESC, just calibrated the range, it will make tie 2 working the same way.
  • Number the motor, 1 and 2, 1 is the right motor, 2 is the left one.
  • Number the ESC 1 and 2, Number 1 ESC with telemetry.
Methods of test:
  1. No.1 ESC drives No.1 motor and drive the rear prop, fly with Full Charged batteries, do vertical climb 2times from 20M to 300M, (set 300m warning) take video from the transmitter screen, record the RPM and current for No.1 ESC when it is stable, landing, test the temperature of two motors.
  2. Switch the ESC and motor cable, No.1 ESC drives No.2 motor and drive the front prop, do the same vertical climb 2 times, take video and record the RPM and current from No.1 ESC when it is stable, landding, test the temperature of two motors.
  3. in consideration of the batteries voltage drop, switch back the ESC and motor cable and do step 1 again, record and landing, and test the temperature of two motors.
  4. in consideration of the motor difference, charge batteries and switch the gear to let the No.1 motor drive the front prop and No.2 motor to drive the rear prop. Repeat the step 1,2 and 3, record the data.
  5. Test the different prop combinations and record the data.
After 5 hours test flight with Peter and Filex, we got a lot of videos, just need to collating all data from the video and put them together. Thanks, Peter and Filex! I can't get all the test data without your help.
The Twin-motor contra drive works even better than my expectation, high efficiency, quiet and powerful.
Here is some Rough data with 22X20 F&R Banners contra props: 4600RPM and total 72A in a stable vertical climb.
I will have a two days competition this weekend and I will change back to my single motor contra drive. next week I will post the test result here.
It's time to put your idea here, what's your idea about the prop balance for a contra drive? should we need a different pitch for fixed contra like adverrun? what we should use for a free contra system like banner's V4 and Twin-motor contra system?
Some pictures of my contra drive and agenda CD.
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underdw (09-19-2020)
Old 09-17-2020, 05:18 PM
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Mark Hu
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I can't post any pictures because I need at least 10 posts T_T

Old 09-17-2020, 05:18 PM
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Mark Hu
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Sorry I will post pictures when I can.
Old 09-18-2020, 08:25 AM
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Adam F3A
 
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Hi,
I fly twin motor setup for few years now with double telemetry setup. I have a lots of similar data. I'm curious if your conclusions are close to mine.
Long story short: I believe we need front prop diameter larger than rear about 1-1.5 inch and pitch of the rear prop larger the same. It's important to minimise differences in weight of propellers.
Closest combination from popular props are 23x20F and 22x22R of 22x20R for example.
Other findings:
- At some point I made experiment with 3-blade 22x21F and 2-blade 22x21R. Power, rpm and torque balance was close to perfect, but gyro effect showed up again and I drop that way.
- In my drive prop selection depend on type of ESC used. With regular ESC you have different rpm per prop. With governor ESC rpm are the same and load on prop differ a lot if you use similar propeller F and R.
- Proper propeller selection help a lot with yaw effect
- Load distribution between propeller depends on speed and throttle stick position. There is no such things like perfect prop selection. There is always a compromise. With my best setup I have 5A on F and 15A on R prop on horizontal cruise. But in vertical or dive this is most balanced setup.
- if you use 22x20F and 22x22R on adverrun like drive, you will need a bit of left side thrust, because most of power is consumed by R propeller.

I will wait for your conclusions.

Best regards,
Adam
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Old 09-18-2020, 10:59 AM
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Adam, just out of curiosity, how much does your Twin-Motor Contra System weigh?
Old 09-18-2020, 03:03 PM
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Please keep this thread going, Mark and Adam. Most intriguing information from two guys who clearly know what they're doing. I've followed Adam for some time and his "data bank" is awesome but now I see another modeler with similar skills. I'll be following closely and thanks for the info.
Old 09-18-2020, 05:28 PM
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Mark Hu
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Originally Posted by Adam F3A View Post
Hi,
I fly twin motor setup for few years now with double telemetry setup. I have a lots of similar data. I'm curious if your conclusions are close to mine.
Long story short: I believe we need front prop diameter larger than rear about 1-1.5 inch and pitch of the rear prop larger the same. It's important to minimise differences in weight of propellers.
Closest combination from popular props are 23x20F and 22x22R of 22x20R for example.
Other findings:
- At some point I made experiment with 3-blade 22x21F and 2-blade 22x21R. Power, rpm and torque balance was close to perfect, but gyro effect showed up again and I drop that way.
- In my drive prop selection depend on type of ESC used. With regular ESC you have different rpm per prop. With governor ESC rpm are the same and load on prop differ a lot if you use similar propeller F and R.
- Proper propeller selection help a lot with yaw effect
- Load distribution between propeller depends on speed and throttle stick position. There is no such things like perfect prop selection. There is always a compromise. With my best setup I have 5A on F and 15A on R prop on horizontal cruise. But in vertical or dive this is most balanced setup.
- if you use 22x20F and 22x22R on adverrun like drive, you will need a bit of left side thrust, because most of power is consumed by R propeller.

I will wait for your conclusions.

Best regards,
Adam
Hi Adam,
Thanks for your reply,I read it in the first minute, but I can't reply you, I was limited by the system becaus I'm a new user, I have only 5 posts in every 24 hours, after 10 posts we can post pictures. I should post more^_^
I have only one sensor so I can only do the rough test like I planed before, but the test is enough for me to have a decision to change my current set up on my fixed contra drive. Like you say, I found that if I use same diameter but big rear pitch, the rear prop will take most of the load and I need a left thrust. Shake hands.
I only test one working point, Full throttle vertical climb, I think with fixed contra drive, we shoud use at least same diameter and pitch prop F&R, more balance then same diameter but rear biger pitch, I fly 22X22 F&R on my fixed contra yesterday, too windy to tell the difference, but I will keep this setup for a while.
Next week I will try to record the data from both esc and do more analyze.
Here is my idea for different contra drive type.
1. Banner's V4, free contra, the gearbox will balance the torque between two props, but RPM is not fixed ,if prop selection is not good, RPM difference become bigger, gyro effect show up, and motor fix to the fuselage ,the shaft drives the gearbox, the system runs just like a 30K RPM small motor drive a small prop, you still have a small torque to your fuselage, equal to the output torque of the motor. Not much but still there.
2. fixed contra, like adverrun, the gearbox fixed the RPM F&R, gyro effect will be limited by the gearbox, but load difference will be biger if the prop selection is not good. As you say, there is no such things like perfect prop selection, But we can still find the good one for F3A working condition.
3.Twin-motor contra, we have the choice. we can fix the RPM and it will perform like fixed contra, or we can use some control method to match the current between, current is torque for motor. With normal ESC, we can set different throttle curve. And we can desigh some special governor ESC for twin_motor contra. My idea is contral the RPM for master channel and match the current for slave within a limited RPM difference.
Thanks Adam, your reply makes this topic more and more interesting, current I just have the same conclusions as you, and I will do more test in the future, I 'm sure we could find more if we test more.

Best regards,

Mark

Last edited by Mark Hu; 09-18-2020 at 05:55 PM.
Old 09-19-2020, 03:38 AM
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Adam F3A
 
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You can see weight of drives I use on pictures (if they show up).
First on is my initial design. Second is an current prototype designed for use with classic propellers and spinners.
Weight is no issue, my first choice plane is Fantasista with first drive and I was measured 4750g at WC with 5100mAh Hacker battery.

Matching current double ESC is ready to use. Take a look at double VESC. But I don't like that idea. Systems with fixed rpm per propeller sounds in air much better in air. Especially direct drive

Best regards,
Adam
Old 09-19-2020, 03:41 AM
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Adam F3A
 
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I tried, but I'm not allowed to post pic. Maybe another time.
First motor is 672g on scale with spinner, no props. Second is 604g with no spinner, no props, with R prop nut.

Best regards,
Adam

Last edited by Adam F3A; 09-19-2020 at 03:46 AM.
Old 09-20-2020, 01:04 PM
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Mark Hu
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Originally Posted by Adam F3A View Post
I tried, but I'm not allowed to post pic. Maybe another time.
First motor is 672g on scale with spinner, no props. Second is 604g with no spinner, no props, with R prop nut.

Best regards,
Adam
We need more posts, over 10 we can post pictures. my one 550g with no spinner, no props, with R prop nut. small motors with gears.
Old 09-21-2020, 03:50 AM
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Adam F3A
 
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So, discussion will slow down, I think.
What motor did you found useful for your drive. What kv and gear ratio?
Old 09-21-2020, 05:38 AM
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Yes, more input. PM me if either of you want photos posted, I'll provide an email. Thx, Ted.
Old 09-21-2020, 07:05 AM
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Mark Hu
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Originally Posted by Adam F3A View Post
So, discussion will slow down, I think.
What motor did you found useful for your drive. What kv and gear ratio?
585kv 170g motor and gear ratio 1:4.4.
Old 09-21-2020, 07:13 AM
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Mark Hu
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I Just need 2 more post,this is one of them^_^
Old 09-21-2020, 07:44 AM
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Mark Hu
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Originally Posted by Mark Hu View Post
Most F3A fliers use props as drive makers recommend, like 22X20F and 22X22R, I use this for 3 months with my first self made contra drive, and they recommend that the rear prop should be bigger pitch than the front. I want to try new props, 23 inches, but I'm not quite sure about the pitch choice.
Recently I build a series of contra drive system for my F3A, one of the most interesting drives is a Twin-motor contra drive, with 2 ESC, that is just a perfect project for my prop test. I just finished a lot of test flight yesterday with different props, got current and RPM data from all different props combinations.
I have BJ craft agenda CD, 4600mah 10S batteries, 4.8kg take-off weight. Banner‘s props 22X20F and 22X20R, Falcon 22X22F,22X20F, and 22X22R. I have one ESC with telemetry, I have 2 completely independent ESC~motor~prop drive train in my Twin-Motor contra drive system. With my Twin-motor contra drive, I can easily compare the working condition of 2 props, and I will have an idea to chose prop to make them balance.
Here is my test idea:
prepare:
  • Two 80A HV ESC calibrate range together. the ESC I used is a kind of fixed-parameter ESC, just calibrated the range, it will make tie 2 working the same way.
  • Number the motor, 1 and 2, 1 is the right motor, 2 is the left one.
  • Number the ESC 1 and 2, Number 1 ESC with telemetry.
Methods of test:
  1. No.1 ESC drives No.1 motor and drive the rear prop, fly with Full Charged batteries, do vertical climb 2times from 20M to 300M, (set 300m warning) take video from the transmitter screen, record the RPM and current for No.1 ESC when it is stable, landing, test the temperature of two motors.
  2. Switch the ESC and motor cable, No.1 ESC drives No.2 motor and drive the front prop, do the same vertical climb 2 times, take video and record the RPM and current from No.1 ESC when it is stable, landding, test the temperature of two motors.
  3. in consideration of the batteries voltage drop, switch back the ESC and motor cable and do step 1 again, record and landing, and test the temperature of two motors.
  4. in consideration of the motor difference, charge batteries and switch the gear to let the No.1 motor drive the front prop and No.2 motor to drive the rear prop. Repeat the step 1,2 and 3, record the data.
  5. Test the different prop combinations and record the data.
After 5 hours test flight with Peter and Filex, we got a lot of videos, just need to collating all data from the video and put them together. Thanks, Peter and Filex! I can't get all the test data without your help.
The Twin-motor contra drive works even better than my expectation, high efficiency, quiet and powerful.
Here is some Rough data with 22X20 F&R Banners contra props: 4600RPM and total 72A in a stable vertical climb.
I will have a two days competition this weekend and I will change back to my single motor contra drive. next week I will post the test result here.
It's time to put your idea here, what's your idea about the prop balance for a contra drive? should we need a different pitch for fixed contra like adverrun? what we should use for a free contra system like banner's V4 and Twin-motor contra system?
Some pictures of my contra drive and agenda CD.
Finally, I can post pictures^_^






new contra only 478.5g

4600 Redzone 485.4g

new contra fit in

weighting

4463g with new contra drive. takeoff weight

weekend competition



my first contra, 630g

first contra fit in

3D printed install fixture.

3D printed nose fixture.
Old 09-21-2020, 09:25 AM
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Prior to your posting pix, I had already done a little research on the stats you mentioned and had looked at the Hi Model Sunnysky x3120 585kv III since the specs were about right but I had come to the conclusion that when you stated 10s batts, you must have split them for 5s to each motor. It appears from your pix, that's what you've done. I would imagine with the lower rpm and spiral gearing, you've managed to get the noise level pretty low. Nice work.
Old 09-21-2020, 11:17 AM
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Adam F3A
 
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kv 585 and 4.4:1 -> That's 585/4.4=133 kv on prop shaft. That's definitely 10s setup.
Old 09-21-2020, 01:21 PM
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Mark Hu
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Originally Posted by Adam F3A View Post
kv 585 and 4.4:1 -> That's 585/4.4=133 kv on prop shaft. That's definitely 10s setup.
Sure it is. The working condition for motor is changed, but they two working well in this conditions. maybe higher rpm will damage these small motors, for test it works well, lots of full power test, I get 52℃ when landing.
Old 09-21-2020, 01:56 PM
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Ok, understood...sort of. So, you've rewound the motors or are just pumping 10s into 5-6s rated stock motors? Sounds like I'm confused....because I am.
Old 09-21-2020, 02:47 PM
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Mark Hu
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Originally Posted by ted32776 View Post
Ok, understood...sort of. So, you've rewound the motors or are just pumping 10s into 5-6s rated stock motors? Sounds like I'm confused....because I am.
Pumping stock motors.
​​​Just for test, I don't want spend too much for test. current and power within the spec, if it works the first time, it will work for all my test. If it is a good design, change motor will be a easy thing.

Last edited by Mark Hu; 09-21-2020 at 02:51 PM.
Old 09-22-2020, 01:04 PM
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Adam F3A
 
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Ted, the point you missing is voltage is no real limit for motor. Real limit is current and heat generated by this current. If you choose 40A motor you will get 800W motor at 20V and 1600W motor at 40V.
Of course, second motor will work at double rpm. You can try indoor motor at 10s, until high rpm will not destroy it.

Old 09-22-2020, 03:21 PM
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Thanks, a lot to learn for sure. Much simpler when all I had to concern myself was oil and nitro mixes.

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