coax prop pitch selection

[Danub]

OK guys I have been trying to wrap my mind around this one.
With coaxial setups ie: y6 or x8 (btw what is xy8?, i don't get that one)
What is the deal with prop pitch?
Some guys use the same ones top and bottom? Why?
Some guys use a deeper pitch on the lower motors? Why?
I heard one theory that you can go with a little larger prop (15%) on the bottom and keep the same pitch?

The reason I ask is my 1st coaxial setup on multiwii FC flew like crap. It always yaws clockwise in forward flight, Can't figure it out
I am thinking about changing my uap1 to a Y6 and am trying to avoid the same challenge. (uap1 is on NAZA)

Please hit me with your theories/thoughts

 

[Bartman]

OK guys I have been trying to wrap my mind around this one.
With coaxial setups ie: y6 or x8 (btw what is xy8?, i don't get that one)
What is the deal with prop pitch?
Some guys use the same ones top and bottom? Why?
Some guys use a deeper pitch on the lower motors? Why?
I heard one theory that you can go with a little larger prop (15%) on the bottom and keep the same pitch?

The reason I ask is my 1st coaxial setup on multiwii FC flew like crap. It always yaws clockwise in forward flight, Can't figure it out
I am thinking about changing my uap1 to a Y6 and am trying to avoid the same challenge. (uap1 is on NAZA)

Please hit me with your theories/thoughts

Hi Danub,

THe theory is that the airflow coming from the top props causes the lower props to perform as if they have lower pitch. to correct this the lower props need to have higher pitch so they'll perform more like the top props.

the XY8 is a coaxial quad with more space across the front and rear motors than between the side motors. it's a compact format that I came up with to get a clear forward view for shooting photos and video while also having eight motors like a regular x or + coaxial quad.

Bart

 

[Danub]

OK I get what you are saying partially.
Can I "overprop" the lower motors?

Example I want to try:
Avrotos on 4S. . . Y6 configuration around 3-3.5kg.
I am considering trying these props:
11x5 xoar pja props on the upper motors
11x7 xoar pja-p props on the lower motors. E-calc has me at a little bit over max motor limit by like 15Watts? Maybe apc's while I wait for the xoars.
I was hoping to go 12x5/7 combo but e-calc had a fit when I told it I wanted the weight of a second battery?? 12x7 says 459 watts? but that is the lower motor with lighter load soooo it should be less??

I am a tad bit confused how to handle the coax prop evaluation part and insight would be awesome as i just tore my hex apart and by tomorrow it will be a Y6.

 

[Bartman]

11x5 on top and 11x7 on the bottom will be an ok place to start. at the weight you're talking about you might have too much prop, you can always give 10" props a try if the 11's are too floaty or don't give very good flight times.

bart

 

[Subzero_1]

Hi Bart,
I too have similar problem with coax prop setup.
On flat octo, Wkm, Graupner 11x5 were rock steady, but now what to start with on coax?
I have APC 14"x4,7 slow fly, to put on top. Question is what to use on lower motors?
13"x6,5 but they are not slow fly, they are thin electrics. Can one mix them?
Is it true that wkm coax "likes" shorter booms?

Oliver

 

[helloman1976]

OK guys I have been trying to wrap my mind around this one.
With coaxial setups ie: y6 or x8 (btw what is xy8?, i don't get that one)
What is the deal with prop pitch?
Some guys use the same ones top and bottom? Why?
Some guys use a deeper pitch on the lower motors? Why?
I heard one theory that you can go with a little larger prop (15%) on the bottom and keep the same pitch?

The reason I ask is my 1st coaxial setup on multiwii FC flew like crap. It always yaws clockwise in forward flight, Can't figure it out
I am thinking about changing my uap1 to a Y6 and am trying to avoid the same challenge. (uap1 is on NAZA)

Please hit me with your theories/thoughts

I've had a Y6 before and used 10x5 APC props on it and I noted that when i'd YAW i'd lose altitude which is a common problem with coax setups because they are not as efficient as a flat Hexa design. The reason is because the airflow below the first prop is turbulent and the lower props have a harder time biting into it. The theory behind the deeper pitch is that it helps to solve this issue with a deeper pitch that can bite into the more turbulent air a little better. If you put larger props on the bottom you are just biting into a larger surface area and an area outside of the turbulent air being create so the principle is similar. Check out what the Army did with it's pusher-puller airplanes in Vietnam, like the O-2 Skymaster, to get some ideas on how to cure this issue. It's similar to the problem helicopters have with rotor wash when they get close to the ground and they lose efficiency or the flip-side of it whereas the helicopter will become more efficient in forward flight because it's able to bite into air that has not been disturbed by rotor wash, i.e. the air in front of it.

 

[tahoelight]

This may be a coax prop question, or it may not. I fly Hoverfly Pro on a Coax xy8 and x8. Both with avroto 2814 on 4s. I have tried xoar 12x6 top and bottom, 12x6 top/13x7 bottom and the best results seems to be 12x6 xoar top and 13x6.5 APC e-prop bottom. I get perfect 50% throttle but gains are really low. To the point where there is no room between oscillation and sloppy flight.

Has anyone flying a coax with 2814 motors with Hoverfly Pro find gains need to be really low, otherwise there is bad oscillation? Any suggestions?

 

[helloman1976]

This may be a coax prop question, or it may not. I fly Hoverfly Pro on a Coax xy8 and x8. Both with avroto 2814 on 4s. I have tried xoar 12x6 top and bottom, 12x6 top/13x7 bottom and the best results seems to be 12x6 xoar top and 13x6.5 APC e-prop bottom. I get perfect 50% throttle but gains are really low. To the point where there is no room between oscillation and sloppy flight.

Has anyone flying a coax with 2814 motors with Hoverfly Pro find gains need to be really low, otherwise there is bad oscillation? Any suggestions?

I don't and haven't flow either but I recently switched over back to the Y6 design using Rusty's UAP-2 setup. I'm currently using 11x5 carbon fiber props on both the top and the bottom. I'd say, make sure your props are balanced as perfectly as possible. What flight controller are you using? When you say 50% throttle this is done in manual mode right? Have you tried a range of tuning values? Sometimes going to too low is WAY too low and to get smoother flight you need to bump up those values quite a bit. For example, if at value 60 you get sloppy flight but at value 65 you get smoother flight and then 75 you can sloppy flight again it may be because you should really be at 135 and you are too way too low to start tuning. I've seen this before with Naza flight controllers which is what I use as well as KK boards, don't use those. It can look like things got slight better and then a higher value makes them look worse again and you're thinking that you went too high when in fact you're way off and need to be much, much higher before you start tuning.

The speed of your motors and the weight of your craft as well as the balance of the crafts weight to center of gravity will have heavy impacts on tuning. Optimally you want everything at the center of gravity including your flight controller but that's not always possible so make sure everything is as balanced as possible.

Also consider that a failing motor, bad connection/s or ESC can result in glitching and it's not actually a tuning problem. Hope that helps...

 

[jfro]

This may be a coax prop question, or it may not. I fly Hoverfly Pro on a Coax xy8 and x8. Both with avroto 2814 on 4s. I have tried xoar 12x6 top and bottom, 12x6 top/13x7 bottom and the best results seems to be 12x6 xoar top and 13x6.5 APC e-prop bottom. I get perfect 50% throttle but gains are really low. To the point where there is no room between oscillation and sloppy flight.

Has anyone flying a coax with 2814 motors with Hoverfly Pro find gains need to be really low, otherwise there is bad oscillation? Any suggestions?

With the 12x6 and 13x6.5 props, what are your batteries, total weight, and flying time.

I'm flying x8 with avroto's and getting very short flying time with 11x4.7's and 5000 mAh 4s/ 30-40c batteries, weight about 12lbs. Going to try your 12-13 combo and see if that helps.....

 

[Dewster]

I have a 7 pound Y6 with Avroto Motors and was using 11x5 Graupner props top and bottom. My craft would always slowly descend out of altitude at 50 percent throttle. The only gain adjustments that I made were for control movement to smooth out transitions. I purchased 12x6 Graupner props for the bottom of my craft and now its rock solid. It holds altitude right at 50 percent throttle. A hair above or below the fifty percent mark and it will climb or descend.

You can barely see the length difference of the props. You wouldn't see unless I told you that the props were different. The increased length and pitch helped to keep my craft where I put it in flight.

With the Sony Action camera, two 3s 6000 mah lipos I get 6.5 to 7 minutes of flight time. I have to adjust the voltage monitor to get better use out of the batteries.... Wish my craft was lighter.... Is extremely quiet at altitude.

 

[Stacky]

Tahoe, I have a X8 with similar size motors and 12x3.8 apc props on top and 12x6 apc electric thins on the bottom. My gain settings for my HFP X8 are virtually the same as for my Hexa and both the Hexa and X8 have virtually the same motor to motor distance of 750mm. Both machines weigh in at 4kg. My gain settings for both machines are about 40. I did have a problem with "surging" power at one point when using cheap RCTimer motors that are the same size as my Sunnysky 2814's and that turned out to be badly balanced motors. I know Avrotos are well balanced but it might be worth having a peek at that with a vibration meter app on your cellphone if possible?. Just a thought, you might have one motor with an out of balance prop adapter?.

This may be a coax prop question, or it may not. I fly Hoverfly Pro on a Coax xy8 and x8. Both with avroto 2814 on 4s. I have tried xoar 12x6 top and bottom, 12x6 top/13x7 bottom and the best results seems to be 12x6 xoar top and 13x6.5 APC e-prop bottom. I get perfect 50% throttle but gains are really low. To the point where there is no room between oscillation and sloppy flight.

Has anyone flying a coax with 2814 motors with Hoverfly Pro find gains need to be really low, otherwise there is bad oscillation? Any suggestions?

 

[clevis41]

x8 450 custom

View attachment 19084

I have a 7 pound Y6 with Avroto Motors and was using 11x5 Graupner props top and bottom. My craft would always slowly descend out of altitude at 50 percent throttle. The only gain adjustments that I made were for control movement to smooth out transitions. I purchased 12x6 Graupner props for the bottom of my craft and now its rock solid. It holds altitude right at 50 percent throttle. A hair above or below the fifty percent mark and it will climb or descend.

You can barely see the length difference of the props. You wouldn't see unless I told you that the props were different. The increased length and pitch helped to keep my craft where I put it in flight.

With the Sony Action camera, two 3s 6000 mah lipos I get 6.5 to 7 minutes of flight time. I have to adjust the voltage monitor to get better use out of the batteries.... Wish my craft was lighter.... Is extremely quiet at altitude.

hi guys, i just started flying a custom x8 that i built . im reading all about how you are using different props on bottom than the top. hmmmmm thats interesting . i have all the same at the moment . 11x4.5 apc MR props. craft weigh around the 3000 gram or say 7lbs it does hover good but it does wobble at times a bit . im wondering if changing bottom props would be the solution. running duel 3s

 

[Dewster]

I used 11 inch props on top and 12 inch props on the bottom of my Y6. It took some experimentation, but my different prop set up kept my craft steady and also prevented unwanted yaw.