Hey guys and gals!  I've been getting into some long range (technically really short long range atm) and trying to figure out a good balance between prop size for 7 inch and motor sizes.

My first 7 inch build had it's first test flight today, I found it a bit underpowered on 4s.  It's running racerstar/t-motor collab motors, the 2508 size at 1200kv.  This is quite large I know for 7 inch.

I found it ran really well on my CNHL 6s 1000mah pack but flew ok on 4S.  I've bought another 6s pack to try it out on that.

What I was curious on is motor size.   What size motors can you get away with on a 7 inch?

I was thinking of the following combination on another 7 inch frame that is more 4s orientated.

The motor is the ethix 2306 sized 2345kv motor, I would like to try this on a 7 inch frame, would this motor be able to handle this load?

Thoughts are appreciated.

cheers,

ph2t.

I started looking at motors for my 7" after finding that the higher KV motors are just not efficient enough for long ranges. 2300-2500kv motors provide awesome performance and allow for use of 4S, but neither of those things are conducive to true range. When I realized that 2207-2400kv motors were wholly wrong for what I was after, I shifted to 2305-1900kv motors and found a sort of happy place...though far from perfect.

When the search for motors started up again, 1700-1900kv motors in 24xx and 25xx seemed to be making some of the best strides. A 1900kv will fly well combined with 4S and can also be combined with 6S if you want to take it up a notch. A 2306-1900kv motor should be a good choice, but 23xx is the smallest motor I would opt for as turning a 7" prop is a lot of work and smaller motors have to work too hard.

Hope this makes some sense. I am just trying to get out the door for work

(24-Dec-2019, 03:18 PM)kaitylynn Wrote:    A 2306-1900kv motor should be a good choice, but 23xx is the smallest motor I would opt for as turning a 7" prop is a lot of work and smaller motors have to work too hard.

 

I agree with Kaity, 23XX is as small as I think you should go.  And frankly going with 25XX is fine.  Most of the long range guys with 7" blades go with a 25XX motor.  

But to directly answer your question, yes those motors will handle the load.

https://brotherhobby.com/avenger-2810-mo...172p1.html
https://brotherhobby.com/avenger-28065-m...132p1.html
i guess 28xx size would be good choice to get sure about „underpowered“, i beleive they should be well about efficiency aswell, not sure about. the 2806,5 draw 4,6a while 530g thrust per motor 40%throttle data.

Thanks everyone! Really appreciate the advice.

Cheers,

ph2t.

So I have now mounted the 2306 sized motors onto a clone frame from banggood.   I made a mistake though in the motor selection.  I'm actually using the RR hypetrain drib motors.

EDIT: sorry this post got edited and the attachments got mangled.  I have uploaded the attachments again and then lost some txt I posted.

Since this post is in a long range section, I'm guessing you will be going out some distance.  A couple things, a 2600kv motor isn't the best for LR, but not the end of the world.  My 6 inch Rooter has 2600 motors and I can get around 3 miles out with it, with 5 inch blades.  But my battery is much bigger, at 2200mah, and I keep my amp draw below 10 amps during flight.  So if you are going to keep your flights in around a mile or so the battery size you mention will probably be fine with a light throttle finger.  If you haven't bought the batts yet, and don't want up to 2200 size, maybe try 1800mah.  More battery is more flight time.

I see a bigger problem though.  Given you were kind of at the limit with smaller motors for 7 inch blades, and then went up on kv, you are now in a danger zone for motor heating, needing an esc rating of 60+, and needing a high C rated battery.  These findings are based on what ecalc is saying.  Since ecalc doesn't have the 
Le Drib motors in its list of motors, I had to plug in similar, so the results aren't perfect but likely close.  

When you maiden the quad I would take extra time flying short flights and gradually increase load between flights.  Landing and checking esc, motor and battery temps frequently.  

Also keep the pitch low on the blades to start, no higher than 4 inch pitch and preferably 3 inch to start.  As you slowly check things out you can go up on pitch to see if the system can handle it.

Clearly if you baby the quad it will be fine.  It's when you start to push it, you may find you have some weaknesses.

Thanks for posting your build photos.  Nice build!

Throttle Expo...I had to adjust mine so that I had some smoother throttle response across the sticks travel as the 7" can be a bit "torquey". I found myself flying only the bottom 1/3rd of the stick almost exclusively, so I added some negative curve. It is one of the smoothest flyers I have now.

Also, check your prop hubs EVERY FLIGHT. I have had a few of the HQProps catastrophically fail during flight due to blades separating. Could be that I habitually over-tighten the prop nut...but it has only ever happened with the 7". The issues I had with the GF's, jello...I mean JELLLLLLOOOOO. It would almost make me motion sick while flying.

Thank you guys! I really appreciate the advice.

I have two projects now - pure play long range model - Gep 7" croc frame with 2508 motors on 1200kv, it's underpowered on 4S, runs well on 6S. I just got a new Bonka 6S 1800mAh pack which I'm going to try out tomorrow. I found the croc works best on 6s - right in line with your advice guys thanks!

The other project, this one using the 2306 motors is now becoming more a freestyle frame, or that is my intentions. I am going with the biblades first, thank you for the information there on the pitch of the props and its contribution to the load on the motor and power plant.

I'm finding the foray into 7 inch quads really interesting. There's a lot going on in this class!

cheers,

ph2t,

(30-Dec-2019, 02:32 PM)ph2t Wrote: Thank you guys! I really appreciate the advice.

I have two projects now - pure play long range model - Gep 7" croc frame with 2508 motors on 1200kv, it's underpowered on 4S, runs well on 6S.  I just got a new Bonka 6S 1800mAh pack which I'm going to try out tomorrow.  I found the croc works best on 6s - right in line with your advice guys thanks!

The other project, this one using the 2306 motors is now becoming more a freestyle frame, or that is my intentions.  I am going with the biblades first, thank you for the information there on the pitch of the props and its contribution to the load on the motor and power plant.

I'm finding the foray into 7 inch quads really interesting.  There's a lot going on in this class!

cheers,

ph2t,

Also, the info I mentioned above with with 6s, as I seem to remember that is what the platform was going to be.  If you put in 4s into the system the problems drop off significantly.  Just food for thought.

Here are some more build pics of the freestyle project.

It's a clone of the slamnasty I believe - it does not have the raised rear arms though as the original does.  It was cheap like me.   



Specs:

Aikon F4 FC
Airbot Furling32 45A Blheli32 4in1 ESC
Drib motors, 2650kv size: 2306
Crossfire nano rx with an immortal T antenna in a horizontal orientation
TBS unify HV race vtx
Foxeer Predator V2 (I think)
AXII MMCX RHCP antenna
HQPROP 7040 biblade propellers

There is not much room in this frame - the 30x30 stack takes up a lot of the bottom plate real estate.  I mounted the power filtering/spike capacitor against an arm.  In hindsight I should of placed it on the rear side of the up for more protection during forward movement.  It's a bottom mount lipo setup, never done one before.  Was cool to mount the XT60 downwards for once, lol.




Here it is with the bi-blades mounted ready for its maiden tomorrow morning.   



It's quite large against my rooster.



Packs are charging......  

ph2t.

Flight controller is running BF 4.1.2 with RPM filtering enabled.
DSHOT300 with 4k/4k PID loop results in AVG CPU of 11%.
PID values are defaults for 4.1.2
Filters are defaults for RPM filtering mode.

My rates
rc rate 0.8 all axis
super rate 0.6 all axis
rc expo 0.25 all axis
throttle mid 0.3
throttle expo 0.4

I've built up the rates values over time and they suit me well. We shall see how we go!

Cheers,

ph2t.

Nice clean builds!

Now we need to see in-flight video. 

I'm sure you know about horizontal only antennas for distance flying, not the best plan.

„Clearly if you baby the quad it will be fine“ like krohsis wrote; limit the motor_output of the 2600kv motors, scale to less kv would prevent befor waisting energy, high ampdraw... next to the throttle expo kaity wrote.

Thanks everyone for the words of encouragement.   

Krohsis, just want to say thankyou mate, I appreciate your advice with the focus on long range and I understand that the orientation of the crossfire antenna system needs to be vertical for the best long range performance.  You'd hate me, I got the microTX version and haven't done the mod to my QX7 yet for the better baud rate so I'm running it slow, lol!

Taking on your advice from many threads I've scoured in the 7 inch sub forum I have built a dedicated long range frame.  It's based on the GEPRC crocodile and has 2508 sized 1200kv motors on it.  What you and kaity said were spot on, 4S feels underpowered and 6S works well.  I just recently got the 1800mAh 6S bonka pack and that is a sweet spot for weight and performance.  I will post more on that in another thread on that build hopefully soon.

This thread is sorta now about the freestyle type 7inch build.  I know it's not sport on for the long range subforum as it started about a question for motor sizes to run 7 inch props well and took a turn from there : I guess the 7 inch prop is known for long range and hence putting the OP here.   Now with two 7inch projects going on I feel like the freestyle 7 inch project using the said 2306 sized motors being discussed is the main focus of this thread. 

Sorry to de-rail - inspiration and an eureka moment coupled with a general impatience to just use what I have lying around to cobble together an idea ends up with a thread like this.

So the bring it back to the original point.  

Motor sizes and power plants when driving 7 inch props

• ideal min motor size - 2306
  
• more common motor size - 25xx
  
• 1200kv - 1800kv on 6S has better chance of being efficient
  
• > 1800kv on 6S too hot a setup
  
• > 2400kv on 4S too hot a setup
  
• Always start with bi-blades to limit risk of too hot a setup
  

I've managed to get some flight time and found the motors I'm using at 2650kv are too hot to drive 7 inch props.  The lipo's voltage sag under throttle for 7 inch biblade on these 2650kv motors.  

I'll post my findings with a video separately.

cheers and happy new years from down under.

ph2t,