Variable pitch quadcopter - RC Groups
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Nov 03, 2017, 12:25 AM
Registered User
Build Log

Variable pitch quadcopter


Hi guys!

I just started to build a variable pitch quad and wondering if i can configure Betaflight running on a SPracingF3 to handle this setup.

As far as i understand how it works it would be sufficient to set motor outputs to legacy PWM, separate PWM from PID loop, set PWM rate to 330 Hz, set the throttle values according to the desired servo travel and pass one auxiliary rc channel to the ESCs.

Is this correct or do i have to reassign the outputs and mess around with custom mixers or choose a different flight controller?

I would appreciate any hint very much.
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Nov 03, 2017, 01:56 PM
Registered User
géry 46's Avatar
nice concept..very interesting...
Nov 04, 2017, 01:13 PM
Registered User
remember your more of a mechanical quad now, so there is more potential for failure with all those parts.

the biggest failure poin is the set screw that attaches the motor shaft to the collective, these always fail on rc helis, even with locktight. specifically around the pinion gears to shaft coupling, a redesign is smart if your adding $$$ gear and relying on those tiny set screws to hold together
Last edited by moonraker007; Nov 04, 2017 at 01:18 PM.
Nov 04, 2017, 03:56 PM
Registered User
Quote:
Originally Posted by moonraker007
remember your more of a mechanical quad now, so there is more potential for failure with all those parts.

the biggest failure poin is the set screw that attaches the motor shaft to the collective, these always fail on rc helis, even with locktight. specifically around the pinion gears to shaft coupling, a redesign is smart if your adding $$$ gear and relying on those tiny set screws to hold together
Yeah, you are absolutely right! Thanks a lot i will check the couplings twice before starting the first tests,

If this prototype works well i will look for someone to make custom motor axles so there will be no more coupling except inside the motors.

For now final sprint has begun. I just have to change the motor axles before i can start to assemble arm no 3+4.
Nov 05, 2017, 01:51 PM
Registered User
yeah i would redesign it , with a jesus bold instead of setscrews. it's hard to drill motor shafts, you will need to order carbide drill bits and run them at the correct rpm when cutting.
Nov 05, 2017, 02:11 PM
Hamburger
hamburger's Avatar
from photos it is unclear what size you build.
Several years ago someone mentioned the heli tail units of the smaller helis come without thrust bearings (as would be normal in the main rotor hub) and it sounded like you definitely wanted those in.

Interesting to see 4 direct drive motors. The stingray uses one main central motor and belts to drive the props (the same as with helis).
Good luck.
Nov 05, 2017, 10:31 PM
Registered User
Quote:
Originally Posted by hamburger
from photos it is unclear what size you build.
Several years ago someone mentioned the heli tail units of the smaller helis come without thrust bearings (as would be normal in the main rotor hub) and it sounded like you definitely wanted those in.

Interesting to see 4 direct drive motors. The stingray uses one main central motor and belts to drive the props (the same as with helis).
Good luck.
Thanks!

The tail rotor assemblies used are of a 450 sized heli so no thrust bearings inside just ordinary ball bearings. In a future version (if this prototype works well) one option would be motor shaft and tail rotor shaft one solid piece. Another option would be to insert a free wheeling so the quad is still under control if motors or ESCs fail.

But first bring it into the air and let’s see what happens.

The blades i will use during the first tests are 210 sized CFK blades 13g each pair and optimized for high thrust per Watt. The second step will be to put on 3d capable blades and check out limits and weak points.
Nov 07, 2017, 02:19 PM
Design and fly
skycam4's Avatar
I built this unit several years ago. I used a single engine only because we built a gas version also. We're a few weeks away from a full size version I hope to be flying soon.

Something to inspire you.
Collective Pitch T-Copter Onboard video (2 min 37 sec)
Nov 09, 2017, 10:52 AM
Registered User
Quote:
Originally Posted by skycam4
I built this unit several years ago. I used a single engine only because we built a gas version also. We're a few weeks away from a full size version I hope to be flying soon.

Something to inspire you. https://www.youtube.com/watch?v=c2UVr08yaHw
Nice build thanks a lot for sharing.

My 3D Printer stooped working last night the NTC is gone so i have to wait for replacement parts before i can continue.
Nov 09, 2017, 11:24 AM
Hamburger
hamburger's Avatar
Quote:
Originally Posted by skycam4
I built this unit several years ago. I used a single engine only because we built a gas version also. We're a few weeks away from a full size version I hope to be flying soon.
rl]
You mran man carrying?
Nov 12, 2017, 10:53 AM
Registered User
Scratchbuildrc's Avatar
Reserved
Nov 12, 2017, 12:18 PM
Registered User
DenRotor's Avatar
Hi Woga65,

Looks like you are taking it to the next level. Sweet looking build!

I remembered this from a few years ago.

Curtis Youngblood's Stingray 500 3D quad.

Stingray 500 3D Quad copter from Curtis Youngblood (2 min 56 sec)
Nov 12, 2017, 08:09 PM
Registered User
Quote:
Originally Posted by DenRotor
Hi Woga65,

Looks like you are taking it to the next level. Sweet looking build!

I remembered this from a few years ago.

Curtis Youngblood's Stingray 500 3D quad.

https://www.youtube.com/watch?v=keG_5IkJKJE
Thank you! For now i would be glad to bring it into the air...

My printer is again up and running and the body of the drone is just finished. Arm no 3+4 are finished too and half of the soldering is done so i will do first tests most likely this week.

Yeah the Stingray is a very nice little machine and usually i like belt drives very much because in the case of a crash they keep damage away from motor and main gears but i know some people who own a Stingray an they say it‘s fine but it is fragile.

So i decided to go with lightweight low KV motors and direct drive.

New pics coming soon...
Nov 13, 2017, 08:33 PM
Registered User
Today i did first tests. After switching to (legacy) PWM, separating PWM from PID and setting it to 330 Hz Betaflight accepted the servos as if it were Esc.

Nevertheless i will have to setup a custom mixer to be able to config proper servo travels. For did a rough adjustment via the position of the ball links.

Unfortunately i missed to buy a proper BEC. Whenever i do rapid pitch changes the FC goes into a kind of fail condition and i have to disarm and rearm or do a power cycle to continue. Most likely the small BEC i had lying around is not able to supply four servos, FC and RX with stable power.

Additional one of the rotor shafts is not perfect straight and needs to be replaced. I guess that happend as the rotor touched a cup standing on my workbench.

For tomorrow i plan to clean up my quick and dirty build do some tests using the Esc to control the quad and the servos to preselect pitch values to find a proper combination of rotor diameter and LiPo cell count.

As soon as the new BEC arrives i will continue with the pitch control thing...

[Edit]Shaft replaced - pitch slider slides slidy again! [/Edit]
Last edited by Woga65; Nov 13, 2017 at 09:45 PM. Reason: Completion
Today, 11:20 AM
Registered User
Hi all!

Today i had some free time and manged to clean up my first messy design of the body.

The new body is more old school and service friendly.

Stiffer - lighter - better! Or in the words of a well known B. Willis movie: Older - harder - better!

Old design:

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New design:

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