Comment by Todd Hill on March 13, 2012 at 7:39pm

Have you tried moving the servo ball link closer to the servo horn screw. i know mechanically that will take some travel out. can you provide more information about your hardware?

Comment by Al Ros on March 13, 2012 at 8:00pm

Hardware is really simple

home made tri - frame sandwiched using PCB.

motors are park 370 hollow shaft - http://www.e-fliterc.com/Products/Default.aspx?ProdID=EFLM1210HS

e-flight variable pitch kit http://www.e-fliterc.com/Products/Default.aspx?ProdID=EFLPVPP100.

Pitch servos are hitech high speed digital tail servos - HSG-5084MG (unfortuantely non programmable)

Agree regarding servo horn. If I move control rod to toward the centre I can reduce travel. My problem is my scratch build servo base needs some work to allow the servo to more closer to the centre of the motor shaft.

Al

Developer Comment by Randy on March 13, 2012 at 9:19pm

Very impressive.  I'm slightly delighted and amazed that you got it working as well as you did without modifying the firmware.

Presumably the engine speed is controlled directly from a switch on the transmitter so it always spins at the same speed or is the channel 3 throttle sent to the engines as well as the APM?

BTW the Rate P is not used for the trad heli so that shouldn't make things better or worse.  Reducing your stabilize roll and pitch Ps until it stops wobbling should help.

For the yaw control do you have external gyro check on or off?

 

Comment by Al Ros on March 13, 2012 at 10:15pm

Hi Randy

Thanks for the tip on rate p and your interest in this.

I have set it up so that throttle goes directly to a 3 way divider cable and then to the speed controllers. I then set a throttle curve in the radio to allow the motors to shut down at zero throttle (for safety) and to ramp up to the desired speed fairly quickly.I have yaw currently controlled with a separate heli tail gyro.

I wanted to see if I could do it with  the APM. I initially failed because I had some settings wrong, then moved to an airplane stabilizer, then a beastx flybarless system, then back to APM traditional heli. all "worked" but the APM was the best option and allowed much greater control over servo travel and p gain

The thing is from my experimentation - it is almost there. The geometry similarity with traditional heli swash suggests that modifying the firmware for the traditional heli may be the starting point to getting this more stable. the variable pitch responds instantly so gains and servo travel need to be much lower than I anticipated

I am hoping you guys may take an interest in this (time permitting of course) and see if mods to the firmware could be made. Also a question - with the current firmware is there a bottom to the stabilize P.  I am using very low P's - is there a point were the p is outside the range expected by the stabilization algorithm?

Thanks

Al

Moderator Comment by John Church on March 13, 2012 at 10:58pm

Hi Al,

Just a quick thumbs-up for a very cool project! Next rev. single motor belt-drive? ;)

Developer Comment by Randy on March 14, 2012 at 4:35am

@Al,

     Re making very small P values - it gets difficult to set them through the mission planner if they're less than 0.001 (it only displays 3 decimal places) but internally there's no particular limit as they're all stored as floats.

Comment by Ellison Chan on March 14, 2012 at 7:35am

Very nice, we should write a special motors code for Al.  Basically, I see that instead of setting the motor speeds based on yaw/pitch/roll, we just set the throttle, and control the servos.  One channel for throttle, and 3 channels for servos.  A variant on Y3 config.

I'll take a stab at it, if you want to alpha test, Al.

Comment by Wessie on March 14, 2012 at 10:21am

Great Project Al, I have been thinking about this for some time for a quad, especially if one makes a really big one, capable of lifting 5-10kg. was thinking about using 450 heli heads with a locked swash for pitch on the blades, because larger props have more inertia, and therefore more difficult to respond quickly enough for crisp stabilisation.

Keep at it, were following you with great interest...

Comment by Al Ros on March 14, 2012 at 9:33pm

Thanks Guys for your support !!

I'll keep plugging away but certainly any help on the firmware side would be great.

Yes the single motor with belt driven rotors would be a step up for sure. I am looking at using 450 size tail rotors. Will keep you posted

Al

Comment by Jeff Zika on April 4, 2012 at 9:23am

Good job so far. I haven't used APM for a tri but have used 4 gyros several times with good success. Basically, you need a gyro on each swash channel then another for yaw control. The gyros are in-line between the receiver and speed controllers. With a LOT of trial and error tuning it can be done. There are some great tutorials out there on how to do it this way. 

FYI... rig a tripod base  to attach the tri to while working out the gyro geometry and use much smaller props than normal. Been there done that and have the scars to prove it. 

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