SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Apr 10, 2011, 12:51 PM
Registered User
Joined Oct 2004
2,810 Posts
Tom, it does not work like that, because there's nothing to hang from. The thrust vector tilts with the plane, there's no net rightening moment
Brandano is online now Find More Posts by Brandano
Reply With Quote
Sign up now
to remove ads between posts
Old Apr 10, 2011, 04:49 PM
Registered User
RCvertt's Avatar
Joined Aug 2007
4,149 Posts
Quote:
Originally Posted by Brandano View Post
Careful there. the fact that the props are forward or back of the CG does not have an effect if the tilting point is through the thrust axis...
Got it, thanks.

Quote:
Originally Posted by Tifani View Post
I'm in progres of making "Panther UAV" ...
You wrote than Your Tri is not very stable - I will try to mak it solid hover first...
Good to see you building one also.

Same here on the hover. I'll build a tri with no fuselage first, then move the cg back to match the airplane build and see how the tri reacts, then go piece by piece from there. Too many variables currently going on.
RCvertt is offline Find More Posts by RCvertt
RCG Plus Member
Last edited by RCvertt; Apr 10, 2011 at 04:56 PM.
Reply With Quote
Old Apr 10, 2011, 05:55 PM
Registered User
United States, IL, Park Ridge
Joined Apr 2010
211 Posts
Hi !
I think to match CG of Tri with CG of wing assuming CG of wing @ 25-30% of the chord. Probably best to test CG of wing before attaching Tri.
Drawing is for constant chord wing but will work with any shape of wing as long both - CG of Tri and CG of wing are the same.
\My first gyro only Tri was 100% stable (even I can fly it) because was very well balanced.
Tom
Tifani is offline Find More Posts by Tifani
Reply With Quote
Old Apr 10, 2011, 06:01 PM
Registered User
rimshotcopter's Avatar
United States, CA, Los Angeles
Joined Aug 2009
11,700 Posts
Tifani, IMO, I believe it would be better to focus on the Center of Thrust. With a Tricopter, it just so happens that when all three motors and props are the same, the CG and CT match but this is not always true.
rimshotcopter is online now Find More Posts by rimshotcopter
Reply With Quote
Old Apr 10, 2011, 06:09 PM
Registered User
United States, IL, Park Ridge
Joined Apr 2010
211 Posts
Hi Rev !
100 % right - but easiest way to start is :"when all three motors and props are the same"
Tom
By the way - do You have any formula to calculate CG for diferent size of rear motor/prop. or size of motor/prop. foc particular CG ? - loks I will need it for my Bi.
Thanks
Tifani is offline Find More Posts by Tifani
Last edited by Tifani; Apr 10, 2011 at 06:16 PM. Reason: forget to ask
Reply With Quote
Old Apr 10, 2011, 06:11 PM
Registered User
rimshotcopter's Avatar
United States, CA, Los Angeles
Joined Aug 2009
11,700 Posts
I agree.
rimshotcopter is online now Find More Posts by rimshotcopter
Reply With Quote
Old Apr 10, 2011, 06:16 PM
Registered User
rimshotcopter's Avatar
United States, CA, Los Angeles
Joined Aug 2009
11,700 Posts
I don't know if you guys have seen this video but it may not harm to review it.

Vtol Verti4 crespiere 2008 (3 min 1 sec)
rimshotcopter is online now Find More Posts by rimshotcopter
Reply With Quote
Old Apr 10, 2011, 10:10 PM
Registered User
RCvertt's Avatar
Joined Aug 2007
4,149 Posts
Quote:
Originally Posted by Tifani View Post
...Probably best to test CG of wing before attaching Tri...
This is where the airframe puts the CG on my tri currently.

Quote:
Originally Posted by reverendrichie View Post
I don't know if you guys have seen this...
Good to see that again. Looks like his pitches up also when he goes from ForwardFlight to HoverFlight modes. Looks like he also gives some down elevator control from HF to FF to prevent the nose from pitching up.

So basically I think I'm having the same issue except I have less forward pitch power since I only have one motor in the back, the rear motor is closer to the cg so it has less leverage and there is a bunch of wing area in the back making the rear motor even less effective.
RCvertt is offline Find More Posts by RCvertt
RCG Plus Member
Last edited by RCvertt; Apr 10, 2011 at 11:10 PM.
Reply With Quote
Old Apr 11, 2011, 03:43 PM
Registered User
Joined Oct 2004
2,810 Posts
You also have a lot of "spare thrust" from the front motors, seeing how far forward of the CG they are. Have you tried to throttle back the front motors through conversion while keeping the rear one near max?
[edit] or you could add a canard and shift the CG forward
Brandano is online now Find More Posts by Brandano
Reply With Quote
Old Apr 11, 2011, 07:21 PM
Registered User
RCvertt's Avatar
Joined Aug 2007
4,149 Posts
Quote:
Originally Posted by Brandano View Post
You also have a lot of "spare thrust" from the front motors, seeing how far forward of the CG they are. Have you tried to throttle back the front motors through conversion while keeping the rear one near max?
[edit] or you could add a canard and shift the CG forward
Good ideas. I throttled up the rear motor to compensate for the extra thrust of the front props. The rear motor probably hit it's max too soon so it couldn't compensate any more. Reducing the front thust as you suggest is a better idea that I'll try.

I like the canard idea if they go in front of the motors and extend out a little further than the props to help guard against prop strikes. That's almost an entire wing length though but I'll keep it in mind.
RCvertt is offline Find More Posts by RCvertt
RCG Plus Member
Latest blog entry: Chupacabra sighting !!!
Reply With Quote
Old May 15, 2011, 06:56 PM
Registered User
RCvertt's Avatar
Joined Aug 2007
4,149 Posts
@ cass3825- Can you add to the zip file servo control for pins D22, D23, D32, D33, D34 for the mega? Servo slow and stretching on D32 and D33 would be great.
RCvertt is offline Find More Posts by RCvertt
RCG Plus Member
Last edited by RCvertt; May 21, 2011 at 03:23 PM.
Reply With Quote
Old May 21, 2011, 03:15 PM
Registered User
RCvertt's Avatar
Joined Aug 2007
4,149 Posts
Almost got the servo movement set up perfectly.

The only thing is that the front right servo doesn't travel far enough. When the servo is pointed up or forward it stops moving even though there is still a little stick movement left. It's noticeable the most when the servo is forward and is commanded down with the pitch stick.

Attached is the code drop I'm using
ServoNotMovingFarEnough (0 min 47 sec)
RCvertt is offline Find More Posts by RCvertt
RCG Plus Member
Last edited by RCvertt; Oct 29, 2011 at 08:39 AM.
Reply With Quote
Old May 21, 2011, 03:37 PM
Registered User
rimshotcopter's Avatar
United States, CA, Los Angeles
Joined Aug 2009
11,700 Posts
Nice, in fact VERY Super Nice.
rimshotcopter is online now Find More Posts by rimshotcopter
Reply With Quote
Old May 21, 2011, 04:12 PM
Registered User
RCvertt's Avatar
Joined Aug 2007
4,149 Posts
Quote:
Originally Posted by reverendrichie View Post
Nice, in fact VERY Super Nice.
Thanks. The work we are all doing is really opening the door to some cool possibilities for us all

If anyone is interested, I've tried to make the ISR portion of the servo code a little easier to use by separating it into separate code chunks that we can copy and paste with minimal changes if we want to add more servos. The current method is a little tangles up for this newb to read.

This currently isn't working good though. The (DIGITAL_MOTOR_TILT) section works fine. It's stretched and centered good but the (DIGITAL_TILT_PITCH) section results in a servo that is pointing forward instead of at the desired 45 degree default position and doesn't seam to be stretched

Code:
static uint8_t carry;


ISR(TIMER0_COMPA_vect) 
{
  static uint8_t state = 0;
  static uint8_t count;
  if (state == 0)                  ////////////////////////////// Start servo[5] DIGITAL_MOTOR_TILT stretching code block///////////////////////////////////////// 
     {
      #if defined(VTOL)
      DIGITAL_MOTOR_TILT_HIGH
      #endif
      OCR0A+= 150; // 500 us
      state++;
     } 
     else if (state == 1)
             {
              if (carry & (1<<5)) OCR0A+= 250; // another 1000 us
              else OCR0A+= atomicServo[5]; // [0-1020] us
              state++;
             } 
     else if (state == 2)
             {
              if (carry & (1<<5)) OCR0A+= atomicServo[5]; // [0-1020] us   // If servo rolls over, reset it and keep moving. Assign DIGITAL_MOTOR_TILT as servo 5.
              else                                                         // Or move normally.
                 {
                  #if defined (VTOL)
                  DIGITAL_MOTOR_TILT_LOW
                  #endif
                  OCR0A+= 150;// 1000 us
                 }
              state++;
             } 
     else if (state == 3) 
             {
              #if defined (VTOL)
              DIGITAL_MOTOR_TILT_LOW
              #endif
              state++;
             }                ////////////////////////////// End servo[5] DIGITAL_MOTOR_TILT stretching code block///////////////////////////////////////// 
  if (state == 4)             ////////////////////////////// Start servo[2] DIGITAL_MOTOR_TILT stretching code block///////////////////////////////////////// 
     {
      #if defined(VTOL)
      DIGITAL_TILT_PITCH_HIGH
      #endif
      OCR0A+= 150; // 500 us
      state++;
     } 
     else if (state == 5)
             {
              if (carry & (1<<2)) OCR0A+= 250; // another 1000 us
              else OCR0A+= atomicServo[2]; // [0-1020] us
              state++;
             } 
     else if (state == 6)
             {
              if (carry & (1<<2)) OCR0A+= atomicServo[2]; // [0-1020] us   
              else                                                         
                 {
                  #if defined (VTOL)
                  DIGITAL_TILT_PITCH_LOW
                  #endif
                  OCR0A+= 150;// 1000 us
                 }
              state++;
             } 
     else if (state == 7) 
             {
              #if defined (VTOL)
              DIGITAL_TILT_PITCH_LOW
              #endif
              state++;
             }                //////////////////////////////End servo[2] DIGITAL_MOTOR_TILT stretching code block///////////////////////////////////////// 
     else if (state == 8)  
             {
              count = 6; // 6 x 1000 us
              OCR0A+= 150; // 1000 us
              state++;
             }
    else if (state == 9)
            {
             if (count > 0) count--;
             else state = 0;
             OCR0A+= 150;
            }
}
#endif




  #if defined(SERVO)
    atomicServo[0] = (servo[0]-1000)/4;
    atomicServo[1] = (servo[1]-1000)/4;
    atomicServo[2] = (servo[2]-1000)/4;
    atomicServo[3] = (servo[3]-1000)/4;
    atomicServo[4] = (servo[4]-1000)/4;
    atomicServo[5] = (servo[5]-1000)/2;
    if (atomicServo[5] > 255) {
      carry |= 1<<5;
      atomicServo[5] -= 250; }
    else carry &= ~(1<<5);
    if (atomicServo[2] > 255) {
      carry |= 1<<2;
      atomicServo[2] -= 250; }
    else carry &= ~(1<<2);
  #endif
RCvertt is offline Find More Posts by RCvertt
RCG Plus Member
Last edited by RCvertt; Oct 29, 2011 at 08:42 AM.
Reply With Quote
Old May 21, 2011, 04:14 PM
Registered User
Joined Feb 2005
473 Posts
Quote:
Originally Posted by reverendrichie View Post
Nice, in fact VERY Super Nice.
No kidding! +1

I'm planning on this same approach with one of leadfeather's F-35 airframes. With pitch and roll handled in this manner, I'm not convinced I even need tailerons. This would definitely save some weight...
cass3825 is offline Find More Posts by cass3825
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion QTD- Quad Tilt Duino (Arduino- Tilt Rotor) RCvertt VTOLs 100 Jun 28, 2012 12:15 AM
Question Tricopter: What rear tilt angle? bb42 Multirotor Talk 3 Oct 15, 2010 09:40 AM
New Product The new Panther tilt rotor UAV from Israel Aerospace Industries Hunter850 Multirotor Talk 2 Oct 06, 2010 08:06 AM
For Sale Rc lander panther complete setup with metal edf/motor/esc/servos/retracts/battery TurboFanElectric Aircraft - Electric - Jets (FS/W) 3 Mar 25, 2010 08:29 AM
Sold RClander Panther 70mm Fan and motor cjdscratch Aircraft - Electric - Power Systems (FS/W) 7 Mar 13, 2010 10:31 PM