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Old Sep 15, 2010, 03:14 PM
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Ilford,Essex, UK
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Quote:
Originally Posted by SkyEyes View Post
Eeek - My passing question on where the CofG would be (or how to calculate it) on a " T " shaped Tricopter has really created a storm.
I apologise guys! Perhaps I will go back to my wife (who teaches Sciences/Mathematics) and ask her, from a Trigonometry standpoint. lol

I did read in another thread that the COG is not the same with a T copter

Some builds are using a smaller motor on the tail and the COG is close to the the top of the T, there are some real "different" concepts on RCG threads

Regards Jeff
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Old Sep 15, 2010, 03:19 PM
Aerial Images of Texas
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The Texas Gulf Coast where hurricanes come to play
Joined Aug 2003
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Quote:
Originally Posted by signguy View Post
Get out the paper, and a place to draw. Draw your motors spaced the way you like. next draw a standard 120 degree frame to connect the motors. Then, draw a T to connect the motors, or any style frame, swept, less than 120 degree......

The CG falls at the intersection of the 120 degree arms. Thats it, no trig needed...

BobD
That's only if the rear arm is as long as the arm that connects the front motors. So, is that the proper configuration for a "T" Tri? Front arm and rear arm the same length? Orrrrrrrr, should it be the same as your Tri design we have all built... each arm equal length.
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Old Sep 15, 2010, 03:20 PM
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Originally Posted by tashley View Post
If you use that formula for locating the cg the machine will be way nose heavy. On a fixed wing aircraft the cg is about 30% of the mean cord from the leading edge but on a tri motored craft all three arms should be equally balanced just as a heli should balance directly on the main shaft. As an experiment cut two sticks one half as long as the other. Now glue the short stick to the center of the long stick and placing your finger tip on the bottom side of the short stick move it fore and aft till you get balance. Now see where your fingertip ends up. When your finger is placed so that the sticks balance fore and aft, you have found your proper cg, static model or flying model, it dosen't matter.
I don't have experience in building and flying a "Tee" Tri but I do know a thing or three about balancing aircraft.
I agree just a healthy debate as long as I am right

Hi Tashley I presume you meant mine would be tail heavy as it is behind your point. I still think you got it wrong I wasnt talking about balancing a plane but where to get the CG so that all 3 motors carry the same load. Lets rather put it like this. Forget the Left and Right as we know they are symmetrical and therefore the CG will be in the center. Lets focus on looking just front to back. 2 motors up front and one at the back. Twice the lifting power at the front than the back. Therefore you should have half the length from the CG forward to what you have to the back.

I'm guessing that you saying if you widen the 2 front motors on a tricopter (which is the same as making the tail shorter in relation to 2 front motors) then your CG should start shifting forward to keep the weight equal on the motors yet no weight has changed forward or backwards in this example
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Old Sep 15, 2010, 03:31 PM
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Ilford,Essex, UK
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COG on a T

Have a look at some of skycam4's work

Or who needs a tail anyway

http://www.youtube.com/user/KapteinK.../3/bRdACGb1wBQ
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Old Sep 15, 2010, 03:32 PM
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Quote:
Originally Posted by tashley View Post
As an experiment cut two sticks one half as long as the other. Now glue the short stick to the center of the long stick and placing your finger tip on the bottom side of the short stick move it fore and aft till you get balance. Now see where your fingertip ends up. When your finger is placed so that the sticks balance fore and aft, you have found your proper cg, static model or flying model, it dosen't matter.
Hey Tashley, I think this is where you went wrong. This shows you where an object does balance and not where it should balance for aerodynamic reasons. If you made a stick aeroplane without any engine it would balance half way down the fuze... Please dont fly it at that CG

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Old Sep 15, 2010, 03:35 PM
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Originally Posted by Upup View Post
COG on a T

Have a look at some of skycam4's work

Or who needs a tail anyway

http://www.youtube.com/user/KapteinK.../3/bRdACGb1wBQ
Haha... Thats awesome
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Old Sep 15, 2010, 04:02 PM
Aerial Images of Texas
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The Texas Gulf Coast where hurricanes come to play
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Entertaining but it has nothing to do with the discussion we're having. Ok, so you don't get my experiment with the sticks, try this. Take out the outer bolts from each front arm and fold them back so they're in line. Now check the balance point with that configuration. Hint, it will not be thirty percent back from the front arms. Then adjust your equipment so the cg falls at your thirty percent and fly it that way. Let us know how it goes. Besides, aerodynamics are not really in play here. All we want cg wise is to have each motor with an equal balance relative to the other two.
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Old Sep 15, 2010, 04:22 PM
X-Ikarus
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United Kingdom, North York
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OK. I will post as much info as I can

I'll split this into the basic steps of each stage
in the order I recommend, a sort of mini tutorial

Questions are welcome to complete each stage
but please no discussions on theory or method
you can discuss later, if you have any better methods to try.

Hopefully this will get more Tri's in HH

Paul
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Old Sep 15, 2010, 04:37 PM
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Originally Posted by Reflex1 View Post
You still doubt ............. ?

Statement. My Tri is in HH on ALL FOUR Gyros
The last video link I posted shows this

I disagree with you totally on Vibration it IS the Root cause of problems on HH

Reread this post so I don't have to repeat myself
http://www.rcgroups.com/forums/showp...postcount=9213

I have No special mixes,No Tricks and its not Magic
I also resent your posts implying I don't know what I'm talking about.

The people that know me, know better
I have No need to prove anything to anyone

Paul
I have just put my Tri on the ground with a spare separate HK401 connected to it. Attached with extension leads and fixed to the carpet so that it is completely isolated from the Tri. Meaning... absolutely no vibration. I have set up 2 channels on my receiver so I can try different gains had signal settings. I tried analogue, digital as well as limits and delays. Considering the focus should be vibration isolation the rest was just done for in case. It does exactly as I expected. The throttle runs away to either full or no power

Please guys be very aware when working in HH mode. If you not clued up with how a HH gyro works it can jump up and bite you... literally. For a HH gyro to sense an error and try correct for it by taking the motor to full power is very common. While testing different things be very aware and preferable tie your tri down.

Reflex I would test that your gyros are in HH and not just by checking the lights. Maybe you have a bad batch where the LED's do what they supposed to but the gyros are still staying in rates mode. Looking at your video it still looks like in rate mode or you have narrowed the correction field so much it acts like in rates mode. On the few occasions where you did a long slow downward push the motor seem to react to the initial rotational acceleration and then remains the same where as in HH the motor should react more and more as it goes down. As far as some doubting, I think we all entitled to doubt as there are plenty of guys on forums who love the power of sending others on a wild goose chase. It happens very often!

For now I'm happy to just say it doesnt work
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Old Sep 15, 2010, 04:49 PM
X-Ikarus
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United Kingdom, North York
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If the Gyro is not on the Tri HH will do that
The Gyro will keep sending corrections until its at the position demanded.
Since it can't Move the Tri. it will end up at its stops.

This will not happen in flight
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Old Sep 15, 2010, 05:02 PM
X-Ikarus
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United Kingdom, North York
Joined Feb 2003
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HH Tutorial. Stage 1

Heading Hold Tutorial. Stage 1

Step one

1. Remove Props and Adaptors From All Motors
2. Remove esc plugs from Gyroís
3. Refit One esc plug to itís Gyro (this will be the motor your working on)
4. Power up the Tri as normal, note. Only one motor will run
5. Balance Motor as explained at http://www.rcgroups.com/forums/showp...postcount=8839
6. You have to be Super Critical, you MUST reduce vibrations to an absolute minimum. Lightly touch the boom near the motor to feel vibes.
7. If you can feel any vibes on the Gyro cases You Will Have Problems Later
8. remove the esc plug from the Gyro

Step two
Repeat the above for the other motors
Only run One Motor at a time

----------------------------------------------------------------------------------------

Troubleshooting

If you can't achieve a vibe free motor
1. Check motor bearings are smooth and free running
2. the motor shaft may be bent
3. any magnets loose ?

either repair or replace the motor

----------------------------------------------------------------------------------------------

Tip. If you donít have any Thick CA (as me)

Buy some Bicarbonate of Soda (Baking Soda)
Put a mound were you want to add weight and drip Thin CA on it
It dries Very quickly and sets like concrete
Over weight it and sand to fine adjust balance


Paul

Motor Picture, left to right
BiCarb and CA ,Tie wrap and original motor
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Last edited by Reflex1; Sep 16, 2010 at 07:24 AM. Reason: Troubleshooting added
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Old Sep 15, 2010, 05:16 PM
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Quote:
Originally Posted by tashley View Post
Entertaining but it has nothing to do with the discussion we're having. Ok, so you don't get my experiment with the sticks, try this. Take out the outer bolts from each front arm and fold them back so they're in line. Now check the balance point with that configuration. Hint, it will not be thirty percent back from the front arms. Then adjust your equipment so the cg falls at your thirty percent and fly it that way. Let us know how it goes. Besides, aerodynamics are not really in play here. All we want cg wise is to have each motor with an equal balance relative to the other two.
You know what you doing?? You creating rivalry Ok so I did what you said. I straightened the front arms so its like a T-shape tri. From the T intersection to the rear motor is 534mm. 33% of that is 178mm. I used my Lipo with elastic and moved it around the back boom until it balanced at 33%. I then got my digital scale and some equal height packing. I measured the weight of each motor under the center of the motor and got the following readings

Left front 356g
Right front 359g
Back 348g

I think that is close enough but if anything it needs to come back a tiny bit more. Thats probably because its supposed to be 33.333333%

Are you happy now
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Old Sep 15, 2010, 05:34 PM
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UK, Redcar and Cleveland, Redcar
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Thanks Paul I'll be starting mine as soon as the new shop is done as its full 16 hour days at the moment what with work and new home.

Looking forward to seeing the HH tri, give me a ring next time your off to the field on a weekend and I'll call down as I'm only 2 minutes from there.

Keith
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Old Sep 15, 2010, 05:48 PM
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Quote:
Originally Posted by SkyEyes View Post
Eeek - My passing question on where the CofG would be (or how to calculate it) on a " T " shaped Tricopter has really created a storm.
I apologise guys! Perhaps I will go back to my wife (who teaches Sciences/Mathematics) and ask her, from a Trigonometry standpoint. lol

Check this thread out. About 1/4 of the way down the page

http://www.rcgroups.com/forums/showt...6#post15979688
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Old Sep 15, 2010, 07:27 PM
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Belgrade, Serbia
Joined May 2010
461 Posts
SloMo in forest

sumaslow (1 min 8 sec)


and one more with girls playing football

fucasuma (2 min 4 sec)
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Last edited by dragant; Sep 15, 2010 at 09:03 PM.
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