RC Helicopter: T-Rex 250 gyro ground test Align GP750 & DS420

Click 'more' to read all the technical details...
Ground-testing a Align T-Rex 250 helicopter. The machine is mounted on a strong rotatable platform made from Lego to test the gyro/rudder. Any increased load from RPM or pitch will produce torque variations, the gyro detects uncontrolled movement and will send corrections to the tail servo to keep the tail in the same position. A wrong setup may cause drifting (uncontrolled rudder) or tail wag (over-correcting, the tail keeps shaking left and right)

Setup:
- Gyro Align GP750
- Tail servo Align DS420 (digital)

Gyro setup:
- Frequency 1520 (red)
- Digital (green)
- Reverse on (red)
- Both limits set
- Delay: large heli (red) to allow more gain

Transmitter Graupner MX-12 (JR 6102)
- Gain heading hold mode: 42%. Less will cause drift, more will cause tail wag.

Mechanical setup:
- Most important: The gyro is hold in place only by the double sided foam. Any attempt to tighten it with tie-wraps will make it more sensitive to vibrations, causing HEAVY tail wag! The gyro is located on the recommended position, on the gyro tray on the back.
- Weights (bolts) on tail blade screws on the outside. During rotation less force is needed to change pitch, so the servo needs to apply less force too. I also tested without weights, the servo handles that fine too.
- Lubricated tail belt to improve overal performance
- Round servo arm because that's the strongest one. Altough tests with other servo arms performed the same.
- Short ball link, because the long ball link moves a bit under load. Tests with the large ball link didn't show any increased tail wag though.
- Ball link in the hole closest to the servo center (5 mm). I used glue to tighten the ball link in position. Tests with the ball link on the outside caused heavy tail wag.
- Tail blades and rotor blades: stock/default, but custom airbrushed yellow/blue for visibility
- Central tail rod holder glued to tail boom, so the tail rod can't flex. A flexing tail rod may produce tail wag.
- Moving the tail rod by hand at full throttle feels smooth, so the rod won't flex/cause wag.
- Check the tail blades and rotor blades for balance, unbalanced blades cause vibration which might disturbe the gyro.

Category:

Science & Technology

Tags:

• align
• trex
• 250
• t-rex
• gyro
• gp750
• ds420
• test
• ground
• tail
• wag
• heading
• hold
• drift

[jasmine2501]

Groovy blades dude! Definitely would help with visibility. Great idea!

[MiniaviationDotCom]

Thanks dudette! It's nice to read a comment here from the T-rex 250 guru herself.

The bottom side of the blades have been painted the opposite way, it's gives a nice visual effect during transitions from top/bottom view. Revell paint colors 12 (gloss yellow) & 51 (gloss blue)

[jasmine2501]

Cool... I have some of that :)

It didn't throw them off balance or anything?

[MiniaviationDotCom]

The center of gravity is good, the balance is off by only 2 degrees, so it seems okay.

The paint layer is very thin because it's airbrushed.

[MiniaviationDotCom]

The helicopter is mounted on a rotatable platform made from Lego.

Testing the gyro and tail servo under load, variating pitch and motor RPM.

Click on the video's "more info" link to read all the technical stuff.

[lockpicker2k]

@Driftking3268

A delicious Greek sandwich!

[mrrjcook]

is the red thing a speed up

[SamuelChung94]

hey i have a question, is the the tail belt driven? or does it have a motor there like many indoor helis

[ecoovert]

I am new to helicopters and am having trouble with my rudder being way to sensitive. When I try to hover my copter spins in one direction so I move the trim one click in the opposite direction which causes the copter to spin in the opposite direction. Is this a sub trim issue in the radio settings or is it a physical issue like moving the rudder control rod one hole closer to the center of the servo horn on the rudder servo? If a radio issue how do I reduce the rudder sensitivity?

[MrBinkynator]

Science. Gotta love it. :)

[7249xxl]

you know if did the same onley from lego and it works and flies but not far 20 meters and than the rotor blades explode but i made them from paper but im gluing them now and it worsks good

[hoffbran]

flip idle up switch on basically puts your head speed at a constant, then wen u go upside down bring the throttle stick all the way down like badbram said and you will stay in the air

[p4n0sgr]

haha right :)

[pynqlydz]

hey can i use my walkera transmitter 8ch for trex 250

[Driftking3268]

I know this is a stupid question but what is a gyro?