TREX250 Tail analysis, spacer upgrade and Chinese weights

[hotdogbun]

Looking for Heim Joint. I sent you a PM with the quantity and type of some of the chinese nuts I need. I'm from Singapore. Pls let me know if you are able to deliever over here. I have given you my email for contact purposes and also my paypal email. Pls let me know. Thanks.

[aussiemick]

I got mine the other day and have them fitted onto all of my helis.
The only thing I am going to change is I will be drilling the thread out of the back side of the tail grip next time I have to remove teh blades. I found it a PITA getting the tail blade tension just how I wanted it and keep it there during the tightening maneuver. I reckon the "chinese nut" will hold the right tension on the blade all by itself, and simplify blade changes.

All very nice work, thank you HJ for a top product.

Mick

[OICU812]

Here is my set fitted on the 250, also got and installed the preload spacer set, thanks HJ!!

[De GooF]

Today i was trying to fit the pre-load bearing but i can't fully seat them in the grips. Tryed the original way with 1 bearing per side without pre load bearing it fits,but still have side play. Wich part number do i need to get so that i can fit 2 bearings per side ?



Jan-Willem

[HEIM JOINT]

Originally Posted by De GooF

Today i was trying to fit the pre-load bearing but i can't fully seat them in the grips. Tryed the original way with 1 bearing per side without pre load bearing it fits,but still have side play. Wich part number do i need to get so that i can fit 2 bearings per side ?



Jan-Willem

Watch the instruction video

T250 Preload spacer assembly (10 min 0 sec)

If you have single bearings in your tail you have to buy (4) 1.5 X 4 X 1.2 bearings anyway to use the spacer set. The Gaui bearings seem to be better quality and are what help cure the problem in the video. They also cost twice as much as the Align 681X bearings. Buy (2 packs) of Gaui # 203250 from your favorite hobby shop to go with the spacer set. Don’t worry that the Gaui bearings are called 1.4 x 4 x 1.2 they actually are 1.5 x 4 x 1.2. You may also have to trim a little off the blade where it might touch the new longer screw that goes thru the bearings.

[De GooF]

I have watched the video,but thanks for clearing it up.
Cant wait to install it

[Thrashaero]

While this may not be nearly as bad on main rotor (RPM I suppose), wouldn't it help to have weights there or is it really negligible?

If we can zero the force required for the tail, how do we zero the force required for the main rotor?
High torque servos for cyclic wouldn't be necessary would it if possible? Does the flybar complicate matters?

[helidude3]

hmm, a flybarless head w/ chinease weights. Sure is an interesting idea.

[HEIM JOINT]

Originally Posted by Thrashaero

While this may not be nearly as bad on main rotor (RPM I suppose), wouldn't it help to have weights there or is it really negligible?

If we can zero the force required for the tail, how do we zero the force required for the main rotor?
High torque servos for cyclic wouldn't be necessary would it if possible? Does the flybar complicate matters?

Yes the tennis racquet effect is there on the main rotor. And yes it is much less because the rpms are much lower. and weights can be made for the main rotor.

If you only used collective on the main rotor then it would behave the same as the tail rotor. Chinese weights would reduce the force required to go to full pitch either direction and the collective pitch setting would stay where you put it.
But as soon as you apply any cyclic there are inertial forces in the main rotor because you are constantly changing the pitch of the blades each revolution. It takes force to make the blade pitch accelrate and decelerate thru whatever range of pitch the swashplate angle is forcing the blades to follow. Chinese weights would not change these forces.

I do intend to test Chinese weights on the main rotor of the T250. I will post a video when I get to it.

HJ

[helidude3]

even though theoretically it might not work, it still could in real life.

[toyturbo]

Originally Posted by raginredneck93

The only way it'll work better is if the metal tail control arm eliminates the slop between it and the plastic ball on the pitch slider. That's the only place that there's any slop left in mine. If it doesn't eliminate the slop, then it's nothing more than bling as I'm sure the plastic one is quite strong enough. I'm considering attempting to fill the hole in my plastic arm with epoxy, and then redrill it smaller until the pitch slider ball JUST fits. Might just be the ticket.

I gotta ask, will the entire tail assembly from a Gaui 200 fit? How about just the rotor itself and the slider?

Actually the new metal pitch slider has a longer pivot point compared to the stock plastic one. The ball is positioned further from the attachment point (4-5mm) which creates better mechanical leverage thus increasing tail control/authority. The tail servo doesn't have to move as much to get the same pitch deflection, easing the load on the servo. I would recommend getting one if I were you!

[Vinger]

Originally Posted by toyturbo

Actually the new metal pitch slider has a longer pivot point compared to the stock plastic one. The ball is positioned further from the attachment point (4-5mm) which creates better mechanical leverage thus increasing tail control/authority. The tail servo doesn't have to move as much to get the same pitch deflection, easing the load on the servo. I would recommend getting one if I were you!

If the ball is further out, YES on the mechanical advantage but a definite NO on less servo movement ACTUALLY more servo movement for the same effect at the tail.

LONGER ARMS = LESS throw

[harryboe]

Originally Posted by Vinger

If the ball is further out, YES on the mechanical advantage but a definite NO on less servo movement ACTUALLY more servo movement for the same effect at the tail.

LONGER ARMS = LESS throw

I don't agree! It's more like using the full servo travel.

SAME ARMS = MORE throw / MORE resolution / LESS speed

.. and speed was not the issue so far.

[Thrashaero]

i have the longer arm metal bellcrank...and it has significantly reduced my overall throw.

i'm also not particularly impressed with how there's slop with it vs. the bushing it comes with.

[Vinger]

Originally Posted by harryboe

I don't agree! It's more like using the full servo travel.

SAME ARMS = MORE throw / MORE resolution / LESS speed

.. and speed was not the issue so far.

Maybe I was not very clear in my explanation, but let us try again.

If the belcrank has a longer arm (where the pushrod attaches), then with the same arm lenght on the servo side, one would get LESS pitch change (throw) than before. The torque required from the servo would be reduced as you now have mechanical advantage from driving a longer arm from a shorter servo arm, comparitively speaking, BUT definately reduced pitch change range.

If you still can't understand it, picture a small pinion driving a large gear - large gear moves slower, but has more torque. The reverse of a larger pinion will drive the gear faster is also true, but with less torque than before. Hope it is clear as mud now.........

[helidude3]

guys, what ever, there has been evidence that there is less servo travel so you must be right. Anyway, Can't you just use a longer arm. Instead of putting the ball at 5mm, you put it at 7 or even a little more to get max travel?

[Mikej]

Having a longer arm on the bellcrank means that you will need less power, but more movement to create the same amount of movement at the tail slider. This means that you can use a less powerfull (less torque) servo and that you will have greater resolution (accuracy) as the servo will have to move more - all sounds good to me

Mike.

[rotary65]

Hey guys, the Trex 250 I just got from Flying Hobby has tail grips with built-in weights. Are these as effective or not? Should I still install Heim Joint's weights or will it be too much?

[HEIM JOINT]

Check out the test of them https://www.helifreak.com/showthread...=130227&page=3 post #1

HEIM JOINT

[rotary65]

Thank-you very much much for the link. From the video, the Align weighted grips reduce the force to 5 oz at 20 degrees pitch. Since your weights on the stock grips reduce the force required from 6 oz to 1.5 oz, is it reasonable to assume that adding them to the weighted grips will result in a further 1 oz reduction ( to .5 oz)? If so, that will reduce the loading beyond the ideal point of 1.5 oz. Perhaps it will not be that dramatic a reduction.

Should I modify your weights (once I receive them) to reduce their weight to compensate or just install them as-is?