Originally Posted by ghoffman

The MKS carbon fiber arms and hubs have an odd number of splines on the hub (25T) and an even number of screws for the CF arm. This works like a Vernier so one can get it really close.

+1

Used them recently to set up my EX Flight 125" extra on Hitec D951 servos resulting in Zero sub-trim on any flight surface servo!

Get the 6MM hubs for the arms and they will go on any Futaba spline servo.

Thanks for all the responses guys. I've moved the servo arms forward to eliminate the differential. Should have thought of that myself. Anyway it worked great and now I've got exactly the throws I want.

I'm completely sold on the MKS hubs and already had one on this airplane. On the few airplanes I've worked with, because of the odd number of teeth, I've found one aileron servo arm has typically lined up perfectly and the other is off by 1/2 tooth which means lots of subtrim (25 on my DX9). With an MKS hub on that side, subtrim drops to zero. The improvement in geometry can't be overstated. With today's geometry change, I do need to use some subtrim on the other side so I'll be picking up another MKS hub.

The 9177 servos came used with the plane and showed signs of gear wear so I replaced those while the arms were off. Also added weight to correct a slightly heavy wingtip, and downthrust to correct a pull to the canopy on uplines and full-throttle straight & level flight. Fingers crossed that this already wonderful little airplane will fly even better.

Though the little 73" is kind of out of scope to this thread, I do have a 105 on order. Actually it'll be the 3rd one shipped to me. Despite AJ's terrific crating, the shipping company managed to mangle the first two. Sigh. I'm enjoying the 73 but can't wait to get the 105.

Originally Posted by randomguy

I bought a previously owned AJ 73" Laser - fantastic airplane - and am converting the setup from 3D-capable to a strictly precision IMAC practice plane. Among other things, I'm installing shorter servo arms.

With the original 1.25" arms, I had exactly the same throw both up and down. With my new 0.55" SWB arms, I'm getting 20 degrees up and 25 degrees down. That's a huge unwanted differential. I need to get back to identical throws mechanically, without programming.

The radio setup doesn't seem to be a problem: servo travel, endpoints and rates are identical in both directions (maxed out), subtrim is zeroed, and servo arms are as close to perfectly parallel to the hinge line as I can measure. Transmitter confirms the servo travel is 0 at center and identical in both directions.

What’s changed is the pushrod angle, since the servo end of the pushrod is now 0.7" further inboard than it was before. So I ran a bench test, moving the aileron end inboard by about the same amount, so it’s no longer wedged between the two control horns but instead sits inboard of them on a longer screw (see photos). That gets me back to identical throws up & down. Nice!

But this setup would place a torque on the double control horns that they’re not designed to take. It seems destined for premature failure.

Is there a different way to achieve equal up and down throws mechanically with these shorter servo arms that won't add additional strain on the airframe? I suppose I could add another control horn in the new inboard location but that would require cutting the aileron covering to add a mounting block - and it would look strange (I’d leave the originals in place to have the option of going back). It seems like heresy on such a beautifully built airplane. Obviously I'd prefer something less invasive.

Has anyone else done this?

Just looking at the linkage, the ball link should be captured on both sides of the control link. Not sure what’s going on there. Usually my servo arm is angled to give me the best up and down throw with the atvs maxed out as far as they can go before any binding occurs. It’s not uncommon to see the numbers be off up from down. Usually futaba will be in the 120- 140 range, I believe JR and Spektrum are in the 130-150 range with the maximum amount of throw you want.

So I understand what you are trying to achieve in the picture, and with my limited knowledge of setting up planes for precision flying I'd have to ask if the benefits of the extra resolution from a .55" arm out weigh the advantages of having to potentially modify the plane so that is can be setup mechanically perfect?

Originally Posted by Surfer Dude

Just looking at the linkage, the ball link should be captured on both sides of the control link. Not sure what’s going on there. Usually my servo arm is angled to give me the best up and down throw with the atvs maxed out as far as they can go before any binding occurs. It’s not uncommon to see the numbers be off up from down. Usually futaba will be in the 120- 140 range, I believe JR and Spektrum are in the 130-150 range with the maximum amount of throw you want.

From my original post:

Originally Posted by randomguy

So I ran a bench test, moving the aileron end inboard by about the same amount, so it’s no longer wedged between the two control horns but instead sits inboard of them on a longer screw (see photos).

[...]

But this setup would place a torque on the double control horns that they’re not designed to take. It seems destined for premature failure.

[...]

Is there a different way to achieve equal up and down throws mechanically

I included the photo as an illustration of a geometry that solved the problem on my workbench. No intention to fly it that way.

Originally Posted by MikeDobies

So I understand what you are trying to achieve in the picture, and with my limited knowledge of setting up planes for precision flying I'd have to ask if the benefits of the extra resolution from a .55" arm out weigh the advantages of having to potentially modify the plane so that is can be setup mechanically perfect?

@MikeDobies - I agree which is why I posed the question here to benefit from peoples' collective wisdom. Had the answer by the next morning. Just needed to rotate the servo arms. Couldn't be easier, and I learned something useful for future setups.

The forums can have massive amounts of clutter and junk but they can also be pretty valuable. Thank you again to everyone who replied.

Took advantage of the spring weather this weekend to turn out some flights on the Laser. Unfortunately all of this spring weather also means my allergies are a wreck! But still got a gratuity of stick time in

Originally Posted by randomguy

@MikeDobies - I agree which is why I posed the question here to benefit from peoples' collective wisdom. Had the answer by the next morning. Just needed to rotate the servo arms. Couldn't be easier, and I learned something useful for future setups.

The forums can have massive amounts of clutter and junk but they can also be pretty valuable. Thank you again to everyone who replied.

hello ..
i have a 105" laser, and i am going for imac. i had 1.75" servo arms in my elevators setup, and in imac f-mode it worked at 18% of max travel to fit my need for precise flight.
now i have shortened servo arms to 1.25" .
the angular travel is the same, but now it works at 32% of max travel.
strange enough, i do not feel a great difference between the first setup and the current one.
i told to myself the answer is in great resolution our radio and servos have nowadays.
probably a better pilot than me would " feel the difference"..

Upgraded the motor on the electric 105" and now ready for Nall.
Power is right up there with 120cc gas although the flight times...not so much. But I'm still able to manage 6 minutes so I can live with it. Might make the jump up to 10,000mah packs from the current 8,000mah for an extra minute of flight time.

Electric 105 AJ Laser (6 min 26 sec)

Can't remember is this the same plane with the gear reduction?

Originally Posted by Flybye Steve

Can't remember is this the same plane with the gear reduction?

Yes this is the same plane. I've upgraded the motor wind (hotter) in this latest edition and now I'm satisfied with the final result.

We had some great weather in Arizona this past weekend, I couldn't help but go fly:

AJ Aircraft Laser 230Z 105" Freestyle (8 min 21 sec)

I upgraded the servos as well, changed from HSB-9380TH to HSB-9381TH full aluminum case servos. The airplane feels more crisp and obviously flies incredible

Here are some pictures from Saturday that Chris from www.thercgeek.com was able to capture for me.


I got one 10min flight in, and then the rain came pouring in and I had to pack up. Still always a blast on this plane!

What club is that?

Nice