Trex 250 geometry

[aralan]

I wasn't able to get a blue LED in cyclic setup on my 250, although I did use the servo horn center to ball distance Walter mentioned. I'm using different servos though, so it's possible that the measurements are slightly different.

Blue is happening out past 7 degrees, the best I'm able to do is red and I'm really stretching it there. I'm a little confused about what to do next.

If I move the ball in on the arm, it will take more servo travel to get the same deflection, which should allow me to get closer to blue at 6 degrees, correct?

*** Corrected, I was thinking about this backwards.

[aralan]

Okay as much as it pains me to take this little thing apart again, I did. I moved the balls in to the inner most hole on the servo horns. Unfortunately there's a little hump on the top of the servos, which causes the ball to bind against the servo case with the ball mounted facing the servo per the Align manual. I reversed the balls to face out instead.

I threw everything back together very quickly, and it looks like I'm getting a blue light close to 6 degrees now. I did a fast and dirty job at it just to see if this improved my situation, before I start epoxying the balls in to the servo horns and all of that. I gave it a quick test flight in my basement and it seems more stable.

I'm waiting for the epoxy to dry now, then I'll remount the servo horns, and run through the setup again more carefully than the temporary re-do I gave it tonight for testing. Then I'll give it another test flight outside tomorrow and see how it goes.

Side note: After doing the 550 I decided that I wanted all of my helicopters to have BeastX. I'm completely sold on it. After doing the 250 I think I've decided that this will be the last thing I mess with smaller than a 550 any time in the near future. Having started off building a 450, and then working on this 250, working on the bigger helicopters is a real pleasure.

[Punkin71]

Remember it is most important to set up for 6 degrees even if you are not quite able to get blue light. I say this because you mention you are able to get blue light at close to 6 degrees

[SidewaysLS4]

Yep, these 250's are kinda tough. I get a red 6* on the border of purple/red, using the 2nd hole in on the DS410 arms with the Align FBL head. I was thinking of moving one more hole in with the ball on the outside of the arm, but the geometry would be bizarre. Anyone see if the servo hump could be dremmeled off for ball clearance on the inside of the arm without goofing up the servo yet? I do have 1 blown one to investigate this option...not enough time, lol.

I was thinking of putting some small shims under the outer swash balls to increase servo travel closer to the middle of red in the future. But in the meantime...it seems to fly pretty good where it's at now

[beeflyer2]

I had the Mikado conversion head on my 250 with the servo balls at 10.5mm and I couldn't get the blue light at 6 degrees either. It flew horribly; very unstable, twitchy and pitchy in FF. I played with servo arms, trying to get the balls in closer, but it's not possible without binding on the cases or having the rods splayed out at extreme angles.

For the time being, I have but the flybared head back on my 250 and it's flying great!

[cudaboy_71]

the magic numbers that worked for me were 11mm on the head to ball grip and 10mm from servo center to ball on horn.

i got blue no problem with that setup. 'course i'm running the microheli head that has adjustable grips.

FWIW, while i was messing with the 3G prior to the beastx i ran into the same problem with the balls hitting the hump on the servo case. simply move the balls to the other side of the servo horn. yes, the AIL/PIT servos will be doing 'the splits', but it didnt affect flight. as for the elevator, i had to put a 3mm spacer between the servo and the frame and it was vertical again. yes, a huge PITA. but, it worked.....well, the 3G didnt work. but, the mod did.

[jaydekay]

I can't get 6 degrees either -

I am using the Align FBL head on a 250 SE. Blade grips have a distance of 11mm from the pitch control levers to center hub.
I had dead on zero degrees at mid stick.
Absolutely level swash driver arms at mid stick.
Swash driver parallel to blade grips.
Swash at approx mid travel as shown in the diagram.
Level swash (eyed it)
12.5mm radius for cyclic servos as defined in the Align Flybarless headset up

I still was not able to get a light in step J at 6 degrees.

Then after that did not work I took the suggestion of the manual which is moving the balls in.

I tried to move the balls on the servo arms inward to the next hole which puts the balls at 10mm from the center of the output shaft and still a dark light in step J at 6 degrees. I can't move them in any closer with the balls on facing inward to the frame as the Trex 250 manual suggests because they'll hit the servo. Is the only option with this setup to put the balls on the outside?

Thx.

[cudaboy_71]

Originally Posted by jaydekay

I can't get 6 degrees either -

I am using the Align FBL head on a 250 SE. Blade grips have a distance of 11mm from the pitch control levers to center hub.
I had dead on zero degrees at mid stick.
Absolutely level swash driver arms at mid stick.
Swash driver parallel to blade grips.
Swash at approx mid travel as shown in the diagram.
Level swash (eyed it)
12.5mm radius for cyclic servos as defined in the Align Flybarless headset up

I still was not able to get a light in step J at 6 degrees.

Then after that did not work I took the suggestion of the manual which is moving the balls in.

I tried to move the balls on the servo arms inward to the next hole which puts the balls at 10mm from the center of the output shaft and still a dark light in step J at 6 degrees. I can't move them in any close with the balls on facing in as the Trex 250 manual suggests. Is the only option with this setup to put the balls on the outside?

Thx.

well, i think part of the problem is trying to use the 3G manual to set up the beast. throw Align's numbers out the window.

i run 11mm from head to grip; and 10mm from servo center to horn ball.

Also, labmaster recommended aiming for 5.5° if you can't reach 6. just get it as close as possible to 6 without going over. going over is where you'll have problems.

[jaydekay]

Originally Posted by cudaboy_71

well, i think part of the problem is trying to use the 3G manual to set up the beast. throw Align's numbers out the window.

i run 11mm from head to grip; and 10mm from servo center to horn ball.

Also, labmaster recommended aiming for 5.5° if you can't reach 6. just get it as close as possible to 6 without going over. going over is where you'll have problems.

I hear you, but I had to base the head setup on something.

At any rate, I have ~11mm from the center of the main shaft to the pitch control links on the grips, and 10mm on the servos now, and still no love. What color lights do you get with these same measurements? Also are the balls on your aileron/pitch servos the longer ones with the standoffs, or the shorter balls?

Thanks

[jaydekay]

I can get purple, but just barely at 5.5* BTW

Thanks again...

[jaydekay]

I now can get mid purple at 6* with shorter balls on aileron and pitch servos, it looks like this.

[aralan]

I asked Walter about their 250 setup, and he did say he was at 10.5mm from center of servo horn screw to center of ball. He said that he didn't get a blue light until 6.5 degrees, so 6 degrees was close to blue, but not blue. With 10.5mm from servo horn screw to center of ball I couldn't get any light at all.

I'm not sure why I'm getting different results other than the different servos. He also said they had 11mm from center of blade grip to center of ball on the grip. I haven't measure mine yet, but he did say they were using the Align FBL head so I can't imagine why mine would be any different.

Now that I have the balls on the outside, I'm just barely hitting blue at 6 degrees. The 250 seems to be flying well with this setup, or at least it was until I put it in to the ground. It had nothing to do with the BeastX, I just failed to anticipate how quickly the 250 would change directions. I ended up bending one of the blade grip arms in the crash. Just got a new set today, now I have to get the head back together and put it back in the air.

Walter suggested that the HS-5045HB servos that I got with this heli (used) are probably not the best choice for flybarless. Their stall torque is only a bit over half of that of the HS-5065MGs. I'm not really sure how this deficiency will manifest itself yet. I do have some HS-5065MGs on my 450 Pro that I could pull out. I've already stolen the JR DS3500G off of the tail on it for the 250. I'm not sure how much more I want to take that thing apart though. The other option would be to get another set, but I really don't want to blow another $115 on the 250 right now.

Jaydekay, which servos do you have on there?

[jaydekay]

Originally Posted by aralan

Jaydekay, which servos do you have on there?

I'm using Hitec 65MG's which should be plenty for this system on this heli. I don't know much about the ones you have, sorry.

[aralan]

Originally Posted by jaydekay

I'm using Hitec 65MG's which should be plenty for this system on this heli. I don't know much about the ones you have, sorry.

HS-65MGs should have plenty of torque... I wonder if they'll work out the same for you as far as the geometry goes, if you move the ball to the inner-most hole and put it on the outside.

[jaydekay]

Originally Posted by aralan

I wonder if they'll work out the same for you as far as the geometry goes, if you move the ball to the inner-most hole and put it on the outside.

Perhaps. Is that a more optimal setup, Microbeast/Walter?. Meaning, angled rods VS. the setup that I've described with shorter ball links and not as far in on the servo arms (mid purple color at 6*)

Also, something that is not clear (nor clear in the manual) if we are adjusting the radius of the aileron and pitch servos, meaning moving the balls closer to the output shaft, should we also do this to the elevator servo to match the pitch/ailerons radius?

[jaydekay]

I have an idea that I might try.

What if we moved the servos inside the frame (mounting plate is inside instead of outside as it currently is) that will heli eliminate the slanted rods, and then allow us to mount the balls in the hole closest to the servo output shaft.

To me the slant of mounting the balls on the outside w/ the current servo install looks as if it could pull the links off the swash etc during flight.

[beeflyer2]

Originally Posted by jaydekay

Also, something that is not clear (nor clear in the manual) if we are adjusting the radius of the aileron and pitch servos, meaning moving the balls closer to the output shaft, should we also do this to the elevator servo to match the pitch/ailerons radius?

Yes, of course! All servos should have the same ball distance or else there will be horrible CCPM interaction.

[jaydekay]

Thats what I thought - but wasn't sure as there is some weird sh!t going on with this setup already!

Thanks.

[cudaboy_71]

Originally Posted by jaydekay

I have an idea that I might try.

What if we moved the servos inside the frame (mounting plate is inside instead of outside as it currently is) that will heli eliminate the slanted rods, and then allow us to mount the balls in the hole closest to the servo output shaft.

To me the slant of mounting the balls on the outside w/ the current servo install looks as if it could pull the links off the swash etc during flight.

it doesnt. i flew that way for a dozen flights with my 3G. but, keep tinkering. i know you'll be able to get it using stock mounting of the servos. not sure why you're having so much trouble.

[SidewaysLS4]

Might be some trouble getting them inside the frame...the main shaft bearing blocks might get in the way.