TREX250 Tail analysis, spacer upgrade and Chinese weights

[HEIM JOINT]

These are videos of :

• Diagnosing the tail bind problem.
• A bearing spacer upgrade.
• Chinese weight testing

Diagnosing the tail bind problem.
I had this tail assembly to design the chinese weights for the T250. But first I had to get the tail assembly to work smoothly enough to do the testing.
I am not bashing Align!!! The things that you see in the video are problably not typical. this was probably a bad tail. This video is just to help those who might not know how to diagnose a mechanical problem. These are areas to look at to find causes of excessive drag. Your tail may have none of the issues seen in these videos.

TAIL BINDING PART 1

T250 TAIL BINDING ANALYSIS PART 1.wmv (7 min 11 sec)

TAIL BINDING PART 2

T250 TAIL BINDING ANALYSIS PART 2.wmv (6 min 6 sec)

Comments:

• On this tail, just replacing the blade grip bearings was 90% of the cure.
• The spacer upgrade (video below) eliminated the severe slop in the blade grips. I think the angle that the blade grip moved to under load caused binding of the link and bushing on the blade grip.
• The pushod forces of 10-12 oz. seen at the end are typical of a 200 size heli (Identical to a gaui 200)
• I think the high blade grip slop may allow the grip to rub or bind on the hub under load on some helis.
• The axial clearance gap between the hub and the blade grip was only .002" on the tail I had. That would explain why Bert's longer bolt fix worked on some helis. This is probably addressed by Aligns replacement hub.

Bearing spacer upgrade and Chinese weight test



These are videos of:

• Why a spacer decreases the bearing loads
• What exactly is bearing preload
• Can Chinese weights help the T250

I designed the bearing spacer upgrade to allow the slop to be adjusted out like a Kasama grip. This was necessary to get the tail I had to behave. This also reduces the loads on the bearings from moment loads (bending) by over half. (Note: this does nothing for the centrifugal loads on the bearings, they remain unchanged) The Chinese weights are the same as all the others just scaled down for the T250

SPACER UPGRADE & CHINESE WEIGHT PART 1

TREX 250 TAIL BLADE GRIP UPGRADE & CHINESE WEIGHT PART 1 (9 min 17 sec)

SPACER UPGRADE & CHINESE WEIGHT PART 2

TREX 250 TAIL BLADE GRIP UPGRADE & CHINESE WEIGHT PART 2 (9 min 38 sec)

Comments:

• I dont think any single bearing blade grip setup will will perform as good as two bearings preloded with spacers.
• You will need to trim the tail blade to clear the longer blade grip screw (see picture)
• Chinese weights will not cure a binding tail problem!!!!!!!!!!!!!! They will only improve a properly functioning tail.
• The Chinese weights are tuned for the curved "batman" blade. They will work with the straight blade but the pushrod forces will be higher (about 5 oz.)
• The Chinese weights reduce the pushrod force to 1/10th of original.
• The Chinese weight nut is self locking to allow you to fly immediately (still use loctite)
• The Chinese weight sets are matched to within 0.002g to minimize any balance problems

Both the Bearing spacer upgrade kit and the Chinese weights will be available in 1-2 weeks. I will post in this thread when they are available with more information.

PLEASE DONT PM ME OR INQUIRE IN THIS THREAD UNTIL I POST THAT THEY ARE READY!!!!!!
IT MAKES DOUBLE WORK FOR ME TO ANSWER PMS INQUIRING BEFORE I HAVE THEM AVAILABLE.

Thanks for your patience in advance,

HEIM JOINT

[12/07/41]

HEIM JOINT
thanks for all your time and work on this!

[s76 mech]

Yup thanks, that looks so cool, add me to that list!

[DesertClimber]

I watched your vids last night. Good stuff!

[NotEnoughTime]

Heim Joint,

You are undoubtedly The Man! From the time you spend to make these mods, to the time spent in explanation of theory in all you do. You and Finless are top notch examples of knowledge applied in our sport. I commend you for all you do and look forward to future advancements that you will surely take part in.

[Gutaaaooo]

Can I get on a preoder list? I want these BAAAADDDD. They do wonders on my T450, and t500. TKS MAN!!! YOU ARE GREAT!

[heli-on]

Awesome job throwing these vids together, let alone the in depth detail you go into.

I was skeptical about the effectiveness of chinese weights on a model this small. You totally blew my theory out of the water.

I was wondering if your only reason for placing the bearings in the polarity you chose was to cup the grease (as was explained in the video). It seemed to be that when simulating a load on the bearing (pressing the stack towards the head of the bolt), action seemed smoother with the open end facing the bolt head (which forces the bearings into their races). Do the bearings have polarity or are they just as effective in either orientation?

Please put me in the queue for the bearing and chinese weight mods. Again, nice work and thanks for taking the time to put together undisputable evidence of your findings.

[teshreve]

Just watched all 4 videos. Very nice work. Really, exceptionally well done.
In one of your other videos, you mentioned it was probably a good idea to keep trivial forces on the servo with any "chinese" weighting, instead of a true zero load. I tend to agree as any servo gear lash, linkage slop, etc would only be felt at the transition from/to 0 pitch (instead of throughout the range). In this video the weights pretty much show zero forces until the end (and may even go negative?).
The sheer size of the weights in relation to the grips is pretty amazing.

Thanks for the info!

[HEIM JOINT]

Originally Posted by heli-on

I was wondering if your only reason for placing the bearings in the polarity you chose was to cup the grease (as was explained in the video). It seemed to be that when simulating a load on the bearing (pressing the stack towards the head of the bolt), action seemed smoother with the open end facing the bolt head (which forces the bearings into their races). Do the bearings have polarity or are they just as effective in either orientation?

A Standard radial bearing has no direction. Its thrust capacity is the same either direction. On larger bearings the ball cage or retainer is symetrical and the direction to cup the grease would not apply. On these very small bearings the ball cage is not symetrical and does have a "cup" direction. On some of these blade grip bearings that I have seen that I would consider poor quality, it looks like the retainer may stick outside the bearing faces under axial load and might rub whatever is next to the inner race. This may be part of the "binding problem" since just changing to another bearing set removed 90% of the drag.

HEIM JOINT

[blade strike]

SOB.... I'm sold!!! Great work man and sign me up for a kit when ready!!!!

[Finless]

Nice HEIM JOINT! My my hand force testing Saturday the forces were huge! I showed this to many people including Andy. It's almost hard to believe a little servo can handle these forces as they are larger then any other heli I have seen! I could almost not move the slider to full deflection by hand without the control rod bending and twisting the rod guide on the boom!

Can I get a couple of sets of these when they are ready for a review?

Bert Kammerer, Andy told me you had made this mod to yours? What was your conclusion?

Thanks,
Bob

[Bert Kammerer]

I actually got a chance to fly HEIM JOINT's Chinese weights for the 250 along with his tail mod. I have only tried them with the Spartan gyro and several different servos, but so far I haven't been able to tell a difference in flight performance. However, there is absolutely no doubt in the fact that this is a must do mod in order to extend the life of a servo. While testing this with a Futaba 3154, I noticed the servo temps around 120 or so after a 4 minute flight and with the weights, the temp dropped to below 100 degrees!

[Aberdeen]

Originally Posted by Bert Kammerer

However, there is absolutely no doubt in the fact that this is a must do mod in order to extend the life of a servo. While testing this with a Futaba 3154, I noticed the servo temps around 120 or so after a 4 minute flight and with the weights, the temp dropped to below 100 degrees!

Plus...I bet without the added resistance you get 100% of the speed rating of a given servo, extracting all the performance from your choice of gyro.

[HEIM JOINT]

Originally Posted by teshreve

Just watched all 4 videos. Very nice work. Really, exceptionally well done.
In one of your other videos, you mentioned it was probably a good idea to keep trivial forces on the servo with any "chinese" weighting, instead of a true zero load. I tend to agree as any servo gear lash, linkage slop, etc would only be felt at the transition from/to 0 pitch (instead of throughout the range). In this video the weights pretty much show zero forces until the end (and may even go negative?).
The sheer size of the weights in relation to the grips is pretty amazing.

Thanks for the info!

I now am tuning to have what I consider "neutral response" meaning the force to move from 0 pitch to 20 degrees is aproximately the same as the force to return to zero pitch. Since it takes a certain amount of torque to overcome the bearing drag. The forces seen at the pushrod are a combination of tennis raquet effect, drag torque and any aerodynamic forces. By tuning the weights to give neutral response I think I am most accurately taking the tennis raquet effect to zero. From all the responses I have seen this is working well. I think that since the servo can move with almost no effort. The gyro can compensate for any play in the tail system dynamically

HEIM JOINT

[HEIM JOINT]

Originally Posted by Finless

Nice HEIM JOINT! My my hand force testing Saturday the forces were huge! I showed this to many people including Andy. It's almost hard to believe a little servo can handle these forces as they are larger then any other heli I have seen! I could almost not move the slider to full deflection by hand without the control rod bending and twisting the rod guide on the boom!

Can I get a couple of sets of these when they are ready for a review?

Bert Kammerer, Andy told me you had made this mod to yours? What was your conclusion?

Thanks,
Bob

Bob,

You will have them as soon as they are ready. From what I experienced you will need new (not Align) blade grip bearings to get rid of the problem. The spacer upgrade alone did not change it until I put new bearings in.

Thanks for all your help Robin

[ndoren]

Agreed, the Align 1.2mm bearings are pretty crappy. You'll probably push the inner race right out of the bearings while preloading. I did my own version of Heim's preload with better bearings, and the results were spectacular. I can't "wait for the weights." Align's new tail hub mod with the single 2mm bearing isn't going to do you a favor if you want the Chinese weights. Those weights will put too much side (lateral) load on that bearing, given the centripetal force pulling on them at high throttle. It's gonna take a good set of 1.2mm bearings with a proper preload to handle the lateral load. It's all going to be worth it in the end. Neall

[DesertClimber]

Originally Posted by ndoren

I can't "wait for the weights."

You are just FULL of pun tonight!

I ended up going with a hybrid of (two) 2mm bearings per grip like "Arky" said he was doing.

It's very nice. No slop in/out or laterally, and smooth like silk.

[Finless]

Heim Joint, been thinking about this on the T250. I think it might be better to tune the weights so there is some tennis racket effect trying to return the slider to center. Reason I say that is slop. By having some return force this "takes up" the slop that is in the slider. Of course when you transition from left to right it will slop over and take up the slop the other direction. But with ot without the mod this will be the case anyway.
With 0 force then the tail as the ability to always slop back and forth in any position and thus the servo is wagging trying to compensate and take up the slop.

All my align helis the design has some inherent slop in the slider. On larger helis the proportions are enough that the slop doesn't seem to cause issue. But when they scaled down the 250 the didn't scale down the part tolerances (and probably couldn't or it would be too expensive) so now in proportion the slop is too much for this little tail and the control resolution. So having a small amount of back force may help keep this slop taken up. Get the idea?

Bob

[HEIM JOINT]

Originally Posted by Finless

Heim Joint, been thinking about this on the T250. I think it might be better to tune the weights so there is some tennis racket effect trying to return the slider to center. Reason I say that is slop. By having some return force this "takes up" the slop that is in the slider. Of course when you transition from left to right it will slop over and take up the slop the other direction. But with ot without the mod this will be the case anyway.
With 0 force then the tail as the ability to always slop back and forth in any position and thus the servo is wagging trying to compensate and take up the slop.

All my align helis the design has some inherent slop in the slider. On larger helis the proportions are enough that the slop doesn't seem to cause issue. But when they scaled down the 250 the didn't scale down the part tolerances (and probably couldn't or it would be too expensive) so now in proportion the slop is too much for this little tail and the control resolution. So having a small amount of back force may help keep this slop taken up. Get the idea?

Bob

Bob,

I understand completely and I will check it out on the next tuning run. My initial guess is the tuning that would give a pushrod force that will actualy gently push back to 0 pitch from either side would be relatively high. probably 5-6 oz. on the T250. You can see if there is a performance difference by comparing the batman blade to the straight blade on the T250 with the Chinese weights on. The straight blade is wider and has about 5 oz, pushrod force using the weights that were tuned for the batman blades. If the tail seems more precise with the straight blade then that would support your point. You would need to separate more "authority feel" from more "precise feel" because the straight blade has more area. I would think that if this was a large issue you would see a "micro wag" in a hover from the gyro/servo fighting the play in the control system.

Robin

[steves]

Can anyone tell me where we can buy your chinese mod kits?
Thx