HK250GT Science Experiment...

[ToddMcF2002]

I'm sure they make process changes often. Their goal was to be compact, looks like they have made some progress.

[mike_drz]

looks really pro, you're really paying attention to detail. I've seen a lot of different servos and fbl systems though. Which ones did you settle on?

[ToddMcF2002]

Originally Posted by mike_drz

looks really pro, you're really paying attention to detail. I've seen a lot of different servos and fbl systems though. Which ones did you settle on?

Yeah sorry I've been gathering lots of stuff, much if it I won't use on this project. But I have (2) of these clones now and I'll configure them like this:

HK250GT (CopterX FBL Head):
KBar
DS76 Cyclic
DS76T on Tail
Talon 15
Turnigy 250 Series 3600KV

CopterX CX250 (FBL)
HobbyMate HB800 decased
same as above otherwise

The DS76's are high resolution, fast and incredibly light. They are however easy to damage. Nothing is perfect. I have been gathering them from used sources and I now have 9 of them. 2 of them were from my own 300's.

The original Turnigy servos I picked will do duty on my 300 CFX's. The white ones who knows.

[mike_drz]

The above looks good. Are the white ones the A version of the original HK servo?

[ToddMcF2002]

Mike - I don't know. How can I ID them?

Quick Update:

I cleared a bunch of other RC projects out off my queue so I could get back to the 250's. While I was off building FPV quads, finishing my 450 build and repairing wounded micros a bunch of used DS76's came in. I've been collecting them from other freaks.

I have a bit of experience with these little horrors and besides gears stripping the servo tabs like to crumble apart. I had the same problem with DS76T's on my 130's so I decided to reinforce the tabs preemptively. I used cut to size plastic from a AA battery box and 6 minute two part Epoxy. Once the epoxy cures you can just dremel out the original hole and grind off the excess. I posted pics of 3 servos in progression (left to right: no reinforcement; plastic tab laminated with epoxy; dremeled tab). The last pic shows the new overall servo tab thickness.

One important note - for the elevator servo I'm going to have to dremel down the laminated servo tab to just a very thin supporting layer. If I don't it will slightly throw off the geometry. The Aileron/Pitch servos are mounted facing outward so the original tab face is against the frame. There are no geometry changes for Aileron/Pitch. The Elevator servo however is mounted inward, so the added laminate thickness will offset the horn position. If anyone uses this method simply put the laminate on the other side of the original tab for the elevator servo. Problem solved.







Speaking of geometry, I really start to wonder about the Trex 250 engineers. I've seen some really messed up 250's in person. Ones with linkage rods at odd angles leaving no hope of maintaining a level swash during combined pitch movements. The linkage rods have to be pretty close to parallel to the frame sides in all profiles. Your swash cannot hope to raise and lower linearly at all with swashplate linkage rods otherwise. Well... unless they are all equally f-ed up at exactly the same angle. Needless to say its much better to simply shoot for strait!

To make a long story short these are the extended servo horn balls needed to achieve parallel using the DS76's on pitch and aileron. Probably other brand servo's as well. Elevator doesn't need a geometry adjustment so the stock HK250GT servo horn balls can be used.

[mike_drz]

Ive got too many projects with the foamies and balsa build too. Its becoming a full time job instead of a hobby haha.

I think finless bob had a video on the strange geometry of some of the align models. I don't recall his explaination or if he changed it though.

[ToddMcF2002]

I test fitted everything before starting the laminate work and the geometry is pretty good. I'll tell you, I'm trying to take my time with these projects but I cannot wait to get these 250's in the air!

[mike_drz]

I'm the same way. I try to take my time. It's always on the back of your mind nagging you to get it done and flying asap.

[rodo1268]

I'm amazed at the similar paths we took, I went through my 250 phase about a year ago and ended up with three of the dang things. Ea with different fbl units, servos, esc's and motors.
Tarot zyx-s, zyx-s2, yellow kbar, scorpion, align bl250, viper, cc15, yep15 (x2), hobbyking cheapo servos, eflite76,76t's, mks 95i, ds410's etc etc..
The best flying setup I had was the yellowk with the cc15, ds76 &76t with the align motor.
Gosh I was obsessed with these little suckers, lots and lots of fun.
But for me it was like boat ownership, best 2 days are the day ya buy & the day you sell!

Nice work btw!

[ToddMcF2002]

The 250 is tinkers paradise I guess. Align has nearly abandoned the poor thing from a product development perspective but it is such an easy platform to support.

• The used market is literally flooded with 250's, both DFC and flybarred (belts!) are out there aplenty.
• Align and clone companies are still making parts including flybarless heads and motors.
• The 250 essentially uses 450 electronics so nothing 250 specific to worry about.
• FBL units are getting smaller and lighter because of the v120D02s and Blade 180x.
• We can trust Horizon to pump out crappy little plastic servos for years to come

It sure would be much easier for me to just go fly my 180 but I just can't put down these 250's

[Slobberdog]

Spent the last couple of weeks getting the excess fat of my 250 dfc, dos I was looking at this thread, have now got mine down to 306g with the heavy batteries and sub 300 with the lighter compacts that I had under warranty,

You are right, tinkers paradise, and tbh I'm the perfect sucker for it, I went sort of along your line, ds76's and ds76t, plastic canopy as it stretches better over the batteries and it is light, and the vx1n and sat, both cased and only 14.5g

But I love the way this little bird flies now,

[myxiplx]

I agree, we're all tinkerers here :-)

I've got a bunch of 250 spare parts after an early crash which was cheaper to buy a second hand 250 than the parts! And I'm eying up the CopterX 250 now, its a great cheap airframe to throw everything in, and I'd be gutted if my 250 was ever down.

[Murph_d]

I have a bit of experience with these little horrors and besides gears stripping the servo tabs like to crumble apart.

You can get these servo tab savers from Dylan.
http://http://astroid-designs.myshopify.com/collections/all?page=3

I usually use spare washers from old feathering shafts.

I built my copterx 250 in parallel with my trex 250. As it goes, the copterx eventually became mostly Align. I can hardly tell the difference between them. One interesting thing, the copterx build is about 10 grams lighter (287g vs 297g AUW). I never weighed the frames but since the two helis are identical otherwise, it has to be the frame.

[ToddMcF2002]

The carbon fiber itself is quite a bit thinner than Align. Not 10g's but it is thinner. Should not be a problem though.

[nighttrain06]

Originally Posted by Murph_d

You can get these servo tab savers from Dylan.
http://http://astroid-designs.myshopify.com/collections/all?page=3

I usually use spare washers from old feathering shafts.

I built my copterx 250 in parallel with my trex 250. As it goes, the copterx eventually became mostly Align. I can hardly tell the difference between them. One interesting thing, the copterx build is about 10 grams lighter (287g vs 297g AUW). I never weighed the frames but since the two helis are identical otherwise, it has to be the frame.

Mmmm? I may need to pick up some of those tabs! Have a brand new 76T laying in my parts supply, I run the Futaba S3157 on my tail, Spartan Quark gyro, Turnigy 10MG cyclic servos,
Xtreme Production 210 CF blades flies like a Dragon fly!

[ToddMcF2002]

I don't see the benefit of the carbon fiber tabs. The Epoxy adds the structure and keeps the brittle plastic together. Using a rigid CF tab to support a terriblly brittle plastic won't keep it from falling apart. You need the 2 part epoxy to plasticize the structure.

[ToddMcF2002]

Hmmm... either I made a noob error or the factory did. My main blades are free wheeling clockwise instead of counter clockwise like very other heli I own. Thing is I don't remember taking out the one way bearing? I must have though. So just to confirm, the blades *should* freewheel on the 250 counter clockwise? It would fly as is because the head will turn if the gear is turned clockwise, just not by the head....

Maybe I drank too much that night...

[nighttrain06]

Originally Posted by ToddMcF2002

I don't see the benefit of the carbon fiber tabs. The Epoxy adds the structure and keeps the brittle plastic together. Using a rigid CF tab to support a terriblly brittle plastic won't keep it from falling apart. You need the 2 part epoxy to plasticize the structure.

Myself that is just what I was thinking....along with the CF tabs epoxied to the servo tabs...
I had that issue with a tail servo that I used with one of my Blade SR's that I converted to belt drive....had a Corona 919MG that cracked the ear mounts...used a little thin piece of plastic, and JB weld formed over it worked like a champ!

[nighttrain06]

Originally Posted by ToddMcF2002

Hmmm... either I made a noob error or the factory did. My main blades are free wheeling clockwise instead of counter clockwise like very other heli I own. Thing is I don't remember taking out the one way bearing? I must have though. So just to confirm, the blades *should* freewheel on the 250 counter clockwise? It would fly as is because the head will turn if the gear is turned clockwise, just not by the head....

Maybe I drank too much that night...

Now I'm confused, my blades don't free wheel either way....the motor, tail blades both turn in either direction.....

[mba83]

The OWB lets the blades spin clockwise freely (w/o spinning the motor). Spinning the main blades counter-clockwise will lock the OWB and spin the motor also. It's like that on most RC helicopters.