My HK500CMT build

[fourbie]

I thought I'd use this thread to ask the questions so they are all in one place as I build my HK500CMT.

It would be nice if it came with instructions but there are downloads available for the Align but even though it is like the Align there are differences or there is [ame=http://www.youtube.com/watch?v=CiV1m1OYItE] THIS [/ame]this to follow.
I think I read somewhere but can't find it now that the boom is too long on the HK500CMT and it is looking that way on my build so before I use undue force does it need to be trimmed?
In the end I cut the boom down by about 7mm. It helped taking the belt off the tail assembly. It is a pity HK don't leave the belt separate. I had lots of trouble removing the bolts holding the tube housing and one in particular gave me grief.They are M2.5x8, an odd size for my spares box.
When it came to cutting the tube fortunately I have an electric tube cutter machine which gives a nice square cut and all I had to do was remove any burrs.
Next I installed the servos as I like to get the centres sorted. There was one M2x8 bolt missing from the kit but it is so much hassle dealing with Hk it hardly warrants a mention.

Now for the next item I read about; the tail pushrod is way too long. You'd think by now that HK would have gotten these problems sorted. I cut 7mm off and threaded it.

It came with a pre-assembled head; I stripped it down and found it was dry as a bone but worse is to come. I detected a roughness in one blade grip. When I took the the thrust bearing races off, the one on that side which was rough looked like it was pitted with little bearing indents (and I thought the race washer was wrecked) but they weren't indents. Turns out it was some really hard residue. Can't believe it; only found out because I began picking at it with a screwdriver blade to see the damage and it began to come off - and it needed a lot of effort. I don't think it was hard dried grease, it looked like some sort of glue, not Loctite more like a two pack glue or a superglue, damn tough and brittle. Thank goodness dismantled it.
So now the head is on and I have added the main gear. No real problems there apart from aligning the holes for the Jesus bolt.

[Blayd]

My first 500 was the CMT. Yes, the boom was about a 3/16" too long. Otherwise the belt was way too tight.
YES, the belt will stretch ALITTLE as it breaks in, but belts shouldnt EVER be tight.
As Finless used to put it, it needs to be as loose as possible, without the belt jumping teeth on the pulleys under moderate force. In other words, loose enough to jump teeth on the pulleys if the tail hits something.. but not so that a good hard collective push will make it jump. Mine are loose enough so that if I "pinch" the belt just behind the tail drive pulley in the tail block, I can just barely touch the belts together.

Yeah, mine was too long, but not every one is...VERY easy to cut it down, some just file away at it. I believe most I've seen, were around 3/16" maybe a 1/4" needed to be cut. I used a dremel once, on another persons, I just used a hacksaw. I do recommend though, after you cut it.. take either a dremel, or sand paper, and do the edges of the cut end.

[Dylan Hudock]

I have this same things on my 500, even with 99% align parts. What I do is elongate the hole in the back of the boom that locks onto the tailcase. I use a needle file and take about 1/8 inch off.

[fourbie]

Originally Posted by Blayd

Yeah, mine was too long, but not every one is...VERY easy to cut it down, some just file away at it. I believe most I've seen, were around 3/16" maybe a 1/4" needed to be cut..

I actually took of a good ¼" - I'd worked out it was that much but when I installed it I had to pull the boom back almost that much to get the tension. Go figure. There was no way the belt was going on without removing some and I figured it is better to take of a mm too much than a mm too little. Main thing was that I wanted to know if that's what I had to do so thanks.

Originally Posted by Dylan Hudock

I have this same things on my 500, even with 99% align parts. What I do is elongate the hole in the back of the boom that locks onto the tailcase. I use a needle file and take about 1/8 inch off.

I don't see how that would work as the boom goes to a stopper ridge in the tailcase doesn't it? I had thought of elongating the slot on the end that goes into the frame's boom mount but I preferred the easy chop approach.

[fourbie]

Originally Posted by Dylan Hudock

I have this same things on my 500, even with 99% align parts. What I do is elongate the hole in the back of the boom that locks onto the tailcase. I use a needle file and take about 1/8 inch off.

I am now building a 500GT and the difference is phenomenal. The tailcase went straight on and the belt fitted just right.

I'm buiding this one cos I broke the CMT. Never even flew it. To cut a long story short
on the first trial something felt wrong. I put a rate gyro on and things seemed well but then the tail housing twisted round; it would have gone more but the tail pushrod held it at about 40 odd degrees.

There is a hole in the boom. I now know the regular tail assembly has a lug in it that fits into it. However this has a metal tail and the tail housing has a hole in it but on the opposite side to the hole in the boom I decided to turn the tail housing over and then where the holes lined up I put in an M4 button head through from inside the tube. The housing was symmetrical so turning it through 180° was easy enough. It worked well too.

But then the screws for heli's the tail fin were on the other side. The tail fin was on the same side as the tail blades........I thought it would be OK but it was a mistake. I spooled it up and things were going well, throttled it up but it suddenly span around and the fin caught in the ground, broke, bent and then caught one of the tail blades.
End result, bent tail shaft, teeth gone from the tail drive gear assembly, tail blade gone. Also, it seems that the tail belt auto rotation gear was not properly engaging the tail drive gear. That gear was well wobbly too. The gear is flat but the centre shaft drilling off vertical. Maybe I missed something but you'd think the mesh would be adjustable.
The moral, the upgrades version was not worth it.

[Gladius]

Originally Posted by fourbie

The moral, the upgrades version was not worth it.

Thats a lesson that most of us have to learn the expensive way!

[Dylan Hudock]

Originally Posted by fourbie

I actually took of a good ¼" - I'd worked out it was that much but when I installed it I had to pull the boom back almost that much to get the tension. Go figure. There was no way the belt was going on without removing some and I figured it is better to take of a mm too much than a mm too little. Main thing was that I wanted to know if that's what I had to do so thanks.



I don't see how that would work as the boom goes to a stopper ridge in the tailcase doesn't it? I had thought of elongating the slot on the end that goes into the frame's boom mount but I preferred the easy chop approach.

Oohh yeah, sorry about that! I didn't think about that! my 500 has the metal one piece silver and black tail case, and the boom slides in and the pin is what stops it.

[fourbie]

Originally Posted by Dylan Hudock

my 500 has the metal one piece silver and black tail case, and the boom slides in and the pin is what stops it.

The CMT has a one piece alloy tailcase but no way of stopping it from rotating while the GT has a lug that locates in the hole at the tail end of the boom.

[Dylan Hudock]

https://tmkarc1hobby.com/tarot-500-m...fytl50073.html This is what I use. Very good quality and has the pin to hold it to the boom on the fin mount. The tail boom can slide in and out without stops but the pin locks it in place.

[stingeragent]

Ouch man. What made you decide to go with the 500 cmt? I had possibly the worst experience of my hobby life with that heli. I spent close to 1300 total over the course of like 4 months, and got like 3 successful flights out of it. Hope you have better luck than I. When it was all said and done, I had an align FBL head, align tail case, align pro grips, align servos, bascially the whole thing was align except the battery tray and frames. You were wise going belt. The HK tt bearings are terrible. Vibrations like none other. Had about 6 crashes with it and several hundred worth of torque tubes, and torque tube gears, and blades later I switched it to belt and still had issues.... bad bad memories on that bird

[fourbie]

Originally Posted by stingeragent

Ouch man. What made you decide to go with the 500 cmt?

It was the extra for a few quid more that made me go for it but now I compare it to the GT I can see that the extras just don't work, well the tailcase doesn't at least.

I have to admit I get a weird pleasure out of fettling something to make it fit/work which is why I am persevering.
One thing it has told me is that the HK550GT might be worth a try if I get this GT flying OK.

[fourbie]

Back to the GT build..............is this amount of (vertical) engagement good for the auto gear to the belt pulley gear? It is an awful picture but the best I could get. Again - no adjustment unless I am missing something.

[Gladius]

Your auto-rotation gear looks like it is sitting too low. There's almost no room between it and the frame. Is there a spacer between it and the main gear? Could you find a different spacer to use?

[fourbie]

Originally Posted by Gladius

Your auto-rotation gear looks like it is sitting too low. There's almost no room between it and the frame. Is there a spacer between it and the main gear? Could you find a different spacer to use?

Yes there is a washer but the low sitting is determined by the height of the bush that the two gears are on (one way bearing etc) . The bush sits under the mainshaft lower bearing and is drilled for the jesus bolt so where the hole ison the bush that's where the gear is. If I take out the spacer the main gear then can down and up on the bush.


Also, the gear assembly is a damn tight fit in the frame. Fortunately the auto gear is not warped like the CMT one was (it had a 2mm drop!).

So TBH I cannot raise the auto gear up the mainshaft; it would only take a mm too. I suppose the tail gear will run OK as there is 90% contact to the auto gear.

One solution would be to shave a mm off the top off the bush but I'd probably wreck the squareness then.

[fourbie]

Originally Posted by Gladius

Your auto-rotation gear looks like it is sitting too low. There's almost no room between it and the frame. Is there a spacer between it and the main gear? Could you find a different spacer to use?

I've compared the GT against the CMT from the mainshaft lock collar down.
The one way bearing shaft is the same in both to 0.3mm. So in theory that is not what is pushing the main drive gear set lower.
I checked the distance between the mainshaft bearing blocks and they are about 1.5mm farther apart on the GT frame than the CMT. The lower one is 1.5mm lower. This means the main drive gear set is lower in the frame measured from the head assembly.

I can't see what I can do about it - I'll just have to live with it.

[fourbie]

I decided not to live with it.
Here in the first pic you can see what I had to deal with - the OWB bit.
I chucked it up in the lathe and took off just over 1mm from the face and re-profiled the chamfer.
I am not sure if the two pics show the difference and I'll add one later of the new position the gear set takes in relation to the motor and tail belt pinions. Basically the mainshaft is now 1.4mm higher.

[Gladius]

Don't forget to lengthen your servo to swash links to keep your head geometry the same.

[sharicasmi]

I just thought I should mention, I've been noticing my mostly Alignized HK 500 CMT has been burning through front end TT gears the last couple days. I take a close look at the mesh between the tail drive gear and the first TT gear, and it's really loose.

Anyone who owns an HK 500 CMT/GT check the mesh between your first tail drive gear and your second tail drive gear. To make the TT gears mesh properly, I had to file down the 10 holes in the frame where it connects to the tail unit. Seems to work great now.

[stingeragent]

I was interested in the 550 despite my 500cmt probs. However the cheapest I could build it would be 450-500 and thats flybarred version with all sketchy electronics. Im good with the yep esc but hk servos are hit and miss. That and the flybar version has belt so u gotta scrap around for compatible parts since align 550 was always TT. To me its just not worth it. Id rather spend the extra 300 and get the align 550

[fourbie]

Originally Posted by Gladius

Don't forget to lengthen your servo to swash links to keep your head geometry the same.

Yes thanks, I had done that. Surprisingly, it actually didn't take much.

I was surprised to find how far out the CoG was on the blades. The weight was bang on equal and I wasn't expecting the CoG to be out as much as it was.