HK 450 MT build Thread.

[vinay]

Graphical representation here.

http://www.rcgroups.com/forums/showpost.php?p=14398634&postcount=12133

[vinay]

Tomorrow

[anwar]

Not sure if slipping-tight is ok though, Anwar would comment on that.

Slipping at the addition of a small amount of force seems a bit on the "too loose" end.  The way I was doing it was to apply a medium level of pressure and get one side of the belt to go  half way towards the side (when the belt is mounted and show up as two parallel lines).  This is similar to the illustration in your post above. 

Like Rajesh mentioned in my earlier posting of the same information, it is the amount of pressure that is very subjective from person to person.  So the simplest is a "not too tight, not too loose" explanation.

[vinay]

Anyways, I will understand that well when I reach jakkur tomorrow. certain things like/pressure feel can only be touched/felt. Thats where the real flyers come in, when they explain standing next to me.

[vinay]

Updating image here.

[vinay]

Had been to jakkur yesterday. Luckily Rajesh was there to help me out and there were Tons of problems.

First of all the blades were not tracking. We changed many settings/Blades only to realise that the feathering shaft might be bent in the previous shaft

Also the tail heli was turning clockwise requiring constant left rudder inputs, and when suddenly raised the heli was turning anti clock wise. Rajesh trimmed it for me. I took the control of the TX. Guess what, I was dumb stuck, The Heli started moving away from me and my fingers are not moving at all. All the sim practice didn't even kick in to make me come back into my senses.  I gave the TX to Rajesh and he started getting it back to us and as bad luck would have it, the ESC started cutting of the battery due to low voltage. Luckily Rajesh's quickness helped land the Heli in 1 piece.

Posted a few questions on RCGroups as the majority of the HK Gyro Users are there.

Got back the answers saying that the head speed was not even reaching 1600 at my settings, where it was supposed to reach 2500 minimum, before the pitch curve should kick in , this was causing the causing the heli turn Anti Clockwise when suddenly pitched up. This also explains why the battery lasted for 4 mins when it was supposed to last 9 mins. The slow head speed and the heavy pitch required to take the Heli off was screwing up the efficiency by 50%

Also got back responses saying that I need to Trim the Heli in rate mode, moving the Servo manually (as suggested by Anwar long back here), and then switch the gyro switch rapidly thrice, to get a good head lock.

I still have a feeling that Gyro was damaged in the previous crash, let me mount another  Gyro and see how that ones behaves.

Thanks to Rajesh, I learnt a Hell lot of tips from him and saved my Heli finally. Lots of work on the Heli, and I will do it some time later this week.

[anwar]

Posted a few questions on RCGroups as the majority of the HK Gyro Users are there.

The HK 401B is claimed to be a direct/true knock-off of the Futaba GY401, and the claim is that the setup and performance is similar.

If you did not have enough headspeed, the heli would show a slow nose to tail rocking motion while hovering (like the head would dip a bit and the tail would be higher than the head, then the tail would dip and the head would be higher than the tail, so the rocking is on an axis perpendicular to the ground).  This is the classic indication of lack of headspeed. 

And this is in contrast with other gyro issues (like incorrect gain) where the tail wags or drifts in an axis that is parallel to the ground.

[RotorZone]

There wasn't any significant wobbling to indicate a low head speed. But the gyro was drifting and never wagged even after going to full gain which also could indicate low head speed. Anyway before I even looked at them I wanted to get the blades to track decently. Changing the link length was giving inconsistent results, could be the feathering shaft as Vinay said he didn't check it after his crash.

There was another thing that got me thinking. Does the orientation of the gyro installation matter ?    To make it more clear, the gyro is installed on a plane perpendicular to the main shaft. Can it be rotated to any position on this plane ? Some installations I have seen indicates that it does work. From an engineer's perspective, it does take a sensor capable of sensing two axis and a software that has to find the resultant vector from the two axis. Could be that all gyros do this, I just never thought about it.

[anwar]

True, I should have clarified that the "nose to tail" wobbling happens in a particular range of "not enough" throttle (main blade rpm).  If the head speed is even below that, the symptoms you saw would be more prevalent.

Some blades are warped, and it is hard to get good tracking on them (especially after crashes).

Never saw any proof so far that the orientation of the gyro (within the axis it is compensating for) making any difference in gyro performance. I have seen people mount it religiously at a 45degree angle (in the same axis), but I never felt the need to try it.

[anwar]

A quick search does bring this up though, where it is suggested that rotating it by 90degrees is one thing to try if there is drift in HH mode.

http://www.futaba-rc.com/faq/faq-gyros-q1122.html

Wonder if it is more a trick to compensate for design/performance issues, and whether this is model specific  

[vinay]

Anwar, Id did not make much diff I belive after the orientation change of the Gyro, though I am not sure as I did not fly the Heli. Also it is true that some blades are warped. we changed the blades and the off tracking reduced almost by 60 to 70 percent.

[anwar]

When it comes to gyro mounting, I always felt that the foam padding is more important in gyro performance as compared to orientation.

[vinay]

Well, I used the ones that came with the Heli, it was a good one, and everybody seems to be using the same pad on their Helis, never came across a thread where people are complaining about it.

[anwar]

It is not about using a particular brand of padding etc.  It is more about the impact of proper padding on gyro performance. It certainly is one of the things to look to, when you are running out of options for gyro tuning.

[vinay]

What do you expect me to do, I have this padding also with me

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idproduct=8999

Make it double layered and use it?

[anwar]

I don't think you have run out of options in terms of gyro tuning, right ?  

Just do the rate mode setup first, and then switch to HH. It is very very rare that you have to look at padding issues etc.

[gauravag]

Does the steel plate between the 2 layers of foam make a big difference ? I see that on all other gyros, but i guess you are not using that. Maybe the steel plate prevents some vibration from creeping up to the gyro ?

[vinay]

Anwar, is this the tail belt for TREX/HK450? its 397T

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280438580042&ssPageName=STRK:MEWAX:IT#ht_1779wt_939

[vinay]

Ya confirmed here, its the same

http://www.helidirect.com/align-drive-beltxl-397-mxl-ht1003-fits-450-p-192.hdx

[anwar]

Does the steel plate between the 2 layers of foam make a big difference ? I see that on all other gyros, but i guess you are not using that. Maybe the steel plate prevents some vibration from creeping up to the gyro ?

I am afraid we are going on a tangent with this  

Usually what ships with the gyro is the obvious/best choice, as the manufacturer has confirmed that it works great for THAT gyro.  What I was suggesting is that when you have unexplained tail issues even after ensuring the basic setup, then one of the things you have to look at is how the gyro is mounted. And at this point, I found that the orientation (in the same axis) was not significant, but the foam/pad used for mounting of the gyro has a good impact on performance.

[gauravag]

BTW the gyro HK 401 does NOT come with any sort of padding or steel plate or anything to attach it to the helicopter. You are supposed to devise your own ways...

[vinay]

But the Heli comes with one But its not suggested to reuse it.

[RotorZone]

I doubt the drift was due to vibration as the drift was significant. If not corrected, it would have done a full piro in under 10s. It was as if it was not detecting the center correctly. One thing I forgot totally about was to reset the center. In a Futaba 401, 3 quick full deflections of the rudder stick to either side will reset the gyro. Should have tried this to see if the drift goes away. Same could be achieved by toggling between rate and HH mode 3 times. HK gyro might have the same feature.

[vinay]

Rajesh,

I tried yesterday night and 3 flips of the gyro switch and the center was detecting properly with blinking light-and a steady glow. But I will bring additional gyro next time so we can fix in 15 mins any problems.

[anwar]

Never had to do that (3 flicks to ensure centering) on original Futaba 401s, because I always tend to setup in rate mode first. In rate mote, the centering is always there, and the 3 flick trick is needed if you are doing setup in HH mode.

But in your case, it looks the rate mode setup was never done, OR was it done yesterday on the field and you still had issues ?

PS: I have mentioned this "centering of servo in HH mode by flicking the sticks" here : http://www.rcindia.org/helis/hk-450-mt-build-thread/msg12947/#msg12947