Flybarless Conversion

Regular follows of this blog will remember that I mentioned the flybarless conversion kit for the T-Rex 250 a few months back. Well it never really left my head but I didn’t want to learn the intricacies of it with a 250 so I never really considered it. So when it came to buying the T-Rex 550 I knew I had to go for the flybarless system. It’s big, so easy to sort, and lots of people are using it so there is plenty of help out there. Now I have it working and running on the 550 (which is awesome) and Fast Lad suddenly put it in the sale section, it was really a forgone conclusion.

T-Rex 250 Pre Strip Down

I’m not expecting this to be easy, the 250 is twitchy and the 3G requires a prefect set up but if any heli needs it then the 250 it is. There is so much slop in the flybar cage that to get rid of that seem obvious.

The picture (left) shows the heli before work commenced, all ready on the bench with the 3G box there too. I have to say it’s very cute being that small.

T Rex 250 - Stage 1 - Strip down

Stage 1 – The first bit was to strip the heli down. One of the jobs I meant to do before was to replace the motor pinion. In June I changed the motor for a Hyperion one but the standard pinion didn’t really fit and I had to epoxy it.  Therefore I got a 15T pinion with a grub screw in it. (see here)

Stage 1 - Strip down and Motor with new pinion.

It is worth noting that I had to Dremel the end of the grub screw off so it would rotate within the motor mount. Part of the strip down involved changing some worn components not really worth mentioning here but stuff that had worn out along the way.

Stage 2 – consisted of fitting out the heli with the 3G unit box and the rest of the electronics that all had to be changed to accommodate it. This part can take some imagination to get correct as there is a lot of wiring within a small heli.

T Rex 250 - Stage 2 - Fitting out

For those of you who are familiar with the 250 what I found was:

  • The gyro tray now holds the 3G unit with the controller box underneath it.
  • The receiver is now pushed up to the left and held by a sticky.
  • The ESC can be attached to the side instead of underneath. By doing this the cetnner fo gravity is pretty much spot on as the electronics weigh up the heavy battery on the front.
T Rex 250 - Stage 2 - Fitting out

Stage 3 – Had an hour or two to spend it on it today so I have finished putting the head on and getting it set up on the bench. I have to say it looks real good with the silver head and with all the "clutter" gone. I think it really sets the heli off.

T-Rex 250

I went through all the instructions and set it up as the manual says. Taking it out into the garden for a first spool up it went into a perfect hover. Maybe this is fluke or maybe this is because after the 550E experience I double checked everything and got the centre of gravity spot on. Either way it hovered fine. I thought I should try Idle Up, so flicking it in the head speed almost appeared to drop. Weird.

T-Rex 250 Final with 3G

Immeidatley after seeing the head speed drop the tail let go as the belt suddenly snapped. I hit the throttle cut straight away and landed it. Bummer!

Anyway enjoy the photos! Will post a flight report when I know more!

Stage 4 – Flying Got the tail belt fixed so gave it a fight. I have to say it’s very stable in the hover, tried going upside down and but I kept getting quivers and oscilliations. I think this is a gain thing. Need to experiment, crashed it lightly a few times but all ok.

Stage - 3 - Final

Update – 21st Aug
Well, it has been some time since the last update but there have been a few things to try and not much time to do so. As I first thought this is not going to be something that takes me 5 minutes to complete. After the last attempt I reset the gains on the 3G unit and tail gain back to 35% to see what would happen. Well it was certainly excited – it almost shook itself out of the sky.

Therefore a more scientific approach was needed. Reading around and speaking to people I have now:

  • Glued the gyro/3G unit mount into the main frame to limit it’s movement under vibration.
  • Ensured the servo horn and linkage is 4.5/5mm from the centre of the horn.
  • Made the tail silky smooth by checking and redoing all the screws.  Additionally I have lubricated the tail shaft, main shaft and swash with oil to make sure it runs super smooth.
  • Set the Aileron and Elevator gains to between 9 and 10pm.

After doing this the gain is now back at 35% on the tail and it behaves *alot* better.  I think what is happening is that the vibrations and quick movements are causing it to get very confused. I tried it last night and upon repeated power ups and downs it stayed a lot more stable.  It’s not correct but I have ordered some hard dampers for the head (Align’s 3G manual recommends this)  as this should help things further.  Once these are fitted I will try some tic-tocs and see what happens.  If it can handle those then I’m almost there.

Update – 25th Aug
The super hard head dampers have turned up so I’m looking forward to fitting them so we move onto the next step. Btw I brought these TrueBlood ones from Fast-Lad Click Here

Update – 30th Aug
I finally got chance to try the new dampers, the weather this Bank Holiday weekend has been nice but very windy. The good news is the they made a big difference – it seems a lot more stable. I tried some barrel roles and it was "getting the shake on" so I reduced the Aileron gain and this helped a lot. I managed to have a go at elevator tic-tocs and flips, whilst not major stable it was a lot better and encouraging. However when I was doing a tic (or a toc I can’t remember) it fell out of the sky. I think this was pilot error but I now need to attach the linkage back to the servo arm now and a new main gear. I reckon I am getting there with this. Still needs a few more tweaks, and maybe an upgrade to V2.1 on the 3G software (currently running 2.0).

Update – 16th Sept

Ultra quick update: Had a very busy two weeks at work but I have now got the 3G data cable so I can tweak the setting on the unit! Anyway as I progress I will keep this updated! 🙂

Update – 18th Sept

This morning I hooked up my laptop to the 3G unit to see what I could do. the answer is quite simple – lots and lots.  The options are many and varied and are definitely a big step forward. I have put in the main post a document which has all the screen shots of the options available. (tagged under T-Rex 250)

The first thing I did was upgrade it from v2.0 to v2.1 apparently there are some little tweaks and stuff that help. I can’t quite find the details on the internet that tell me what the difference is between v2.0 and v2.1 but I think it should be kept up to date.

The next thing to note is that there is presets for the different types of model so it can give you a good kick in the right direction.  I therefore loaded Align’s own recommendation for the T-Rex 250 and applied that. Several of the settings changed and it seems like a good base to move forward from. I also set the gains (on the unit itself to 11 o’clock).

Test flight was next.  This proved to be good and bad.  The good bit first is that the model was a million times better, so I can highly recommend it.  The cyclic was very slow but if anything that’s a good thing and means I can make it quicker. All the wobble and stuff has gone.  However before I could do some more work, one of the links came off and it fell to the ground. 😦 Therefore I need to get some spares and get it fixed!  Still I think there is light at the end of the tunnel now!

    • stocksy
    • August 28th, 2010

    am thinking of getting my 2fiddy 3Ged soon you,re right the 2fiddy needs it, am loveing you,re blog and hope-ing you,re next blog is soon

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