T Rex 450 Pro Rebuild

[HPIguy]

Well, as some of you know, I picked up a used 450 pro 3g a couple of weeks ago. Nothing against the original owner, but I decided to tear it apart and go through the whole thing. One, I think it's a wise idea on a used bird, and two, I wanted to learn more about helis. Would have bought a kit if I hadn't gotten such a good deal.

So here you guys go, I'll add more as I progress.

---------- Post added at 11:38 PM ---------- Previous post was at 11:34 PM ----------

I got quite a ways into the build, and the instructions were off, and I had to tear the whole head back apart and start over. Oh well, I've learned a ton in the last couple weeks, more than the last two years actually. The series of tutorials and vids by finless over at HF have been priceless.

Of course, I started with centering the servos, getting the arms at 90*, and the swash level. I've noticed little touches in the Align kit that I really like, like the fact they put these two little dots on the anti roatation bracket. Simply adjust the elevator link to center the pin, then adjust your aileron and pitch servo links to level the swash, done. Nice touch IMHO

From there, you use the flybar adapter to set your phasing properly. I didn't even know what that was two weeks ago.

You want the swash level, mid stick on TX, blade grips roughly at zero, and flybar lined up dead nuts down the centerline of the bird.

Like this;

When you're done, this is what you're looking for. At mid stick on TX, you want swash level, washout arms at 90*, washout base level with the arms, rear washout ball lined up with elevator anti rotation pin, and pitch links lined up parallel to the jesus bolt and main shaft. This ensures your rotor disc and upper swash are "in phase" with each other.

Ah, perfection

Another nice Align touch. The tail blade grips have these little flanges on them.

I ddin't think anything about it until I was setting up the mechanical travel on the tail. But, if you look at them inline at mid stick, when they line up, your tail is at zero pitch, nice!

Tomorrow I'll be setting up my pitch and cyclic limits, programming the ESC, and giving it a spool up without blades to check for any vibes or issues (Thanks for that tip in your build thread Rolex!). Then hopefully off to the field on Sunday.

 

[Rolex]

One important thing about helis is understanding EXACTLY how the mechanics work and what makes it fly.
Cyclic pitch is the magic that brings it all together.
Enjoy the rebuild.

 

[neobart]

At zero trim wouldn't the heli rotate around it's axis if the tail is at zero pitch?

 

[HPI-Killer]

At zero trim wouldn't the heli rotate around it's axis if the tail is at zero pitch?

No, because HPIGuy is wearing New Balance shoes, they cancle out any negative effect while hes flying

 

[neobart]

I thought a Flux Capacitor was used for that?

 

[HPIguy]

At zero trim wouldn't the heli rotate around it's axis if the tail is at zero pitch?

Hmmmm, is this like the airplane on a treadmill question?

If it weren't for the tail rudder gyro telling it when to feed pitch in and out, it probably would. The zero pitch thing is just part of the mechanical setup to get equal servo throws in both directions, equal tail pitch slider movement both ways, etc.

No, because HPIGuy is wearing New Balance shoes, they cancle out any negative effect while hes flying

^^ I wish it worked like that, I'd sure buy many pairs if so.

 

[Rolex]

Zero pitch is for the main rotor only. The tail rotor needs enough pitch to stop the counter rotational effects.
I always set up my tail pitch without connecting the gyro, otherwise the gyro will be working constantly.

 

[HPIguy]

Zero pitch is for the main rotor only. The tail rotor needs enough pitch to stop the counter rotational effects.
I always set up my tail pitch without connecting the gyro, otherwise the gyro will be working constantly.

Zero pitch is just how mine worked out by the Align manual with the gyro unhooked. Once everything is powered up, I'm sure you are right or the heli would just spin round and round.


My maiden voyage did not go well. After a couple short spool ups to check for vibes with the blades installed, right as my skids were leaving mother earth, something caused the heli to violently tilt left and dig in. I hit the TH as quick as I could, but it was too late. Note to self, carbon blades suck for maiden voyages. Reason being, my blades are fine, but everything under them took the inertia that had to be dissipated. Damage list as of now is:

1 main shaft
1 blade grip
2 pitch links
1 set of servo gears
1 servo (bent the motor shaft) :whhooo:

Total...........about $75 retail for Align parts. Luckily I had some of it in the spares I got, and I've read good things about the RJX head which eliminates the washout block altogether so I bought an entire head for what the Align grips would have cost me. It further simplifies the already mechanically simple flybarless head (which is what drew me to FBL to begin with) as there is no need to worry about phasing anymore. Parts should be here Monday and I'll post up pics of the new head. Gotta order some Woodies too to prevent this if it goes crazy on take off again.

 

[Rolex]

You absolutely want wood blades till it's all dialed in. That's the weak point that can shatter to protect the good parts.

Try again.

 

[HPIguy]

You absolutely want wood blades till it's all dialed in. That's the weak point that can shatter to protect the good parts.

Try again.

Yep, as the old saying goes, the easy lessons never stick, but the hard ones always do. I had the carbons here, so I went ahead and used 'em. DOH!

 

[HPIguy]

Rebuild #2

The new RJX head

Center hub with direct washout arm setup, no more washout block, further simplifying the setup ease of a FBL head

RJX grips are much beefier than the Aligns

And the pitch arms bolt on, so if you rip the threads out like I did, you buy only the arm and not a whole grip

I used the Align arms again, as the RJX arms didn't give the right geometry for me. I've read fixes for it, but it was easier just to use the align arms

All done

I used the downtime for a couple other fixes

I pinned my boom

Re did my 3G mount with 3m tape

And trimmed up the case for everything. Ready to go flying this weekend!

 

[HobbyGuyMod]

Man this post couldn't come at a better time, I love the helicopter but man are they difficult to fly. I have been hitting the the sim really hard, and I bought a small TRex 100, but I have to admit I have a brand new 450 flybarless setup sitting there collecting dust. The only thing I have opened is the manual. I think I just have to man up and at least start assembling it.

 

[HPIguy]

Man this post couldn't come at a better time, I love the helicopter but man are they difficult to fly. I have been hitting the the sim really hard, and I bought a small TRex 100, but I have to admit I have a brand new 450 flybarless setup sitting there collecting dust. The only thing I have opened is the manual. I think I just have to man up and at least start assembling it.

The TR 100 is an awesome little heli, great for teaching orientation and such. If you take it slow, and follow the normal train of progression, you'll be fine with the 450. Look up Radds school of rotary flight, and the flight school section over at heli freak has great info as well. But I will say this, no matter how good the sim, it still never "feels" the same as flying an actual heli, but it does help with muscle memory for stick commands. The other big thing is there is no fear due to cost (both financial and set up time) of crashing when flying the sim, no "pucker factor" to it.

The other thing I would recommend is a Blade mCP X. Since buying one a couple months ago, my flying has progressed more than it did in the two years before that. You generally won't break anything if you fly over grass and hit TH if you get in trouble. And it's a full on collective pitch heli, so as you progress you can do some basic 3D with it. I love mine, and consider it an invaluable training tool. For as long as they make them, I'll always own one.

Good luck man!

 

[HobbyGuyMod]

Thanks for the info! And yea you are right about the pucker factor I still get it with the T100