T-Rex 250 Build Thread

[Blade201]

Originally Posted by hga77

Did you trying switching servos on the rx connectors to see if another servo would work on the Aileron channel? What battery were you using? Maybe it was running low.

Thanks, but neither did the job. Purchasing another one from my LHS. Thanks again.

[tommeke]

got it all dialed in now wowie, nice little heli. have maidened it succesfuly and tomorrow I'll throw some flips at it, we'll see how it goes

[RickVS]

Hi. I'm building my first heli, the trex 250 SE. I have it all together, now I need to plug everything in. There are 4 servos. I figured out that the tail servo plugs into the receiver's 'rudder' connection, however where do the other three plug into? Which are aux1, ail and elevator? Also, I see where the gyro and the receiver go in the heli, however there doesn't seem to be room for the ESC. Where did you put this on your heli? Finally, what is the difference between the 250 pro and the 250 SE? Thanks! Rick

[hga77]

Originally Posted by RickVS

Hi. I'm building my first heli, the trex 250 SE. I have it all together, now I need to plug everything in. There are 4 servos. I figured out that the tail servo plugs into the receiver's 'rudder' connection, however where do the other three plug into? Which are aux1, ail and elevator? Also, I see where the gyro and the receiver go in the heli, however there doesn't seem to be room for the ESC. Where did you put this on your heli? Finally, what is the difference between the 250 pro and the 250 SE? Thanks! Rick

The tail servo plugs into the Gyro. The Gyro plugs into the rudder channel. Depending on the Gyro you have, a second wire (normally a single wire) also plugs into the rx (reciever) into the gear channel (or other channel depending on your rx), so that you can control the gain value from the transmitter (tx).

The three remaining servos that control the swashplate (known as the "cyclic" servos since they move the cyclic ie. elevator+aileron), go into the corresponding channels for each and depends on the rx you have (refer to rx manual). Most rx's have the channels labelled on the casing to describe what each input channel is. Spektrum rx's typically have the labels as abreviated words.

Spektrum example:
- AUX1 - (pitch servo)
- GEAR (typically kept for gyro gain)
- RUDD (Gyro)
- ELEV (elevator servo)
- AILE (aileron servo)
- THRO - (esc connects here for motor throttle)
- BATT - (you would use this if you are using an external bec otherwise no need for this since power come with esc. But you can use this while setting up heli head/servos on the bench etc using an external batt).

On Futaba recievers, channels are represented as numbers. Again refer to rx manual.

While building my 250 a while back I compile a doc. Attached

[hga77]

Originally Posted by RickVS

Where did you put esc on your heli?

Here's what I did:
https://www.helifreak.com/showpost.p...postcount=1231

Have a look at what others did too in that thread

Originally Posted by RickVS

What is the difference between the 250 pro and the 250 SE? Thanks! Rick

I believe it's just the placement of the tail servo. Maybe new main grips too not sure.

[msedhom]

I just bought a semi built Trex 250 off here and looking forward to the build. It has the upgraded SE tail and align FBL head. Will be putting my spare 3GX on it.

Whats the difference between the original 250 and the SE/Pro? Also, I'm about to buy a custom canopy off fusuno, I'm guessing only the Trex 250 canopies fit, otherwise they wouldn't be selling an SE or Pro canopy.

[hga77]

As far as i remember:
- silver head assembly (original was black)
- tail grips
- canopy
- mounting servos. With original i dont think you had the rubber plastic gromets to secure the servos in place.

Just download both old and new manuals and check that way.

[msedhom]

Awesome thanks for that. Stock DS420 tail servo ok?

Sent from my GT-I9000 using Tapatalk 2

[hga77]

Originally Posted by msedhom

Awesome thanks for that. Stock DS420 tail servo ok?

Sent from my GT-I9000 using Tapatalk 2

Works for me with no wagging. But make sure you mechanical setup is as best as you can have it and that the tail pitch slider is smoooooooth. If not silcky smooth then you need to track the binding throughout the tails assembly and eliminate ut. If you make it smooth and have perfect machanical setup, you'll be fine. Watch finless trex250 build videos he covers this in there.

[hga77]

I'd also recommend the hiem set for the tail grips. It removes the slop in the grips.

[msedhom]

Great advice, thanks heaps!

Sent from my GT-I9000 using Tapatalk 2

[rk295]

Hi guys,

I'd like a bit of advice please. I rebuilt a part of the head on my HK250 last night with real Align parts, the bits I replaced were the main rotor housing and the fly bar control assembly. I also replaced the worn original HK ball links with Align ones. But I'm finding the ball links are _really_ tight on the balls. One of the pitch adjustment ones hardly moves causing the fly bar to move up when I push positive pitch - because the link is so tight the blade grip isnt moving.

I've checked the blade grip is free to spin around on the feathering shaft and it is fine, the problem is the ball link.

Are the HK balls likely to be slightly larger than the Align ones? I tempted to ream out the ball links, but there is so little material around the connector I'm worried about weakening it.

r.

[hga77]

Originally Posted by rk295

Hi guys,

I'd like a bit of advice please. I rebuilt a part of the head on my HK250 last night with real Align parts, the bits I replaced were the main rotor housing and the fly bar control assembly. I also replaced the worn original HK ball links with Align ones. But I'm finding the ball links are _really_ tight on the balls. One of the pitch adjustment ones hardly moves causing the fly bar to move up when I push positive pitch - because the link is so tight the blade grip isnt moving.

I've checked the blade grip is free to spin around on the feathering shaft and it is fine, the problem is the ball link.

Are the HK balls likely to be slightly larger than the Align ones? I tempted to ream out the ball links, but there is so little material around the connector I'm worried about weakening it.

r.

Maybe get align balls or HK links. Basically matching the balls and links. But i'd defenitly have a go at reaming the links first, In very small amounts.

[Jasmine2501]

Originally Posted by rk295

Are the HK balls likely to be slightly larger than the Align ones? I tempted to ream out the ball links, but there is so little material around the connector I'm worried about weakening it.

r.

Get a spare ball and a spare canopy mounting pin - screw the ball into the mounting pin and put lock-tite on it, you never want it to come loose. Next, take a knife and score the ball lengthwise - this will create a microscopic cutting surface on the ball. Stick the ball in a link and rotate it all around until it loosens up a bit. Good to go! Tight links are a known issue on the 250 - size them as best you can, then do a few flights and it should be fine. Try to balance them - if there's a tight link on one side, put a tight one on the other side too, and they will wear more evenly.

[joeblades]

Originally Posted by Jasmine2501

Get a spare ball and a spare canopy mounting pin - screw the ball into the mounting pin and put lock-tite on it, you never want it to come loose. Next, take a knife and score the ball lengthwise - this will create a microscopic cutting surface on the ball. Stick the ball in a link and rotate it all around until it loosens up a bit. Good to go! Tight links are a known issue on the 250 - size them as best you can, then do a few flights and it should be fine. Try to balance them - if there's a tight link on one side, put a tight one on the other side too, and they will wear more evenly.

Nice idea Jasmine...that got me to thinking. Dremel has some very small ball cutters, I have not checked but they may have some small enough to work. Of course you would not want to put them in a dremel tool and use them, but by hand they may work very well.

[rk295]

Originally Posted by Jasmine2501

Get a spare ball and a spare canopy mounting pin - screw the ball into the mounting pin and put lock-tite on it, you never want it to come loose. Next, take a knife and score the ball lengthwise - this will create a microscopic cutting surface on the ball. Stick the ball in a link and rotate it all around until it loosens up a bit. Good to go! Tight links are a known issue on the 250 - size them as best you can, then do a few flights and it should be fine. Try to balance them - if there's a tight link on one side, put a tight one on the other side too, and they will wear more evenly.

Nice to know I'm not the first to have the problem. I love the idea btw, nice one! I'll have a little play tonight. I've flown it and things seem ok, but I dont like how tight they are. Next month when I get paid I think I'll order up some Align balls and some fresh ball links and have another go at it. Cheers for the tip mate, very useful!

[Jasmine2501]

Well, you can get an actual 250-size ball link sizer, but when the 250 was new, nobody had it yet, so that's when I came up with the idea of using a spare ball - the canopy pin just happened to be something with the right threads to hold it with. A feathering shaft might work too. This is a cheap way to make a ball link sizer for any size - the 450 balls fit on the canopy pin from the 450 also.

[Thermikflieger007]

T-Rex 250 Pro DFC Microbeast Bau und Testflug (Build and Flight) (5 min 54 sec)

[seattleite09]

Hi everyone. I read a thread the other night where people were complaining about this issue, where the torque tube front gears get detached from each other mid-flight, causing the heli to start spinning out of control.

This happened twice to me before I finally did some research and found that thread. Most recently this week, everything went great for the first flight (normal mode); then for the 2nd flight I started in IU1 with a flat throttle curve at 70%. I was simply hovering nose in, 2m off the ground, when I heard a change in the motor sound/pitch, and the heli started spinning to the left and crashed. Luckily I managed to hit TH on the way down, minimizing the damage.

What broke: the feathering shaft was ripped apart, causing the rotor head to detach. The black umbrella gear obviously detached from the other black gear, and I suspect that's what caused the crash in the first place.

Does anyone have an update on how to fix this for good? I've put new parts in the heli, looks good and all, but I won't fly it until I understand how to fix this problem once and for all. I mean, gears failing in mid-flight while hovering is simply unacceptable. And highly unsafe.

Thanks in advance for your feedback/suggestions.