Questions, how existential. TRex450

[jrohland]

I got my SK360 in Saturday's post (today is Monday). Sunday morning I installed it on my TRex 450. After setting the channel and servo reverse settings and servo subtrims (to center the servo horns), I took it out front and flew it. A bit touchy but, I put the expo back on to the aileron and elevator after which, it actually felt about the same as with the flybar.

I took it to a large field and test flew. Standard sport flying (figure 8s), all was normal.

Tried a piro, now things get fun. After about 4 or 5 piros, it suddenly rolled to port. Did I screw up? Try again. Same thing, after 4th or 5th piro, rolls violently to port. I'll look into that.

Try flips and loops. Stick timing is different but, filps and loops are fine, if slow. Ok, I need more degrees of pitch. Currently it is between 6 and 7 degrees.

Try a roll. Wow, it got so screwed up in the roll, I could not even figure out what went wrong. Try another roll (to port as before), this one is even more crazy. One issue is the roll starts 2 beats after I move the stick. That delay is messing with my collective timing in a nasty way. Second issue, the roll speed is waaaay slooow. I have about 8 degrees of aileron but, that is not nearly enough.

Out of the box, this unit is highly recommended for scale birds. With minimal setup it should fly a flybarless scale in scale flying style very well.

It is clearly going to take me a while to get everything dialed in for 3D style flight.

I have a Kontronik Jazz 40-6-18 ESC. I am using the ESC's BEC which is rated for 5 volts. The heli runs on 4s LiPo power with a NEU 1107-2Y (3400 kv) motor. Headspeed it right about 3000 RPM. Gyro is a GY401 at about 35% gain.

Question? What servos are recommended for this heli. I left on the HiTec HS65MG servos I have been using for years. These may be too weak and inaccurate for the flybarless setup.

I know I want digitals. Should I worry more about torque than speed? What servos have shown good results in this application?

By the way, I also installed an FMA Direct Copilot on this heli. It was not used (althoug it is wired in) during any of the above testing.

jrohland

[Skookum]

>Ok, I need more degrees of pitch. Currently it is between 6 and 7 degrees.

Do you mean collective or cyclic pitch? If your cyclic pitch is only 6-7 degrees then it may "let go" suddenly in FFF or on hard collective, when it runs out of cyclic pitch to apply.

>Tried a piro, now things get fun. After about 4 or 5 piros, it suddenly rolled to port. Did I screw up?

Piros are the hardest thing for a flybarless system to handle. Everything has to be right:

1) The balance needs to be right under the mainshaft
2) the swash needs to be level in setup mode at max, min, and zero collective pitch
3) You may want to adjust the tail-drag compensation to better match your helicopter
4) You need strong, fast servos pref digital and with no slop in linkages

>Try a roll. Wow, it got so screwed up in the roll, I could not even figure out what went wrong. Try another roll (to port as before), this one is even more crazy.

Possibly the phasing is off. Check the phasing using the procedure in section 6 of the manual.

>>One issue is the roll starts 2 beats after I move the stick

That sounds like the bell gain isn't high enough. "Bell" action gives direct motion of the swash, and a snappier response. If it's too low you get sluggish initial response, if too high you get a kick-back at the end of a maneuver. Stiffer than normal head damping also helps.

>Second issue, the roll speed is waaaay slooow. I have about 8 degrees of aileron but, that is not nearly enough.

Don't try to adjust aileron or elevator rates using cyclic pitch range. The place to adjust rates is on the advanced tab. You want the cyclic pitch range to be the same for aileron, elevator. Also, try to keep the swash mixing %'s below 60% to prevent interaction at max collective.

If you'd like I can look at your setup file, just send it to the email at the back of the manual

[jrohland]

Skookum, please note, all of these tests where done with default settings. I found the SK360 very impressive. That the heli flew so well with the default settings is a testament to your good desgn.

Now the detailed tuning starts.

Again, the question is, what collective servos should I get for the TRex 450?

jrohland

[banshee_biker]

Originally Posted by jrohland

Again, the question is, what collective servos should I get for the TRex 450?

jrohland

I think both the JR DS285 MG and the new Hitec 5065Mg (Not out yet) are the most common digital servos that fit in a trex 450, I myself have ds285 mg's and they have survived many hard crashes. I am still running a flybar but hope to switch very soon. Also you may want to get a better swash like a beam E4 (direct replacement) or similar, the less slop in the head system the better off you will be. I think that is just as crucial as digital servos. check your links too and replace if sloppy.

other's here have more experience than me and Im sure they will reply soon too!!

[Skookum]

>Again, the question is, what collective servos should I get for the TRex 450?

Digitals are ideal, but Alvin's 3D demo videos with the Trex 450 are all with HS65's analogs, and a fairly stiff rotor head with little slop.

If I remember right Alvin did note that after a few consecutive piros it would "fall out" of the maneuver. Piros were better in a (larger) Logo 500 with super fast digitals, or a larger rotor diameter on the Trex via longer blades or a wider head.

[SpeedVision]

I opted for the HYPERION ATLAS DS 11 AMB servos. They are MG servos and have tons of torque... Speed is .15 sec at 6 volts, I believe... Best part is the programmable feature for servo centering and they are a steal at less than 35 bucks each. They also have a super fast servo at .05 on 6 volts at the expense of torque.

Overall feedback on Hyperion servos has been positive, especially at their price point.

[Skookum]

>HYPERION ATLAS DS 11 AMB

Thanks I hadn't heard of those before, I'll have to try them.

[WhirlingBladesOfDeath]

Originally Posted by Skookum

Also, try to keep the swash mixing %'s below 60% to prevent interaction at max collective.

My Elevator, Aileron, Collective are set to 65, -65, 50 respectively on my swash tab. Is that "close enough" to below 60, or should I really try increasing the travel % on the servos a smidget on the servo tab, and then readjust everything accordingly? Currently the server travel % is set to 100%.

Thanks,
Jason

[int2str]

Can you post a picture of your head setup?

[WhirlingBladesOfDeath]

Here is a crappy cell phone pic. What exactly are you looking for?


Thanks,
Jason

[WhirlingBladesOfDeath]

Actually, now that I'm thinking about it, I did 2 things to reduce the throws on the stock setup. First, I added the Trex-500 control longer arms to the main blade grips. I also moved the ball link in on the servo arms. (I'll try to find a pic) Maybe I should move the control balls back to the stock position on the control arms?

In other words, did I maybe get enough throw reduction just with my main blade grip mod?

Thanks,
Jason

[WhirlingBladesOfDeath]

Here is a better picture, but taken before I had my CF piece to keep the swash in phase. But mechanically, the head and swash ratios still work the same. You can also see the original holes in the servo arms, and how much I moved them in.


Thanks,
Jason

[int2str]

Jason, that's a sweet setup!

But I was looking for a picture from jrohland, since I have a T-Rex 450

[WhirlingBladesOfDeath]

[jrohland]

Originally Posted by int2str

Can you post a picture of your head setup?

Check this tread. I have posted two photos there.

jrohland

[Skookum]

>My Elevator, Aileron, Collective are set to 65, -65, 50 respectively on my swash tab. Is that "close enough" to below 60... Currently the server travel % is set to 100%.

It'd be better to have them below 60, or the gyro could run out of cyclic pitch while at max collective due to interaction. Probably the blades would already be stalling by then anyways...but its still a good idea. This isn't a big deal, but it can be surprising if it "blows out", ie pitches up (or down...) suddenly because it ran out of cyclic pitch to apply.

You shouldn't have to re-measure, you could just go 110% on all the servo throws and then
59,-59, 46 on the swash mixing would be exactly the same.

[int2str]

jrohland,

Looks like you're running direct swash -> blade grips linkages on your 450. This will lower the resolution the gyro has available to make corrections. Does this seem to work ok for you?

I really like this setup but was aftraid it wouldn't work. rc-expert (or so) makes a flybarless head for the 450 which has blade grips that could be extended outwards to give it a bit of a mixing range. I may try that if nobody else comes through soon.

[andersnorlin]

Originally Posted by int2str

rc-expert (or so) makes a flybarless head for the 450 which has blade grips that could be extended outwards to give it a bit of a mixing range.

Do you have a link to that flybarless head I could not find it?

thank's,
Anders

[jrohland]

Originally Posted by int2str

jrohland,

Looks like you're running direct swash -> blade grips linkages on your 450. This will lower the resolution the gyro has available to make corrections. Does this seem to work ok for you?

I really like this setup but was aftraid it wouldn't work. rc-expert (or so) makes a flybarless head for the 450 which has blade grips that could be extended outwards to give it a bit of a mixing range. I may try that if nobody else comes through soon.

Thanks to bad weather, I have not flown this setup (other than a short hover in my front yard). I should have a chance to test fly this afternoon.

If you noticed, I placed the ball links as close to the inside of the servo horns as I could. This increases the distance the servo must rotate to move the link. I'm hoping that will give me enough torque and resolution. If it does not, I may go to longer ball offsets on the swashplate servo links. This is not ideal because I would be chaging the geometry without fully understanding the ramifications--as though I have not done that already.

We really need somebody to engineer a flybarless head for 400 sized helis. I hope some company steps up to the plate soon.

jrohland