450x began to spin wildly after changing I/U back to normal flight mode! Help!

[stevec1906]

I bought a second hand 450x recently on eBay (I'm aware this was risky but I felt like taking a chance!) and it is stock apart from Savox 0257 servos on the cyclic and Align 3G blades. The original tail servo remains. It's setup as per the instructions from the manual except for 50% D/R to tame it down a little. All has been well and as a newbie I've only been hovering this heli tail in out in the garden on very calm days. I have an MCPX v2 I mess about with the rest of the time. I've only been into this hobby for a few months. Anyway, I was hovering in the garden for around 3 mins when curiosity finally got the better of me and I flicked my DX6i into I/U. It shot up about ten feet due to the higher headspeed and while I managed to maintain control over it the throttle was very sensitive and it was quite difficult to keep a constant height once I got it back down. I then changed from I/U back to normal flight mode about ten feet off the ground to try and regain some composure and the tail began to spin hard to the left after half a second, without any input from me, and in true newbie style I binned it by reducing the collective to zero in a blind panic. I've read about different setup issues that cause this heli to spin but can't find anything to do with changing flight modes. I've replaced all the broken and bent parts and after spooling it up on level ground it seems to be reacting predictably again. I'm obviously worried it may happen again and wondered if someone with experience can help me identify what caused the issue in the first place. Could it be the AR7200bx is faulty? Should I reset it and set it up again from scratch? Possible ESC issue? Any and all opinions will be greatly appreciated.

[450man]

I am just starting to use IU and one of the things worth checking is that the pitch curves are the same between normal and IU. If they aren't then you will get that sudden climb or drop but if the pitch curve in all modes is the same from mid-stick up then it shouldn't jump when switching to IU. If it jumped up when going to IU then it would jump down when going back to norm.

Can't help with the spinning though...

[stevec1906]

It's the spinning that's the major problem to be honest. I thought that if the pitch was the same but you increased head speed that you would still get lift anyway, no? As I changed the mode back I was expecting it to drop so countered it with a little extra throttle so it wouldn't drop dramatically but then it started to spin wildly. I checked the battery voltage after just to be sure but it was fine. Like I said, I'd read about a few tail spinning issues but can't find any that have the same circumstances as me.

[Leigh Beaumont]

Is the 50% D/R on the tail or cyclic?

[Leigh Beaumont]

Also check there are trims altered in idle up this is easy to miss, and make sure expo and D/R are same from normal to idle up as these can be different also. If i was you as its second hand I'd do a complete set up mechanical to beastX. That's where I'd start first

[iceuk]

Tail won't spin uncontrollably just because your are in iu you just had dt moment.

[Leigh Beaumont]

Could be DT but I'd check setup up first and make sure setup is correct. Also if he is running 50% DR on tail thats a bad idea

[450man]

That's right... it is possible to set up the DX6i so that the trim can have a different position set in each mode. I had forgottent that.

Definitely worth checking but didn't the OP say he lifted off in normal and switch to IU and he didn't have a problem when he lifted off... only when he switched back to norm from IU? That would suggest that trims in norm were at least acceptable.

Other things that I would check are: sticking tail rotor slider, an issue with the tail servo, problem with AR7200BX but I would double and treble check set up before moving on to other things.

[Guest]

If the headspeed in IU is massively different (which from how you explain what happened this sounds to be the case) to normal flight mode, the sudden change can cause all sorts of odd things to happen, the amperage pulled by the motor could half, leading to surges and spikes in the FBL unit and servos. Would be a good idea to ask someone who is confident in control to test fly it after you adjust your pitch and throttle curves. As a rough starting point I would set your UI throttle the same as the 75% figure in your normal mode and copy the pitch curve from your normal mode, you won't need a linear 0,25,50,75,100, as you won't be doing any 3D stuff...!!

I'm not an expert, but I speak from experience....I would suggest as previous members have suggested that you do a complete re-set-up of the heli, the BeastX is fairly simple, I found the Microbeast version of the manual slightly easier to follow until you get used to doing it, the explanations and text are more detailed than the Spektrum version. The first time I did a set-up it took me over 4 hours, there is no rush and the more accurately you do it, the better your heli will fly!!

[tomatwalden]

As the heli is second hand, I would check the tightness of the belt to the tail rotor. It's not uncommon on the Blade 450's for the boom to slip a little, and you lose tension in the belt which could also explain the loss of tail authority.

As others have said, check the pitch curves between IU and normal. At about 50% stick, they should both give the same pitch. The increased headspeed will make a *VERY* minor difference, but a severe jump in altitude means a different pitch curve.

[450man]

If the headspeed in IU is massively different (which from how you explain what happened this sounds to be the case) to normal flight mode, the sudden change can cause all sorts of odd things to happen, the amperage pulled by the motor could half, leading to surges and spikes in the FBL unit and servos. Would be a good idea to ask someone who is confident in control to test fly it after you adjust your pitch and throttle curves. As a rough starting point I would set your UI throttle the same as the 75% figure in your normal mode and copy the pitch curve from your normal mode, you won't need a linear 0,25,50,75,100, as you won't be doing any 3D stuff...!!

I'm not an expert, but I speak from experience....I would suggest as previous members have suggested that you do a complete re-set-up of the heli, the BeastX is fairly simple, I found the Microbeast version of the manual slightly easier to follow until you get used to doing it, the explanations and text are more detailed than the Spektrum version. The first time I did a set-up it took me over 4 hours, there is no rush and the more accurately you do it, the better your heli will fly!!

This is a really good post IMO. I agree.

[Mike00top]

Hi SteveC my guess is something like this

Norm mode throttle follows stick, IU 100% throttle across the board, so my theory is (unless you find a mechanical fault) is this is what just happened

while in IU the heli is revving much higher but with a lower pitch angle and as you were not climbing or descending fast there was little torque on the heli, now then when the IU was dropped back to NORM a few things happened all at once, firstly the revs dropped and secondly the heli started to descend short after, which for sure you would have countered by adding throttle/collective at which point the heli spun round, this is due to a massive torque reaction from the motor accelerating hard and adding pitch, this is a classic case for flyers flying in NORM mode, and then finding the tail steps out

by all means check the ship over mechanically, thats always wise, but if there is nothing wrong, the above explanation is why

most powerful heli's need to be run in IU, they fly far nicer mostly due to more constant head RPM's and less dramatic torque changes.

[stevec1906]

450x began to spin wildly after changing I/U back to normal flight mode! Help!

The D/R is set to 50% for everything and I've been through the trims and everything else I can think of to see if there are any differences between I/U and normal mode and there aren't. Two more questions:-

-What is DT?
-Why is 50% D/R bad for the tail?

[Mike00top]

The D/R is set to 50% for everything and I've been through the trims and everything else I can think of to see if there are any differences between I/U and normal mode and there aren't. Two more questions:-

-What is DT?
-Why is 50% D/R bad for the tail?

50% set on tail, may well reduce the throw of the pitch available to the tail, ( possibly not enough )

DT is a dumb thumb moment or brain fart

[stevec1906]

450x began to spin wildly after changing I/U back to normal flight mode! Help!

Thanks for your input everyone. I feel as though I have a much better understanding of what has caused the reaction in my heli through changing modes. I'm going to perform a complete re-set up of the heli and go from there. Just for future reference, can I take it that it's a better idea to change to and from I/U while the heli is still on the ground?