Porpoising (?) T-Rex 450 Pro - HeliFreak
Fun, Learning, Friendship and Mutual Respect START  HERE


Unregistered
Go Back   HeliFreak > R/C Electronics Support > Skookum Robotics


Skookum Robotics Skookum Robotics SK-360 SK-540 & SK-720 Digital Flybar


Reply
 
LinkBack Thread Tools Display Modes
Old 11-06-2011, 01:13 PM   #1 (permalink)
Registered Users
 

Join Date: Jan 2009
Location: London
Default Porpoising (?) T-Rex 450 Pro

This heli: hovers well; when hovering, responds hapilly to sharp elevator input; slow forward flight is good; fast forward flight is a bit more strange.

FFF is sometimes pretty (very ?) good; but if there's wind, it's a bit like a jeep bouncing over a rough road [*]. It's perfectly controllable, but not very tidy.

I think what I'm seeing is oscillation in the pitch axis. Opinion at the flying club is that it's porpoising/dolphining. Something common with FBL systems ?

Increasing cyclic damping prompted more severe oscillations... [Lucky I had another bank to switch to... ]

So, what causes porpoising ?

Is there a rule of thumb covering what to do ? Reduce overall cyclic gain ? Reduce specific elevator gains ? [Elevator Hiller ?]
[*] Well, that's what comes to mind. I dn't actually know much about jeeps...
Scallybert is offline        Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 11-06-2011, 02:11 PM   #2 (permalink)
 
Posts: 11,311
 

Join Date: Mar 2007
Location: United Kingdom star
Default

=] hi, are the Houses of Parliament intact? lots of fireworks going off there!

the gyro is overshooting, like a tail gyro wag but in the vertical axis, essentially the same thing. can you post a log with software settings.
__________________

georgi UK is offline        Reply With Quote Quick reply to this message
Old 11-06-2011, 02:52 PM   #3 (permalink)
Registered Users
Thread Starter Thread Starter
 

Join Date: Jan 2009
Location: London
Default

Quote:
Originally Posted by gmcallister View Post
=] hi, are the Houses of Parliament intact? lots of fireworks going off there!
I think so. However, we're in Hackney, (Hackerney...) and they are slightly out of sight - though I might be able to see Canary Wharf...

Quote:
the gyro is overshooting, like a tail gyro wag but in the vertical axis, essentially the same thing. can you post a log with software settings.
Ah, a log... Is there a guide to creating/using logs ? [I'm guessing I'd have had to turn something on before I went flying.]

Settings (from memory) are 'sports', with: Hiller Decay halved; Rate ~7/8 of default; Cyclic Gain is locked to 70% (in one bank, that exhibits the problem).

So, analogously to tail wag, just backing off the cyclic gain should help ? More specifically, the elevator gains ?
Scallybert is offline        Reply With Quote Quick reply to this message
Old 11-06-2011, 03:10 PM   #4 (permalink)
 
Posts: 11,311
 

Join Date: Mar 2007
Location: United Kingdom star
Default

=] the Bow Bells in earshot?!

I was originally looking for the servo arms being too long (as in a tail wag) but to have such a high cyclic gain will create the same prob. no question.

40% or below will suffice, all that happens is the gyro becomes more restricted, there is no gain or pun in doing this!

FAQ says how to upload files here.
__________________

georgi UK is offline        Reply With Quote Quick reply to this message
Old 11-06-2011, 05:13 PM   #5 (permalink)
Registered Users
 
Posts: 4,552
 

Join Date: Jul 2007
Location: Melbourne Oz
Default

I am seeing a similar thing with my mini Protos (350mm blades), and have just been flying around it. With the gain at 60%-70% it is worse but I am not seeing any bounce on sharp inputs, dropped the gain to 55% and it is a little better but still there. Your description is spot on, it looks untidy and bobbles in fast forward flight and in wind. I was raising the gain as it didn't feel as locked in with the gain at 50% where I started.

//Dennis.
__________________
SOXOS DB7 : SOXOS 600 : SOXOS 550 : SOXOS F3C
Protos 380 : SAB Goblin 700 nightflyer : Jeti DS-16 : Mini Protos FBL Stretch : Logo 600
www.soxosaustralia.com.au & VTX blades
Thunder Fighter is offline        Reply With Quote Quick reply to this message
Old 11-06-2011, 06:27 PM   #6 (permalink)
Registered Users
 

Join Date: Oct 2009
Location: UK/Switzerland
Default

Try increasing/decreasing elevator damping gain and see what happens.
__________________
Blade mCP X - Brushless, XP-7A, HP05S
Gaui X2, BeastX/Scorpion 3400kv/YGE-30A/GS-093/DS95i
Align AH-1 Cobra (T-Rex 500)
Align T-Rex 600 EFL Pro, SK720/600MX/YGE-90HV/BL9180/BL9188
zeeflyboy is offline        Reply With Quote Quick reply to this message
Old 11-06-2011, 06:46 PM   #7 (permalink)
Registered Users
Thread Starter Thread Starter
 

Join Date: Jan 2009
Location: London
Default

Quote:
Originally Posted by gmcallister View Post
=] the Bow Bells in earshot?!.
I think the wind would have to be very strong & in the right direction...

Quote:
I was originally looking for the servo arms being too long (as in a tail wag) but to have such a high cyclic gain will create the same prob. no question.

40% or below will suffice, all that happens is the gyro becomes more restricted, there is no gain or pun in doing this!.
The RJX head has quite long arms on the grips, so actually has a similar swash travel to an FB head - so the same servo arms as FB seem suitable.

I've basically approached setting the cyclic gain the same way I would with a tale gyro. ie up the gain until you get oscillation, then back off a bit. The oscillation I was provoking through cyclic input was at >70% gain - so I figured I was ok. I was thinking that the bobbing around I was seeing was due to too little gain, rather than too much - probably...

Quote:
Originally Posted by Thunder Fighter View Post
I am seeing a similar thing with my mini Protos (350mm blades), and have just been flying around it. With the gain at 60%-70% it is worse but I am not seeing any bounce on sharp inputs, dropped the gain to 55% and it is a little better but still there. Your description is spot on, it looks untidy and bobbles in fast forward flight and in wind. I was raising the gain as it didn't feel as locked in with the gain at 50% where I started.
Yes. I've got a set-up that seems to hover very tidily. I think I'll copy that bank to the other one, then significantly drop & try various gains (from the Tx) on that bank.

Since the problem seems to be with the pitch gains, rather than roll gains; when I've got the pitch gains set in that bank, I might try and tweak the effective roll gains back to the higher values in the other bank. Or not.

What was interesting was that trying to use damping gain to damp out the bobbles provoked oscillation. No different to overdoing the gain on a rate tail gyro, I guess.
Scallybert is offline        Reply With Quote Quick reply to this message
Old 11-06-2011, 06:49 PM   #8 (permalink)
Registered Users
Thread Starter Thread Starter
 

Join Date: Jan 2009
Location: London
Default

Quote:
Originally Posted by zeeflyboy View Post
Try increasing/decreasing elevator damping gain and see what happens.
Increasing that (rather too much) was today's experiment - it got moderately exciting..
Scallybert is offline        Reply With Quote Quick reply to this message
Old 11-15-2011, 02:28 PM   #9 (permalink)
Registered Users
Thread Starter Thread Starter
 

Join Date: Jan 2009
Location: London
Default

So anyway, down at the field last weekend, and I thought that I'd fixed the problem by reducing the cyclic gain.

However, it seems taht I couldn't reproduce the problem with the previous gain (& settings), so I haven't actualy 'fixed' it.

My guess is that the problems were maybe related to the wind conditions, and these weren't present this time out.

Anyway, I'm now running with the gain at 45%. It does seem that maybe the hovering was more precise with the previous 70%.
Scallybert is offline        Reply With Quote Quick reply to this message
Old 11-16-2011, 09:17 PM   #10 (permalink)
Registered Users
 
Posts: 4,552
 

Join Date: Jul 2007
Location: Melbourne Oz
Default

I think it is related to wind, when I have flown indoors the heli didn't display the same issues. I haven't been able to test anything as I have been traveling.

//Dennis.
__________________
SOXOS DB7 : SOXOS 600 : SOXOS 550 : SOXOS F3C
Protos 380 : SAB Goblin 700 nightflyer : Jeti DS-16 : Mini Protos FBL Stretch : Logo 600
www.soxosaustralia.com.au & VTX blades
Thunder Fighter is offline        Reply With Quote Quick reply to this message
Old 11-17-2011, 06:05 PM   #11 (permalink)
Registered Users
 
Posts: 12,250
 

Join Date: Jul 2010
Location: spokane,washington
Default

Man, 70% gain? At 60 mine is bobbing almost out of control violently.

Another thing to contemplate. Is the heli balanced with the battery you are flying? If not the heli will tend to bob at different throttle rates since the Sk is trying to also overcome the weight dispensation issue. Indoor flying tends to have the heli fly at one rate of head speed whereas outside this is not as consistent. Just a thought.
__________________
Roughly 400 helis built over the years. Nuff said.
Luvmyhelis is offline        Reply With Quote Quick reply to this message
Old 11-17-2011, 07:33 PM   #12 (permalink)
Registered Users
 
Posts: 4,552
 

Join Date: Jul 2007
Location: Melbourne Oz
Default

Mine is balanced on the mainshaft and I did try different head speeds indoors. It could be a geometry issue as I was also able to get the main gain up to 70% without wobbles on stops and at 50% it doesn't feel really locked in. I am at 55% now and in wind it still bobbles/porpoises.

//Dennis
__________________
SOXOS DB7 : SOXOS 600 : SOXOS 550 : SOXOS F3C
Protos 380 : SAB Goblin 700 nightflyer : Jeti DS-16 : Mini Protos FBL Stretch : Logo 600
www.soxosaustralia.com.au & VTX blades
Thunder Fighter is offline        Reply With Quote Quick reply to this message
Old 11-27-2011, 05:33 AM   #13 (permalink)
Registered Users
Thread Starter Thread Starter
 

Join Date: Jan 2009
Location: London
Default

Quote:
Originally Posted by Luvmyhelis View Post
Man, 70% gain? At 60 mine is bobbing almost out of control violently.
IIRC, I;ve got the 'hovering' FM at cyclic 60% now, and the FFF FM at 45%. It was windy yesterday, and the cyclics seemed to be behaving themselves.

I managed to get the tail out of shape, though...

I guess headspeed and other mechanical/servo factors will have a big effect on how high a gain you can run.

I'd expect headspeed to effectively increase the gain (so you may have to reduce the gain), whereas any delay in the servos/etc is going to hurt things.

Quote:
Another thing to contemplate. Is the heli balanced with the battery you are flying? If not the heli will tend to bob at different throttle rates since the Sk is trying to also overcome the weight dispensation issue. Indoor flying tends to have the heli fly at one rate of head speed whereas outside this is not as consistent. Just a thought.
Yes, I did check the balance - but it can't do any harm to look again. I guess there may also be some variation between packs - which may not all be identical.
Scallybert is offline        Reply With Quote Quick reply to this message
Reply




Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the HeliFreak forums, you must first register.
Please enter your desired user name, your REAL and WORKING email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself. Use a real email address or you will not be granted access to the site. Thank you.
Email Address:
Location
Where do you live? ie: Country, State, City or General Geographic Location please.
Name and Lastname
Enter name and last name here. (This information is not shown to the general public. Optional)
Helicopter #1
Enter Helicopter #1 type and equipment.
Helicopter #2
Enter Helicopter #2 type and equipment.
Helicopter #3
Enter Helicopter #3 type and equipment.
Helicopter #4
Enter Helicopter #4 type and equipment.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Display Modes

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On




Copyright © Website Acquisitions Inc. All rights reserved.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
 

SEO by vBSEO 3.6.1