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View Full Version : MX400 Pro vertical axis rocking/bobbing/wobble. HELP!!!


essence25
09-30-2006, 03:53 AM
Hello all,

I'm going crazy trying to figure out whats causing my MX400 pro to rock/bob on the vertical axis, while hovering. Seems to go away while the heli is in motion. Blades are balanced, swash plate is ok, no play in the vertical shaft, feathering shaft is new, blade grips are new etc. I have aluminum headblock and aluminum slider, aluminum main shaft collars. New main gear set.

It doesn't seem to be a tail problem since it is only going up & down not sideways. I also checked the CG and seems to be ok. Using 2100 Mah 16C LIPO (http://www.rcuniverse.com/buynow/keywordclick.cfm?bid_id=3446) Hyperion (http://www.rcuniverse.com/buynow/keywordclick.cfm?bid_id=3406).

I have 0 vibration on the body of the heli since I have a mini antenna and that antenna is very sensitive to movement, it is rock still.

I bring the heli into hover and in a few seconds it starts to do that vertical rocking. Seems to be more pronunced as the battery is toward the end of the charge.

I'm expecting it to hover rock still, is this normal or its me wanting too much. I got the bird nicely trimmed and with no vibration etc.

I hope some experts know whats going on as it is driving me crazy.

I thank you for any advice..


ESC 25A HeliMax (stock) Motor HELIMAX 2580KV (stock) Gyro Align RCE-500X. Servo's 2 X hitec HS65HB (mighty feather) 1 Futaba S3107 (aileron)
1 x HDS-877 Digital (tail).

Custom Heat sink on ESC and heatsink collar on motor. No overheating problems.

Blades: 325MM Align in T-rex XL stock blade grips.

ptremb
09-30-2006, 07:36 AM
I rember hearing of someone else that was having a similar issue as yours.turns out the bec circuit was overheating causing an intermitant power loss.they installed an external bec(5v parkbec if I recall)and all was well again.
What are you using for an esc,servo's&gyro,this way it may be possible to verify this hypothisis.
Most esc's rate the bec output based on the input,so if you are running 3cell that limits you to 3 micro servos.If you have more than just the 3 hs-55/hs-65(which on a heli you do) and the bec in your esc is rated for only 2A,add in the gyro and possibly a digi tail servo,your past max.

watt_the?!
09-30-2006, 10:32 AM
collective servo's hold well?

have you tried hovering indoors?

id be surprised if it needed a bec for a heli this small...

esc problem perhaps...but bec as a solution....?..

Tim

ptremb
09-30-2006, 10:42 PM
I found where I saw that(it's an esky king),however he already had an external bec.scroll down a little to the section for customer videos and read the caption on the right side
http://www.justgofly.com/tech400dh.htm

essence25
10-01-2006, 11:27 AM
I rember hearing of someone else that was having a similar issue as yours.turns out the bec circuit was overheating causing an intermitant power loss.they installed an external bec(5v parkbec if I recall)and all was well again.
What are you using for an esc,servo's&gyro,this way it may be possible to verify this hypothisis.
Most esc's rate the bec output based on the input,so if you are running 3cell that limits you to 3 micro servos.If you have more than just the 3 hs-55/hs-65(which on a heli you do) and the bec in your esc is rated for only 2A,add in the gyro and possibly a digi tail servo,your past max.


ESC 25A HeliMax (stock) Motor HELIMAX 2580KV (stock) Gyro Align RCE-500X. Servo's 2 X hitec HS65HB (mighty feather) 1 Futaba S3107 (aileron)
1 x HDS-877 Digital (tail).

essence25
10-01-2006, 11:35 AM
Here is what I discovered....


Hovering headspeed measured with my optical tach.

Headpeed below 2100 = The vertical rocking... (also noticeable in forward flight)
Headspeed 2350-2430 = Rock stable hover.

After 8 minutes as the battery gets towards empty it rocks again.
I is mild but noticeable.

So the question is!?.... is this normal? Should I be able to have a head speed of 1900-2000 and and no wobble ? Does this happen to others ? On T-rex etc.. ? Should I stop trying to tune it etc..

I will also check my blade grips washers on the feathering shaft since they are tight with 0 horizontal play perhaps I need to sand the plastic washers a bit so they are not that tight...

And finally what is the optimum head speed recommended for the MX400 pro w/325 mm carbon blades or what most use ?

If 2400 is safe, then I'm all set. I will post pics if anyone wants to see the little bird...

thanks

jjonesfla
11-14-2006, 12:56 AM
I just finished building a MX450 and I am expierencing the same problem with fore/aft wobble mostly during forward flight.

I have expirmented with Blade grip tension aluminum vs teflon spacers, lubricaing the Head dampeners. I have my head tach'd at 2100 RPM, w/325mm CF blades.

jjonesfla
11-14-2006, 01:11 AM
I should add that..... on a day with winds of 5 - 8 mph the problem was noticed. There is no other visually detectable vibration during hover.

Inseminator
11-15-2006, 07:58 PM
Hi There

It may not be electrical, try checking all your linkages. Everything should operate smoothly, no binding, also put a drop of oil on the main shaft and tail pitch slider shaft. Hope it helps