Hover bobbing up and down (Head/swash slop the cause?)

[xStatiCa]

I am trying to find the cause of my MX400 Pro (eCCPM conversion) bobbing up and down when there is no wind. It can also get very touchy sometimes when decreasing the throttle stick by just a hair. I checked the swash plate and it has some slop to it which seems to translate into about 2 degrees of slop in the main blades. I got that value by holding the flybar and very very lightly trying to push on the main blades(pitch).

Could the swashplate be the problem? Can anyone think of anything else? I have heard that low head RPM might cause that too but changing throttle curve from 80 to 75 for mid stick did not seem to make things worse(Maybe ill try 85% next time). I currently have it set to 80% throttle at mid stick. This is with the default 2580kv HeliMax motor.

Any ideas? The MX400 simulator on G3 Expansion1 is sooooo much easier to fly because it does not have any of this random sensitivity issue.

[Thorimmortal]

Is your speed control running in Governor mode ? what set up are you running ? motor ,esc, pinion etc. I have been working on four different mx 400's and haven't yet seen slop in the swash , but i wouldn't doubt it , what other aluminum parts in the head do you have ?

[Thorimmortal]

by the way don't get too excited cranking up the throttle curve , especially if your still running plastic parts , do you have a tach?

[Raven_darkcloud]

Sounds like head speed to me. If you are in gov mod like thor said then that can ghange head speed alot.

[xStatiCa]

Motor: HeliMax brushless 6pole 2580kv
ESC: HeliMax 25A (non gov mode as far as I know because throttle curves were setup when
bought used). I have yet to find an official manual for the HeliMax 25A ESC so I don't even
know how to check it. I tried contacting HeliMax and they sent me a manual for a non
brushless electrifly ESC. I have yet to contact them again.
Normal Pitch curve: 35 / 50 / 100 ( equates to pitch of -3 / 0 / +10 )
Normal Throttle curve: 0 / 80 / 100
(**Only using normal mode... but idle up is 0 / 50 / 100 and 100 / 80 / 100 respectively )
Aluminum parts: swash and main hub (Just installed aluminum main hub after last crash but it was
doing this before then.

Hovers around 3/4 thottle.

The bobbing is not really an up and then down(or reverse movement). It just goes down real quick or up sometimes with a very slight movement of the stick and other times it moves down gracefully.

Btw... the play in the swashplate is a vertical movement of the inner part compared to the outer part which is where the bearing separates them I would assume. The heli has been crashed a few times before I got it and I have crashed it 3 times so I was wondering if the swashplate life has run out.

[Raven_darkcloud]

Ok that motor is on the whimpy side from what I've seen. maybe go to a larger pinion. Also Ive found that a pitch of -3/0/+9 works better in normall mode. I think if you change that curve then you will get less jumpy ness from the heli.

[xStatiCa]

Thanks for the info. I was thinking about that last week but I was hoping to keep Idle-up and normal mode the same above mid stick so that when I transition to idle-up mode sometime in the future I will already be used to the throttle and pitch curves.. Maybe that is the wrong thing to aim for though?

I will give your advice a try and change normal mode. I will cut the pitch down to 8 (recomended in the manual for starting out) which will give a smoother transition in the upper half of the stick. I will also reduce max throttle the same amount. If nothing else it will be interesting to see how it handles with those changes.

I don't think this is it because I could have sworn that I was not moving collective or rudder during some of the bobbing but I wonder if what is happening is that I don't realize I am giving rudder adjustments which is also moving the collective. With the collective being so sensitive a slight movement shows up as a lot.

I will try to pay attention to the rudder/collective during my next flight and then make the changes for the next flight. It is worth trying.

[Thorimmortal]

I had that same motor esc combo on the pro , the esc didn't even work new out of the box , and that motor is a turd (not name calling just an opinion) I went castle creations and haven't looked back , the only problem i have found with the cc esc is that the gov. mode seems to work well with some motors better than others , replace the swash if the bearing is coming apart or if there is movement in the center ball , that ball moving up and down will change your pitch , and make the Helli harder to control. if I'm wrong all apologies and disregard this transmission.
P.S. I included some pics. may help may not , the motor in the pic. runs pretty strong hooked up a watt meter at full th. 300watts , its only rated at 200 but what the hell , more is better than less

[xStatiCa]

replace the swash if the bearing is coming apart or if there is movement in the center ball , that ball moving up and down will change your pitch , and make the Helli harder to control. if I'm wrong all apologies and disregard this transmission.
P.S. I included some pics. may help may not , the motor in the pic. runs pretty strong hooked up a watt meter at full th. 300watts , its only rated at 200 but what the hell , more is better than less

The ball is not where the slop is. It is between the outer aluminum pieces. See the attached pic below. It is just an edited version of your pic and not from my heli.

[Thorimmortal]

how much slop is there ? enough to where you think its going to come apart during flight ? I think I saw the same thing in a trex forum some where .

[Raven_darkcloud]

Ya You should not have slop there, my plastic one dont eaven have slop there. Sound like you have a bad bearing in the swash. I didnt catch that you said that in the begining.

[Thorimmortal]

I see in the trex forum finless bob says 2mm in the paddles is normal , and or slop in the swash , a little bit. he also says they all have slop .

[xStatiCa]

Thorimmortal, Unfortunately I have nothing to compare it to. My Concept DX 30 collecting dust in my garage has no vertical play in it whatsoever so it does seem like way to much to me and seems dangerously loose. It is hard to say though because maybe it is normal for these swashplates.

Thorimmortal, how do you measure that 2mm? Should I hold the main blades and try to twist the paddles and measure the ends of them to see how far the ends move up and down from the rotation? If so i is somewhere around 1.5 to 1.75mm.

If I were to guess I would say that the bearings are wearing out/damaged or something. I would hate to order a new swashplate though($37 on towerhobbies) and find out that the play is normal or not a problem. The wife barely okayed the $150 to fix the mx400 from the last crash so another $37 on a hunch probably won't work :).

Raven_Darkcloud, If you hold the main blades on your mx400 and twist the flybar paddles do the two aluminum pieces move the opposite direction than what they are supposed to(vertically as well as rotating horrizontally)? The problem with this is that a lot of movement to me might be a little movement to you(or vice versa).

[Thorimmortal]

pm finless bob and ask him I'm just repeating what i read wouldn't want to steal any ones thunder!

[jrohland]

Because our 400 helis use a Bell-Hiller mixer, movement of the swashplate translates to about half as much movement at the blade grips. This means you can have slop in the swash which will be half as much at the blades.

As such, I would look for slop somewhere closer to the blades. When I had trouble getting my blades to track, I put the heli under a bright light and magnifying glass. I went through every linkage, pivot, bearing and lever in the head until I found the problem.

Do you have the aluminum upper mixing arms installed? These are the arms screwed to the sides of the seesaw. If you do run those aluminum arms, you probably have a problem with a loose inside bearing on one or both arms. See this tread for a mod I did to fix that common head slop problem: http://www.helifreak.com/viewtopic.php?t=13676

Basically, you should not have even 1 degree of free play when you twist your blades (at the root) while holding your flybar steady. If you do have some slop when twisting the blades, track it down and fix it.

Lastly, I am guessing you are using the Spektrum DX6 radio (as do I). If so, keep in mind the sticks on that radio are not great. You may be having problems because the left stick is ratcheted. I put a piece of silicone fuel tubing under the ratchet pawl to get rid of the ratchet.

jrohland

[xStatiCa]

Because our 400 helis use a Bell-Hiller mixer, movement of the swashplate translates to about half as much movement at the blade grips. This means you can have slop in the swash which will be half as much at the blades.

As such, I would look for slop somewhere closer to the blades. When I had trouble getting my blades to track, I put the heli under a bright light and magnifying glass. I went through every linkage, pivot, bearing and lever in the head until I found the problem.

Do you have the aluminum upper mixing arms installed? These are the arms screwed to the sides of the seesaw. If you do run those aluminum arms, you probably have a problem with a loose inside bearing on one or both arms. See this tread for a mod I did to fix that common head slop problem: http://www.helifreak.com/viewtopic.php?t=13676

Basically, you should not have even 1 degree of free play when you twist your blades (at the root) while holding your flybar steady. If you do have some slop when twisting the blades, track it down and fix it.

Lastly, I am guessing you are using the Spektrum DX6 radio (as do I). If so, keep in mind the sticks on that radio are not great. You may be having problems because the left stick is ratcheted. I put a piece of silicone fuel tubing under the ratchet pawl to get rid of the ratchet.

jrohland

rjohland, I have the eCCPM upgrade and added the aluminum center hub. Everything else is plastic in the head(seesaw and mixing arms, etc).

There is a definite 2 maybe 3 degree play in the main blade holders when very lightly twisting them while holding the flybar paddles still. The play in the blade holders movement do look like they are definitely caused by the loose swashplate. The rods/arms that connect the upper part of the swash to the upper mixing arms for pitch control move with the blade holders and so does the upper red aluminum piece of the swash. The bottom part stays stationary because of the loose swash. I attached another pic to try and show that the two red aluminum parts have vertical play where they normally should only rotate horizontally.

Thanks for the info about the dx6 throttle ratchet issue but I had already read about that and made that mod awhile ago.

[Raven_darkcloud]

Look at the bottom of the swashplate to see what part of the assimbly is moveing. I tested the plastic swahes on my 400 and the one I just build and I have no play at all. Look at Finnless's must fix swash section and see if you can do that fix. Also send an email to helimax they might replace it for free. They have great customer service.

[10karer]

It sounds like you have a bad swash plate like I had

Remove the swash from the heli and try to push the center down through the Cyclic ring and see if the bearing comes loose if not then push up from the bottom in the center and see if the center can be pushed out.

If either of these parts move from the bearing the swash is BAD contact
Heli Max.

They made it right for me

[10karer]

:shock:

[xStatiCa]

Well... for an update...

As for the bobbing up and down, I moved the pitch center point on the stick from 0 to about +2 and that seems to have smoothed out the collective stick for me because I have not seen it happen anymore except for when there is wind. I am thinking it was just caused by accidently moving the collective when trying to correct with rudder. With the collect so sensitive it did not take but just a tiny bit of movement of the stick to make the heli go up or down.

I am glad I started looking at things though because I would not have seen the huge amount of slop in the swash plate.

I am still trying to contact helimax about the swash plate looking like it is about to come apart. So far no response to the first email(sent Wednesday) so I sent another lastnight. Strangely I sent an email about 2 weeks ago looking for a manual for the 25A ESC and an automated response came back pretty quickly and they responded within the same day or so with the manual. Maybe they are having email problems or something. You are supposed to get back an automated response within 24 hours but the last 2 emails I did not get one.

One thing to note about the play in the swashplate... Because of the translated 2 - 3 degree play in the main blade pitch, I have to pushup or down on the blade (depending on low or high stick setting) to simulate tension on the blades to get an accurate pitch setting or each setting could be off up to 2 - 3 degrees either way. For the mid setting I just make sure it is set to 0 degrees at the middle of the slop(well i currently have it at about 2 degrees as mentioned above).

[Raven_darkcloud]

Thats good. also try a higher head speed and you could get smoother flights. I'm adding a head speed/pinion calculator (excel format) to the build section.

[xStatiCa]

Still no reply from HeliMax. Looks like thier support email address is not working at all or they are ignoring me.

[Raven_darkcloud]

hmmm, thats odd. I have tried to duplicate slop in my head but all I get is from the links and flex of plastic parts. Try Li chann (ark) Not at home so I can give the exact email right now, but if you chech the site its there. I talk normaly to a guy named Bonbon or Benbon or somthing like that I cant remember but lots of help. if you can get vid of it then I can get a better answer.

[xStatiCa]

I will try and get a video of it but I don't think the resolution will be good enough to show the problem very well. My sony 5mp camera that takes video too does not seem to focus well on close objects. My shapr DV camera would even be worse I think.

When you hold the flybar and very lightly twist the main blade holders it causes the mixing arm rods to twist the top red part of the swash plate in different directions(up on one side and down on the other) while the bottom part of the swashplate stays stationary. That is the movement that translates to 2 to 3 degrees of main blade pitch slop.

I will see how well the video comes out tonight.

[Raven_darkcloud]

I do stand on the piont of, go ahead and replace it. That just sounds like a crash waiting to happen. Then keep hounding helimax about it for a spare.