DX7 Trim Tip

[Jermo]

Unless you want to setup trims for all 4 modes take any trim settings out and add them back in the subtrim menu. Subtrim is global to all modes while Trim is mode specific.
Jermo

[vrwired]

I am not sure Jermo, is what you said conflicting?... maybe it is just me???

take trim setting out unlees you want all 4 modes...

wouldn't that make trim global and subtrim mode specific..

If you are right, you can call me any name you want in your response!

I would deserve it....

[cdrking]

So are you saying after you get a "perfect" mechanical setup to go in and mess with sub-trims? :roll:

Jeff

[Jermo]

So are you saying after you get a "perfect" mechanical setup to go in and mess with sub-trims? :roll:

Jeff

Maybe it's a newb thing to do but if I trim out the bird I don't need to do anything with trim anymore unless something changes. I keep a log of settings and changes with why. Seems to me that a trim is nice to use for changing flight conditions where subtrim is something specific to heli setup. I guess it's up to the individual.
Jermo

[Al Austria]

The problem with that method is that if you had established a 90 degree angle with the servo arm using subtrim during initial setup, you'll loose that symmetry and in an eCCPM machines' case, it simply won't work. Your best bet for any machine is just to trim it out mechanically.

[Jermo]

At low and high stick the swash has the same relationship. I'm not sure what you mean. Adjusting mechanically to take trim out would give the same result (other than the trim number being 0)
Jermo

[Al Austria]

Think about it. If you ever run into a helicopter's setup where servo arms MUST be at a 90 degree angle at a specific pitch setting(0 degrees in a most 3D heli setups) in order to minimize geometrically induced interaction, subtrim is only used to set the 90 degree angle and NEVER touched thereafter. Adjusting subtrim after establishing a 90 degree(or whatever angle) will result in the arm moving off that preset angle which in turn will cause assymetrical movement(differential) of the arm.

Adjusting mechanically to take trim out would give the same result

Wrong. Adjusting the links will not cause servo differential.

[DavidH]

It is best to set eCCPM up mechanically correct if at all possible. Do not use sub trim or trim. When trims are use the electronic center of the servo is offset. Some of the times that can screw up the geometry and how the eCCPM should operate.


David

[Jermo]

It is best to set eCCPM up mechanically correct if at all possible. Do not use sub trim or trim. When trims are use the electronic center of the servo is offset. Some of the times that can screw up the geometry and how the eCCPM should operate.


David

Let's get back on topic. Nobody is saying to setup eCCPM with trims so stop with that.

After the heli is correctly setup statically for eccpm ..ie mechanically/tx interactions tuned out..etc..

Generally when you fly for the first time you end up trimming the heli for flight. Is this not a correct statement? As a result you are either required to duplicate the trims for each of the 4 modes OR can just add them to the current subtrim settings.

Jermo

[DavidH]

Generally when you fly for the first time you end up trimming the heli for flight. Is this not a correct statement? As a result you are either required to duplicate the trims for each of the 4 modes OR can just add them to the current subtrim settings.


I don't use trims. The models are trimmed mechanically. If the model is trimmed electronically for straight and level flight. When it is pulled vertical it will dart off in the direction of the trim unless the swash is neutral. I have always had the swash neutral with no electronic trims. This is on eCCPM models and mechanical mix models. Been doing it the same way for 10 plus years as I was taught by a couple of World Champions.
Horizonital fin placement, C/G of model, fly bar ratio, rotor speed all determines how the model flys. I adjust those and leave the swash neutral. When I was flying mechanical mixed models, I flew 3 models off the same program in the radio. They were all mechanically matched to the electronic program in the radio.

David

[Jermo]

David,

1. leave your credentials and stuff at the door.
2. explain things differently, remember your audiance..ie new

I don't know about your heli but when I get mine 100% square and level I have to hold stick to keep the heli in one spot. To get hands off hover I have to apply trim. From my reading this is 100% normal. Are you suggesting that you don't trim for this at all? If you adjust mechanically then you alter your ccpm interactions and end up compensating electronically. If you adjust with trim you achieve exactly what I'm saying anyway.

Please try to explain this.
Jermo

[DavidH]

Maybe a Trex 400 series won't sit in one spot in a hover with no wind without input.
But a 30 size and up model can be setup to hover virtually still without input.

Yes all my trims are set to 0 or neutral. With no wind the model will sit still without input. What I call still is that I can take my hands off the transmitter and it will sit there for 10-15 seconds before it starts to slowly drift off. And if it is dead calm, the drifting is caused by the ground effect draft. This is fairly simple to achieve.

When you get into forward flight, you will find out why it is important to have the swash neutral and everything set up mechanically. Forward flight has different aerodymanics than a hovering model.
Don't know why I should leave my credentials at the door. Just letting others know I have the experience to back up what I am trying to explain.

David

[peterob]

I think the issue here is that subtrim applies to single servos, while normal trim applies to swash mixes.

Adding subtrim to the aileron servo is not the same as applying trim to your aileron mix.

[flingwing403]

ok so I'm not trying to pick sides but just offering a newbs perspective here.

you dave are correct in the fact that a micro heli doesnt inherently want to sit still even when perfectly trimmed mechanically. i may be new to rc but having a mechanical background i am a huge fan of making everything perfect at set-up prior to doing anything with the radio, so before i even turn a rotor my swash is dead level and i make sure every thing is in line, paddles flat and equally spaced from mast, heck i even make sure all ball links are perpendicular to the ball, this sometimes means a lil twist to make it look purdy if both ends arent on the same plane...call me anal, i just like a perfect setup.

maybe it comes from knowing that if my AME turns a screw a bit too much in the hangar my day at work could involve much more effort to hold still (full scale)

but i have friends who fly bigger birds (nitro) and i watch them let go of the remote, take a drag off theire cigaretter, and go about flying like it was nothing.

well lemme tell ya the lil t-rex just aint like that, i got the thing so perfectly set up and in a huge indoor enviroment with zero wind i'm lucky if i can let the cyclic thumb go for a max 3-5 secs before she starts to go I am quite lucky..and when i say starts to go i dont mean drift i mean catch her now or shes toast...

now back to comparing with full sized helis and to stop the back and forth with you two based on completely different machines.

I am certain you have both heard of gyroscopic prescesion as well as all related effects to have a quickly spinning mass attached to an object.

so needless to say your nitro bird whose weight is measured in pounds WILL be much more stable and resist such urges to wander on its own as opposed to a heli whose weigh is measured in ounces.

so to sum up i think your both trying to say the same thing

-set the bird up perfectly neutral mechanically as per manual

difference happens when dave flies his bird sits like a rock

when we t-rex guys fly we have to hold her where we want

and i think all jermo is saying is that if you find yourself putting a wee lil trim input to prevent constantly "thumbing" it then maybe add it in sub trims instead

I myself however will keep my sub trims solely for mechanical neutral and use flight trims if needed for a lil compensation because flying influences will always vary ie wind weather humidity or altitude( i"M pushing 5000'asl outside my front door)

and if i use my sub then go fly elsewhere i may find my lil bird all out of whack and wonder why..

now that all the children are getting along lets go back to flying ;)

[spork]

ok so I'm not trying to pick sides but just offering a newbs perspective here....
now that all the children are getting along lets go back to flying ;)

Wow, that was hardly condescending at all.

[DavidH]

Flingwing,
Yes I have flown a Trex 450 that belong to others. Some of them were setup fairly well. Even at that yes they are what I would call squirrely in a hover.

i may be new to rc but having a mechanical background i am a huge fan of making everything perfect at set-up prior to doing anything with the radio, so before i even turn a rotor my swash is dead level and i make sure every thing is in line, paddles flat and equally spaced from mast

That is exactly what I do. I leave everything in the radio defaulted. Only get the controls operating in the right direction. Then I set the model up as mechanically true as I can set it. There is a difference in how models that are set up this way fly from from models that are set up using the programs in the radio.
The model in a hover while taking a drag off a cig is good. I have seen couple of pilots have the model in a hover and use a tach to tach the rotor rpm. They have the tach on and place it between there knees to hold it. Get the model up in hover and stablize it. Then grab the tach and check the rpm.
I try to make the model fly itself as much as I can. Saves me from having to fly it.

Only point I try to make is for pilots too use the mechanical setup and not have to rely on the electronic setup. Even rebuilding after crashes it is a lot easier to get the model back to what it was before the crash.

David

[flingwing403]

spork wasnt trying to be condescending at all and when i reffer the the "newb" i was implying myself seeing as i have only been in rc less than a year, which was mentioned in my greeting post elsewhere.

as for the children comment it was purely humour and to lighten the mood as it seemed it was working its way towards "tense" however i come to realise that humour or sarcasm doesnt always come out the same way in print as it sounds in my head..

so if i offended anyone with that previous comment than my appologies

[BravoSlicker]

1. leave your credentials and stuff at the door.
2. explain things differently, remember your audiance..ie new

Hey Jermo,

Did you see DavidH's title? That comment was like correcting a teacher in class who has many willing and able students to teach. Remember, your new - he's not and we're not in the Trex 450 section, so all experiences are welcome.

BravoSlicker

[Al Austria]

It's apparent to me that Jermo has no concept of mechanical trimming and its benefits vs electronic trim and its problems. And yeah, DavidH is knows his stuff.

[spork]

so if i offended anyone with that previous comment than my appologies

Nope. I probably took it wrong. I'll check the dates on my meds and try and chill.

[Jermo]

ROFL....flingwing403, I didn't see anything condescending in anything you wrote.
Anyway my point about leaving your creditials at the door was more a comment of explain it to me rather than try to impress me. I'm old enough to know that any idiot can claim to be a rocket scientist but only someone who actually has the training can explain it correctly.

Flingwing403 made my points. It seems the difference all come down to personal preferences since nobody has actually explained this in a way I understand.

100% mechanically level and square my T-rex won't hover, it pushes left(left from memory, I'm at work, picture the heli nose in and it leans left) to get it to stay in one spot I have to give right aileron (or just trim it out)..

Ok..so let's say I land, center the servo's, measure the movement and mechanically adust pitch and aileron to take the trim back to 0. Will that not affect inverted flight and ccpm interactions..etc? will my swash now not be level?

Jermo

[BravoSlicker]

Ok..so let's say I land, center the servo's, measure the movement and mechanically adust pitch and aileron to take the trim back to 0. Will that not affect inverted flight and ccpm interactions..etc? will my swash now not be level?

I'm gonna go out on a limb here and guess that when your inverted, your not going to take your fingers off the stick to take a "drag off a cig". Once inverted, your dancing on the sticks and getting ready to pull off the next maneuver. Any slight trim differences between upright and inverted aren't really that noticable.

[DavidH]

I'm at work, picture the heli nose in and it leans left) to get it to stay in one spot I have to give right aileron (or just trim it out)..

Now I understand, your trying to trim the heli to be level in a hover. Will never happen. When a heli is sitting still in a hover it is going to lean to the right if looking at it from the tail. This is due to the gyro scopic procession and the rotor system creating more lift on the advancing blade. Also when the heli leaves the ground it wants to go right for the same reason. That is why you see contest pilots shim the landing gear.
http://www.ronlund.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=heli&Product_Code=FMP1002

The above are installed on the landing gear and tilt the heli so the heli will come off the ground straight up without adding left cyclic at liftoff.

Here is a link to some great information. It is questions by modelers and they are answered by one of the best in the business. I learned a lot from him by having the privledge of competing with him and seeing how he does things. He will always answer questions.

http://www.curtisyoungblood.com/faqs/

David

[BarnOwl]

Jermo, a T-rex 450 will NEVER sit stable in a hover without moving the sticks for more than a nanosecond......No matter how well setup or how badly compensated by trim.

[flingwing403]

Jermo, mechanically straight and level or not a heli ,by nature, is inherently unstable and doesnt want to fly, thus all the ongoing jokes about us pilots beating the air into submission. as dave and i mentioned with gyroscopic effects your heli will "sag" to one side, same with full sized machines, and the side is dependant on which way your rotor turns, since ours go clockwise the advancing blade on the left will generate more lift thus your right skid will hang lower, again this is aerodynamics and not a swash plate issue, if you start trying to trim out swash in order to fly dead level.....well......lemme know how that goes :glasses2:

guess you'd have more luck placing weights on the left of c/g in order to "balance it" but now where getting into full sized talk.

so in the end the set up stays level, if you touch nothing she drifts just by nature of helicopter dynamics, and you the pilot control her otherwise.

just be thankful that rc's spin so fast that we dont have to get into a conversation about "retreating blade stall"...trust me your drift pales in comparison to the carnage this would inflict on rc birds should they suffer from it..