HH and use of trim

[Mike W]

Heya all just a quick question regarding the use of trim with a HH gyro ...Can someone clear this up for me regarding the usage of rudder trim in flight to correct the movement one way or the other or should it all be set up mechanically at the boom servo ... Let me explain ... when i turn on Tx i make sure rudder trim is central then when the gyro has beeped and all ready to go i take off and hover and use the trim to adjust the drift ..... is this advisable or do i need to be doing it at the rudder servo ???.... Am new so forgive my not so technical terms used

[mattie-lodge]

Mike what gyro are you using?

Matt

[warboysastro]

Do not adjust trim in heading hold flight!! The gyro will think that's your new neutral position. Your neutral should be set up on the ground by the linkage.

That info hold true for (I think) all heading hold gyros.

Cheers - Rob

[Mike W]

Geegar ..... the gyro is the standard one that came with the mini pred art-tech AT-EG201..... I set the trims to neutral when i plug the battery in then adjust the trims in hover. Forgot to mention my Tx and Rx are both futaba I changed the Rx after whacking the aerial lead on the stock one so changed it hehe

[mattie-lodge]

Mike,

As warboysastro said you shouldn't have to put in any trim in for HH gyro's

Drift can be caused by any vibration on the model. Does yours have any?

Cheers

Matt

[Mike W]

Nup no vibration i think i prolly need to move the servo on the boom to set it up a little better as i replaced the boom the other day .... was just a curiosity question more than anything else

[demonjets]

Try setting your heli up first like getting the servo in the right place. Get leon on the job. ahah see ya later mike.





www.rcmodelhelicopters.co.uk

[Mike W]

hahah Slim he did lol ..... its only a few clicks off .......... Hope ya feeling better m8e ... and i did not crash this time out lol .... all is well lol

[Rotorhead]

Yeah, all this "dont use rudder trim with HH" is over simplifying it.

That is sound advice IF all your gear is the same brand and designed to work together, or like the more modern gyros its self centre calibrating.

The cheaper/older gyros out there dont calibrate the first signal they get as centre stick, but have a figure pre-programmed into them, eg 1500 or 1520 or ....... us.

Sometimes you HAVE to use rudder trim with HH gyros, for instance I had a JR G550T a few years back that needed subtrim otherwise it would piroette one way constanty.

Now that isnt drift, what it was was the fact that I had a JR gyro and all the rest of the gear was Futaba, now, JR uses 1500us for their channel centre pulse length, while futaba uses 1520us, so that difference meant the futaba reciever was telling the JR gyro that it wanted some left/right.

The only way to correct that is to correct the signal, so by using subtrim I brought the 1520us down to 1500us, which is what the gyro uses as centre stick.

This happens with other gear aswell, some use one standard centre pulse length while others use the other one.

Moving the servo along the boom will NOT correct this, all that will do is make the servo arm push more one way relative to the servo case, the actual tail blade pitch will not be changed, effectively you end up destroying the linearity of the servo movement doing this, the gyro in HH mode will still drive the servo to what ever position it needs to be to hold straight, or what the gyro thinks is straight.

If all your gear is the same brand and its all in tune, ie the radio/reciever channels are all giving out the centre pulse length they should then there shouldnt be any need for trim or subtrim, however if your gear is not all the same brand or its been a long time since your transmitter or reciever has been serviced, then you may need a little subtrim to compensate for the difference.