retract servo vs digital servos

[Marko]

Hi all whilst I'm building my spitfire wing I'm now looking to install the retracts . I'm building the Brian Taylor 69" off the plan and using unitracts mechanical units , but what is the benefit of using a dedicated retract servo which isn't proportional against say a normal one which is any views on this would be great
Cheers ....... Mark

[Danny Fenton]

Hi Mark, I will probably get shot down for this, But for my Nijhuis Spitfire which is around 72" I used a std but strong analog servo on each leg. This way you can use endpoint control and servo slow to make setting them up fairly painless.

Don't worry screws were fitted to the servo arms

Cheers

Danny

 

Edited By Danny Fenton on 13/10/2013 23:26:22

[Marko]

Hello Danny lm glad you answerd first your straight to the point thats exactly what l thought the servo setup you have is simple cheers lve got some in mind l can use
cheers again ......mark

[Chris Bott - Moderator]

The whole point of a retract servo is that any loads applied to it at either end of travel are transmitted in a straight line, directly through the bearing. This is either landing loads which can be considerable, or just the weight of the wheels during hard manoeuvres. If using a std servo and adjusting end points, these loads may well have to be taken by the servo gears.

In practice, whether this is important may depend on the retract design. If the design means they lock at each end and the loads are removed from the actuating mechanism, then the above may not apply.

[Martin Harris - Moderator]

Certainly, every retract unit I've had any dealings with has had over-centre locks designed into it so there shouldn't be any load applied to the servo in the up or down positions.

The 180 degree movement of a pukka retract servo is still a very useful feature. Apart from the mechanical advantage assisting with retraction loads as the weight of the wheels are acting through a an decreasing mechanical advantage, it also means that with the required set-up there is very little linear movement per degree of rotation meaning that there is some latitude with the travel required to lock the retracts correctly- very important in pre-end point adjustment days where the set-up was entirely controlled by the linkage geometry.

There's no doubt that a modern digital servo can be selected with the necessary grunt - just watch for stalled servos as the current draw may be quite significant!

Edited By Martin Harris on 14/10/2013 09:07:28

[BrianB]

Check out the Spektrum A7000 retract servo.Very powerfull servo which is analogue,can be used with servo slow and accepts end point adjustment.Reasonable cost too,bought one last week from Kings Lynne Models for £16-50 plus reasonable post & packing.I plan to use this to work my Unitracts retracts on my 72" Spitfire,initial tests were spot on,lifts and lowers both legs without any problem.

Edited By BrianB on 14/10/2013 10:49:50

[Marko]

Hi all thanks guys for your replys as I've never used a dedicated retract servo I wasn't sure of there advantage !! you have all made good points cheers .one more from the daft question dept , would I need one servo per wheel ??? as in Dannys pic/vid ta very much ...... mark

[Bob Cotsford]

With a one-piece wing and straightforward pushrod layout one servo is usually enough. I used two for my Crescent Tornado before I swapped to electric retracts, but only because one was in the wing and the other in the nose for the trike U/C. My WM Super Chippie and H9 Texan both use one central retract servo. The load is balanced across the output shaft during raising and lowering with this setup.

[Danny Fenton]

I used two servos so that I could adjust each one individually. They are not on a Y lead they are on a mix.

Cheers

Danny

[geoffrey cowpland]

I have just installed an elecrtic retract system in my DB Sports and scale Spitfire and they work very well and are very neat and light. No hydraulics or air bottles requred! I bought them from Electron-retracts which is a Spanish company but speak English. The only problem was that at that time they did not supply Oleo legs so I had to get them elsewhere. I understand that the company is now supplying the legs.

Regards

Geoff

[Marko]

Thanks guys for all your responses I'm off to unitracts in the morning as they make a set for the Brian Taylor spit !!! I've heard they take a while nowadays cheers all .......... mark
Geoffrey do you have the web address of yours ????

[Martin Harris - Moderator]

Posted by Danny Fenton on 14/10/2013 15:32:33:

I used two servos so that I could adjust each one individually. They are not on a Y lead they are on a mix.

 

Nothing to do with playing with the sequencer in your DS-16 to get a nice asymmetric scale retraction Danny?

Edited By Martin Harris on 14/10/2013 21:59:05

[Danny Fenton]

Hi Martin, no before I became a Jeti night The force is strong with the new gear, shall I do the mix in the Tx or the Rx?

[Martin Harris - Moderator]

Ah, a choice in the settings there is...

I've only ever set servo slowing on the receivers (pre-DC-16) but thanks for asking the question (even in jest)because I hadn't realised I could programme this from the transmitter! I should have known that this would be configurable - everything else is!

I think it's much better to do it from the transmitter - that way the receiver could be changed or used in a different model without any extra work.

May The Force be with you.

Edited By Martin Harris on 14/10/2013 23:12:14