[dwb]

I was wiring up my fourth SwitchPilot servo today and ran into a problem - as soon as I hit the "Go" button to switch the power back on, there was a lot of servo "thrashing" and the short circuit protection kicked in. If I disconnected either all the servos on the fourth SwitchPilot or disconnected it, everything was ok.

After eliminating wiring, wire length and the connector, I came to the conclusion that it was time to provide separate power to the units rather than track power. This is advised in the manual for "larger" layouts but I am somewhat surprised that adding a fourth unit would be push it over the edge.

Fortunately I had a 16AC feed available and wired round the layout, I just haven't used it before. Once I separated the power and track feeds to the fourth unit, the start up problem went away. I have now separated the power and track feeds to the other three SwitchPilot servos.

The servos I use are Tower Pro SG90. I guess they must be hungry little beasts when you fire them up.

So if you suddenly find all lights flashing, servos thrashing and then the short circuit kicking in, perhaps it's time for you to separate the track and power feeds too.

David

 

[Richard Johnson]

***That's very good advice - there are limits to what a power bus can cope with that come well below the system limit when turn-on peaks are involved.

Richard

 

[Suzie]

TowerPro SG90 servos take well over 1A each when they are moving, you have sixteen of them so you were rather pushing it running all of that lot from the track, it was probably trying to draw around 20A. It would not be a huge problem were it not for the 'feature' of the Switchpilot which causes all of the servos to move at startup.

 

[dwb]

QUOTE TowerPro SG90 servos take well over 1A each when they are moving
They look so small and cute you wouldn't believe it of them

. I guess you get what you pay for...

QUOTE It would not be a huge problem were it not for the 'feature' of the Switchpilot which causes all of the servos to move at startup.
I wonder if the V2.0 SwitchPilot servo has improved on this?

David

 

[Julian2011]

Hi David,
A visit to have a chat with your local R/C Model Aircraft shop, for a chat about Servo sizes and performance, might be a good idea. There is quite a range to look at, so it might be good to take a set of points with you, so the Shopkeeper can see the range of movement and pull strength required.

There won't be many that can't pull a set of points, if the Servo Lever Arm is kept short and using the inner holes.

You mentioned "Getting what you pay for" and this is often the case with Servos but there are some good little bargains out there too.

J

 

[Suzie]

The little SG90 is sufficiently powerful to snap off it's own end stop (don't ask how I did it). You are unlikely to find a servo that will not be powerful enough to move a point.

 

[Julian2011]

Totally agree Suzie,

There are some Servos which are for Micro Planes but those wouldn't really be in for consideration.

Out of interest I went foraging in the garage to see what size the small ones I have used, turn out to be.

I used them on 2 models, this one is a small Multiplex Fox, converted Chuckie, weighing in at 2 3/8 oz [ 68 gm], for the whole Glider including 4 x Servos, Controller and Battery.


DSC_0669 by JulianR 2013, on Flickr

A closer shot shows the size of the Servos to be 18mm x 7 mm and about 13/14mm deep


DSC_0670 by JulianR 2013, on Flickr

I have also used 2 x the same Servos on a much bigger, very Aerobatic one, where the Servos each haul big deflections on 17" [ 430 mm ] x 2" [ 50 mm ] full wing width, Barn Door Elevons.

Not only are they very small and light, as in the Fox but those big Elevons need far more power than is needed to pull a pint point.

Perhaps when I mention that one the most popular launch methods is to hold onto a wing tip, as far behind your back as you can reach; then spin it round your body, in a rising motion, whilst rotating the body in the same direction
- that sound familiar? - yep just like a Discus thrower!! ..

The Servos have to be able to keep full control throughout the launch and also during fast manoeuvres following long steep dives. Note that for control speed the outer Servo Arm holes are used, not inner as for Points.
[Ever felt the Wind Pressure on your hand out of the car window at 60MPH? - these things will go faster than that!]

PS. These are not the smallest by any means, but your local Aero Model Shop should have much more up to date information.

J

 

[dwb]

Thanks for the info.

I had a look at the manual for the ESU SwitchPilot V2.0 yesterday. There appear to be some power options for the servos, including power off when not moving. I don't know if this would help at power on. Checking on Modellbahn Lippe suggests this is now the only option; the V1.0 is not being offered, so it looks like my next one will be a 2.0. I don't think I'm going to need the additional end stops...

David