4.8v E-max Servos - be warned!

[Bob Cotsford]

I'm posting this as I've not seen it before.

I'm putting together a Macchi MC200 and wanted the inner wheel doors servo operated so they could be synchronised with the legs. They're not big, let's say 3"*2" each and just light plastic sheet so there's no weight to them. The hinges are free enough so they will drop under their own weight. Simple, couple of micro servos then, one per door. I had some Emax ES08s around so popped them in, hooked them up and everything worked a treat. Legs go up, doors close - doors open, legs come down. Fine.

Did I say I'm using 2S LiFe as I usually do these days?

I'd got the model assembled checking and tidying things, the wheels are up and I'm adjusting the flap movement when I start getting low voltage warnings from the Taranis, then a smell of hot plastic:

I've had servos fail in the past, they've just died by going open circuit but this one went short circuit - the HD switch harness looks similar! Luckily the battery was LiFe and not LiPo so it took it in it's stride, as did the FrSky receiver and S-bus hub.

Now I have Emax midi size 20gm servos on the ailerons of my Tornado where they've worked fine on 2S LiFe for 2 or 3 years but these little analogues really don't like it up 'em, to misquote Corporal Jones.

[Bob Cotsford]

and the switch:

I've removed the back cover off the switch, this is the type with a built in charge socket. I don't remember where I bought it but it's identical to another I've got in a Horizon Hobbies packet sold as a HD unit.

I don't know whether it's clear but it's a 4 pole switch - i.e. it has 4 sets of changeover contacts to switch 4 circuits. Usually these would be wired in parallel in better made switches to spread the load over multiple contacts and to improve reliability. In this case only one pole is being used, there are contact pads around the other three poles but they are not soldered.

Personally I find it a bit scary.