1/4 scale Servo repair - any suggestions ?

[Richard Cohen]

Morning all
I am trying to find out if there is anyone out there who can repair futaba servo's.
The unit in question is a Futaba S3302 1/4 scale servo and rather than purchase a new one, a repair would be preferred as it is only to be used on the tail wheel.
Is there anyone out there who is able to help ? (we are based in Swindon, Wiltshire)
regards

Richard
(Team Mustang)

[Dave Cooper]

Hi Richard

I'm based near Malmesbury, Wilts. Is your problem electronics or mechanical ? I'm currently designing /building a 1/4 scale contra-prop gearbox for my Wyvern project, so this is of interest. I'm not sure what the position is regarding Futaba spares though...I've just located a good supplier of miniature gears /racks if it's mechanical. If it's one of the electronic items - amplifier /decoder etc this will probably mean a direct replacement as they are usually 'non-serviceable' items. How did the fault occur -accident damage, or, did it just stop working ? It may be worth popping the lid off and checking for cracked gears /broken teeth. Also, underneath the gearbox, does anything look (or smell) as if there's been any signs of burning, loose connections, dry solder etc...
Dave

[Richard Cohen]

Hi Dave,
thanks for the reply
unit was working last time we tested everything. One of the other team members took it home and was going to take a look. I might have sourced some spare servo's for parts for another club member but need to get the unit stripped to have a shuftie.
I have to say that the contra prop unit has got my attention. Very fond of the Gannet and its power train. Any photos/construction threads on here ?

Rich

[Alan Cantwell 1131]

what exactly has stopped working on it?

[Dave Cooper]

I worked on Gannets in the FAA - 849 squadron based at Brawdy, S.Wales. Strictly speaking, these are co-axial units due to the Double Mamba's twin turbines /separate gearboxes. There is a beginning thread for my build on 'Your New Projects' but no photos as yet. All my gears are mocked up in wood at present and, am just changing shaft centres, teeth profiles and planetary ratios to get it all running sweetly before ordering the parts in metal.

Coming back to your servo, I think it shares all the same parts with another Futaba model (see Futaba's website) with the exception of the final drive gear which is in metal on yours and in nylon on the other unit. If you suspect it has an intermittent fault (the world's worst !) check first the receiver output using another servo, then trace the continuity of the signal and power supply leads into the base of the servo itself. These conductors are very fine and can be prone to fracture /internal breakdown. Try flexing the lead with a multi-meter in circuit between the plug and the surface mount collector in the base of the unit. It should show low /no resistance at all times.

Good hunting...
Dave

[Alan Cantwell 1131]

is it worth the agro? a cheapo hi-tec 1/4scale would do for a tailwheel, i might even have a futaba 1/4scale i would let go with nylon gears, little used, repairing servos these days is a mugs game

[Dave Cooper]

Alan's got a good point there. What with the price of fuel, postage, etc these days, it may be beyond economical repair. So, perhaps, strip it down for spares.

However, if your model is prone to banging its tailwheel down hard, it may be wise to fit a metal output gear rather than a nylon one which may strip teeth on repeated impact. Alternatively, a nylon final drive gear plus a bit of suspension /shock absorbing, may do the trick !
Dave

[Alan Cantwell 1131]

closed loop to the tailwheel, with 2 stout springs works for me, nice servo saver