two servos per surface
 

OK guys, i have not posted any questions here for quite some time, but i have been busy building. (101 inch B-25)

I am planning on using "y" harnesses and splitting two servos per control surfaces. when we split two servos from the same signal and power output from the receiver, do we loose any torque because we loose some of the curent IE:6 volts devided by tow?

In the past some modelers have used one single large servo and bell cranks to control two flaps or two ailerons (left and right)

I am planning on staying with the KISS method and using only "y" harnesses. will i have to double up on batteries or something like that?

Thanks again for any help on this subject

Jesse

My last airplane was a Goldberg Yak 54, 77" wing span and used two servos per aileron ( two for the right and two for the left ) I used a Y harness to join the two right and another Y to join the two left. From there I used seperate Rx channels for each side.

I also had split elevators and used an individual servo for each half, bringing both together via a Y harness into one channel on the Rx.

I only used one servo for the rudder and one for the throttle. Another servo was used for the choke. So as you can see, I used a total of 9 servos, all of them high torque/speed digitals, exceipt for the throttle and choke which were standard servos.

Even with this many servos, I did NOT find any problems with voltage drop as you were asking about. I did use a larger mAh rated battery pack. ( 2100 mAh NiMh )

I often add a second battery pack, not because I am concerned about voltage drop, but simply for redundancy, in case one battery fails I have a second to keep my plane's radio system functioning. Its quite simple to add a second pack, just use another switch harness and plug it into an open slot in the receiver and plug the second battery pack into the switch harness. This does NOT increase the voltage, it stays at 6.0 volts. What it does do is increase the total mAh rating in the system the sum of the two packs thereby giving you more flights per outing.

So go ahead and use a couple of Y harnesses. Its not going to cause you a problem!

Re: two servos per surface
 

Unless you are crazy careful or use programable servos, they will bind against each other. IMHO if you are not using a programable sevro with y harnesses you are asking for trouble. There are a lot of other options including matchbox's and power boxes. Again IMHO I want my planes to fly the best they can while minimizing potential failures. One potential failure in this case is the servos binding and sucking you batt dry faster than you can say failsafe among other things.
"KISS" is good but "cheap out" is bad
My .0002 cents

If the 2 servos are mounted seperately to the control surface, and a ways apart, it shouldn't really cause a problem. With ganged servos, it would, but if you had 2 on an aileron, spaced apart, it probably any notable binding.

Increase the Mah of the battery, the voltage in a y harness is ran in parrallel, and the voltage stays the same.

Have a look at Matchboxes, they are around $200, and are designed to do this. It's the new high tech way to do it, and allows you to set up your servos to work exactly the same.

Re: two servos per surface
 

If you are not careful, two servos on the same surface can indeed fight one another. The two linkages on the two servos in tandem, need to be set up in such a way so that they do not bind. The geometry may then end up slightly different, but the binding is then gone. Its a bit of work, but it can be done in most cases. If the two servos are way off in their travel characteristics, try substituting for another servo that is closer.

Ive used this method when setting up 3 servos on ailerons using a 3-y connector with good success.

Hope that helps. :)

Re: two servos per surface
 

just curios but what kind of control horns are you using to do this? I have helped with setting it up with rocket city type and a watt meter but not with standard type control horns.

I agree with the last couple posts, unless your carefull you will cause some serious problems running 2 servos per surface withought programming them. You will have to be dead on with your geometry which will be very hard with non programmable, or servos not used with a matchbox. Once you program the servos then you could connect them with a Y, even though it isn't the ideal it would work fine.

Good Luck...

Thanks for all your replies guys. just as i suspected, i will not gang up my cheaper (less torque) servos per control surfaces, instead i will use one per, good quality like hightec bb suported servos and y harness from the receiver. now keep in mind that this b-25 is very long to the aileron wing tip are very far appart, and will also require servo lead extension. I will go for the greater amp battery pack like i did in my helicopter, simply because these servos will draw more curent everytime i move the sticks.

The nick zirolli plans call for the use of regular servos everywhere, but 9 in total. I was hoping to keep it simple by using high torque servos in the tail section, with push rods and bell cranks.

I will take a couple of pics this afternoon and try and post it on here so you can see what i am into.

sure you all know what the b-25 looks like, but i'm worried about the weight and mass of this plane. it won't have extra servos working things like lights or bomb bays or turrets.

again, i'm keeping it simple.

so to summarize, if i got you guys right, i will have to get a bigger amps battery and y harness from receiver and one servos per surface only.

It's not that i don't like the new technology but i have never used a matchbox or a power box in the past, and would not know how to set them up anyways.

thanks again for your replies

Jesse

Re: two servos per surface
 

Rocket City hardware :rock:

Jesse,

If Nick Ziroli is calling for more then one servo per aileron. best to listen to him.

The above post did not say don't use two servos per aileron they just said make sure you set everything up right. As Mike said you can mechanically get everything right without haveing to go to a matchbox or such.

BTW you can get 2 x matchbox from Hobby Wholesale for only $129.99 so they are not as expensive as was quoted above.

If you do go with one higher torque servo you are going to have to stiffen the aileron somehow as I am sure it will twist with only one servo on it. Again Nick knows what he is doing when it comes to airplane design. :D