Two channels - two servos?

The rule says we can have two radio channels. It does not say anything about what we can do with those channels.

Anyone got any sweet ideas for multiplexing channels or gettings loads of functions out of one channel?

There are companies which make switch units that can give you up to 16 extra channels from the one, but I couldn’t think of what you’d do on a Footy with more than 3 or 4…

Tomohawk. Go and look at the most under-rated thread in this forum - Dick Lemke’s thread on ballooon jibs. If he’s right )and I think he is) helf the problems of Footy hull design go away with a forestay release.

I’m experimenting,

OK, so a backstay twitcher is a 3rd function. I can’t think of a way to have two independently proportional functions ( rudder & sails) and a third (either proportional or fixed) when you have the two channels for the rudder & sails. It might be possible to operate a sailboat using fixed-length controls, like the micro-rc models use, but it wouldn’t be as pretty as being fully proprtional.

BTW, Angus, How was your St. Nick’s Day? Put your shoes out? :wink:

I am fairly sure that with a common or garden ‘V’ tail onboard mixer adjusted to an extreme, you could have one servo move (for example) centre-to-up (stick position) and the other to move centre-to-down. Both would then be proportional.

Quite what you would do with the output I don’t know :rolleyes:


I read Dick’s post on balloon jibs, and thought of it in relationships to our boats. The answer may not be in having other channels, but in how you set up your boat. It seems to me that you could instal a momentary micro switch to be tripped by your sail arm at a downwind position. This in turn could electrify a motor that would serve as a winch to pull the tack of the sail in or out. You might be able to get away with a very small motor too. As the sail out on your downwind tack the wind would help it out and as you come about the motor could pull the sail in as the wind was let out of the sail.

Ok, Idea #2…On your sail servo arm, mount a double pulley. Run a line thru another pulley to achieve a double purchase system and anchor the standing end somewhere forward. The free end can be attached to the jib pivot point. You will need another pulley for it to turn a corner. As the sails are released the pivot line would slacken and as they are hauled in the pivot point would return. Might have to use a good servo for this as the strain on the arm would increase.

Reconsidering that idea… a ‘V’ mixer would require 2 channels to be transmitted to operate it with a normal Tx (transmitter). I was thinking in terms of a ‘free mix’ as available on up market computer Tx’s which would mean that only two sticks were used at the Tx but 3 channels are actually transmitted and received… which would be outside of the rule and therefore not allowed.

Note to self: Must engage brain before switching on mouth.


crazy, but how about a control that let you change the rake of the rig? [505 style] it could just be a ram at the mast step… but it might improve upwind proformance/pointing ablility…

Just to throw something into the discussion, anyone ever seen a Stollery Powerlever? Ideal for high grunt with little servos.

That looks very interesting Angus, I love a bit of wire bending. What would concern me if I am understanding it right is this…

At the sheet out position the ‘ring’ is near the end of the arm for max throw. On starting to haul in, the boat would most likely be starting to turn and that is the point where I have had my Futaba 3003 servo stalled in a good blow.

From approximately 30 degrees to close hauled I have had no problems hauling in as it seems that *the load as you come up to point reduces. So in a way the arm appears to give less torque when the most is required. If it works for Roger though I am able to be pursuaded.

*This from observation on the water only.


Without thinking about it too hard, is this a result of the internal geometry of your sheeting system (don’t shout at me - I’ve changed it on my Kittiwake trial horse and I can’t find the DVD)? Full size on the water experience suggests that the load on the sheet in your hand increases pretty steadily as you pull it in.

Certainly in Footys I think that the geometry of sheet servo arms requires a lot of consideration. I changed your standard design because I can’t resist meddling, but it was pretty sensible from what I can remember. But there are a lot out there whee the guy appears delighted if he gets (roughly) enough travel.

That could well be Angus. In the quest for max. throw from a single purchase system in the confines of a footy hull I do use geometry where the mid part of the pull is at 90 degrees to the direction of pull.

If everyone were happy to take on the rather tricky soldering job required to give us 180 degree servos then I would not do it this way. It is about practicalities again. Typically servos swing less than 90 degrees, I have measured a number of HS-81 mini servos at little over 60 degrees. So that isn’t a lot to play with hence my maximum linear pull geometry rather than max. torque as the sails draw in geometry. What we need is a dedicated 180 degree servo with about 35oz/in torque.

My personal reason for avoiding double purchase systems is all to do with line snagging and designing the simplest and most snag free system I can. Yup, in a race one snag and your done :wink:

I am switching to the HS-225BB which is lighter (10g) than a standard 3003 servo and pulls like heck! (54oz/in)


Mast ram sounds like a good one on the shopping list. What about running backstays? They’d make it so much easier to have a proper bendy mast.

But: rember, it’s all weight and complication!

Here’s the radio layout for Yankee III, which may be of interest. The receiver and the sail servo are hung off the deck. The “Linville Blocks” are semicircles of tubing (preferably teflon, but other stuff will work) trapped between two layers of balsa and foam. The rest of the racetrack sheet, except for the part within the range of the servo arm swing, runs through tubing. All this can be set up and checked out on the bench before installing in the boat. The fairleads are gentle “S” bends out of brass tubing. The receiver is stuck on with velcro and there’s a long lead to the rudder servo which enables the deck to be laid beside the hull for testing.

The deck is removable, sealed with Stik-Tak (which I understand is called something like “Blue Tack” in the UK. This stuff is like a sticky silly putty used to put your kids’ pictures up on the refrigerator and so forth. It never hardens and I’ve soak tested it to verify it’s waterproof. So if something needs attention you just pull the deck.

An added benefit is that the hatch can be kept small enough to just permit the batteries to be changed. In Yankee III the battery box has the switch on it and is on a long lead. It pulls out to change batteries/turn on-off and then is tucked down into the fin keel. The hatch can then be taped watertight. You still get water, “pumped” in by the movement of the racetrack sheet through the fairleads, but even in the heaviest going it’s pretty minor.

I’ve sailed this arrangement hundreds of hours over three years without a glitch.



in my mind [and maybe i am wrong] running backstays and mast rams accomplish two diferent things. the backstays would bend the rig. the ram would rake the rig… maybe we are saying the same thing, maybe not, but i can’t think of a way to senseably [without somehow splitting off and assigning two functions to one channel] adjust the backstays while underway… besides, i use a swing rig, so that would defeat the purpose… :smiley:

raking the mast, [and correct me if i am wrong] up wind would result in [hopefully] improved proformance, while down wind, if you raked the mast forward you could theoretically depower the rig, reducing nose diving. this would obviously have to be adjusted for wind conditions, and in very light air [it seems the sailors lot in life to find more of that than s/he would like] i don’t think it would have any impact at all. but those are my thoughts!

I was thinking more of getting the forestay tight. I love Footy cantillever masts but I always come up against the problems of forestay sag. Discussions with Graham McAllister have ended up with him having some Fearfully Secret developments up his sleeve which improve things a great deal. There is my ‘forestay with shrouds’ idea, but it is complex. It could be that the right answer is to have runners but no shrouds.

And yes, having had R.Stollery explaining the virtues of a swing rig with a Bug 3 rig in my hand, I’m very nearly convinced.