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Wiring an IOM

Posted: 20 Nov 2004, 08:53
by Jamestj
Hi there!

Since I have posted on this forum before and had helpful replies, please could I have some help with the following?

Small batteries may not be ideal for supplying high currents, say, 6 amps to move the sail winch. Can a large capacitor (say 1 Farad) be connected across it to boost its power?

If I use a 9volt winch and an 8.5 V supply battery (2 cell Lipo), how do I get 4.5V to run the radio?

Do sail winches have battery elimination circuits (becs) built in?
If not, are becs available?

Are minature receivers available which will survive 9V?

Can the negative wires of servos, receiver, winch and battery be connected (grounded) together?
If so, can they be connected to the carbonfiber fin to create a 'ground plane?'

Many thanks

Posted: 21 Nov 2004, 02:01
by Ralph Knowles
Jamestj, Hi there.

Do I detect that you are trying to re-invent the wheel? The power reqirements for an IOM have long been sorted out using three or four makes of winches and servos. I use K Bits modified lever arm Hitech winch and have it fused at 1.62 amp for a 6v supply. There should be no problem at this rating as long as there is no hang up which would overload the motor, then the fuse quickly protects it. I would say that you should forget the Lipo batteries and 'go with the flow' and use five cell 6v system for Hitech, or six cell 7.2v on some of the other makes. Futaba Micro RX runs on 6v quite happily and if you use the Futaba sail winch then it has a step down to from 7.2v to 6v built in to it. I have no idea where your 6amp load comes from. It would need heavy auto wire to accomodate it.If you use a 6v system using the 3/4 size AAA cells and a Micro RX then the all up weight is as good as you will get, and if properly charged, should last all afternoon.

Good luck


Posted: 22 Nov 2004, 00:42
by Jamestj
Hi Ralph

I've never made a model sailing boat before so I guess that I am coming up with some crackpot ideas. Author Spaldi01 was making some enquiries about sail winches, particularly of a Hitec type, and received some replies -

Of theHitec HSR5995T, Lester Gilbet replied

"Incredible specs! With a 6 cell NiCd pack (and "heavy duty" connector cable!):

Operating Speed (7.2V): 0.12sec/60 degrees at no load
Stall Torque (7.2V): 417oz/in. (
Current Drain (7.2V): 380mA/idle and 5.2A at lock
Weight: 1.97oz (62g)"

At 62g this seems incredibly light for a sail servo. My understanding is that his servo could draw over 5amp if put into action suddenly. I am concerned that electrical interference could cause the servo to jump and the 1.62A fuse which you find to be satisfactory would blow. The specs of other sail servos indicate that they could draw even more power.

I only have the manufacturers figures to work upon and I dont have the experience to cut corners.

Could you sugest a small drum winch, about 3-4 turns which could be used in an IOM?

Many thanks for the posting.

Posted: 22 Nov 2004, 04:11
by Ralph Knowles
Hi again James,

Have a look in Ken Binks site for a list of Futaba and Hitech gear and also a very good piece about their uses. Note the bit about NOT using the sheet as a vang, this will burn out any type of winch. I have used the Futaba P-S5801 drum winch on my home-built Bantock Kite without any problems and would recommend it to anybody. On my latest IOM, an ISIS identical to the world champs boat, I had the Hitech 1/4 scale Digital arm winch fitted as I wanted the fast action that it gave. Now it will probably have a high amps draw, but this is only at full stall with the digital feedback looking for more movement. If the sheeting set up was such that the winch could not pull in any more sheet, be it due to a foul up or the settings being wrong, then many more than the one and a bit amps that are required for normal sailing would be drawn. These winches have a lot of power and if stalled, they can do a bit of damage to the guts of a boat. Ken Binks has been experimenting with the Hitech arm winch and has come to the conclusion that if the RX arial is exposed above the deck- not much is required- then there should not be any signal spikes to effect the smooth operation of the winch. Mine is high under the foredeck and I've had no problems. Have a look at Lesters site at :- He has a lot of very good information.



Posted: 22 Nov 2004, 14:03
by Jamestj
Thanks for the reply, Ralph.

From the web I see that the Futaba P-S5801 does not seem that heavy at 83g and I note that the turns can be adjusted up to six.

This could be just what I am looking for and with Xmas soon upon us ...