Seawind - Murrells Models

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The Kyosho Seawind is a semi-scale model racing yacht, I chose this model because it will fit in my car easily - it's 1 meter long and 1.8 meters high, with an easily removable mast. The picture to the right was taken after I had finished the assembly but before the final fitting kit was installed.
The kit requires a sail winch servo to move the sails in and out, I chose the Hitec HS725BB servo combined with a high capacity receiver battery (5 x NiMH batteries, 1500mAh capacity = 6v). Note the chart showing the relationship between volts/torque and speed for the servo, it operates much more efficiently at 6v than 4.8, considering the drum may rotate 3.5 times to wind the sails in, the difference in speed is = 1.12 seconds. I also changed the drum that is provided with the servo, to a smaller unit because my transmitter does not have ATV so I can't limit the number of turns the sail winch will rotate when I move the stick, it would pull the sails too tight and stall the winch - instead I made a smaller drum, this causes the sails to wind in/out slowly and needs changing back once I get some radio gear with ATV.

I decided that it was too expensive to buy new radio gear so I designed and made some electronics that limit the sail winch movement, see Servo Limiter in the Electronics section for more details.
The servo limiter goes between the receiver and the sail winch, and once adjusted limits the drum rotation to allow the sails to wind fully in & out without straining the rigging or the winch.
Picture below shows the small drum initialy installed.







seconds per 360 deg rotation



Large Drum Installed

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