Model Boat Mayhem - Forum

Dry Dock / Shipyard: Builds & Questions => Yachts and Sail => Topic started by: derfledermause on August 13, 2011, 07:02:49 PM

Title: Graupner "True Blue" yacht.
Post by: derfledermause on August 13, 2011, 07:02:49 PM
 Hello goog people,
I have purchased the above yacht and I find it needs 3 servos. The rudder servo is no problem, I am confident that I can find a cheaper replacement, however, on this yacht the sail servo is in fact 2 servos in parallel. I have looked at the graupner part numbers and the first reaction is "ouch" 75 each. So I have looked at replacement servos, as the originals have a torque spec. of 5.0Kg/cm and there are 2 of them, then I need 2 with identical torque (cheaper) or 1 with 10Kg/cm or more. The servos are carried in a specially designed cradle, so I need to find two cheaper ones or one with double the torque but  which will have the same body dimension as a single. This yacht, being of German manufacture, the spec indicates that the sail area is approx. 0.47 square meter. Would you agree that they have over engineered the required torque and I would get away with a less spec of servo?(cheaper).
This is my first yacht and I have trawled the net looking for info on this subject; ie, "A 1 mtr yacht with sail area of 0.5M squared in a force 3 wind needs a servo of 6.5Kg/cm". I have found many sites with info on how to design hulls, design sails and other aspects of yachting, but nothing about the torque needed for the sail servo.
I would be grateful for any advice and if this information is indeed on the net, then the net address would be welcomed.
Thank you,
regards,
derfledermause.
Title: Re: Graupner "True Blue" yacht.
Post by: grasshopper on August 13, 2011, 07:36:06 PM
Try looking at servos designed for model car usage instead of 'proper' sail servos - nitro model car servos have massive torque figures  for steering purposes - all built into a standard case size.

Some of the names to look out for are ACE, SAVOX and the latest name on the block is ALTURN, try looking at this one

http://www.logicrc.com/?ItemId=P-AAS750MG&s=c:0,c:50,b:Alturn

and all for less than 20 - just make sure you mount it well, try and fit it without it ever getting stalled at either end of it's travel and use a decent 6v pack to power your radio to benefit from it's power, not a 4 off dry cell Rx pack, they can pull a few more milli-amps than a 'standard' servo
Title: Re: Graupner "True Blue" yacht.
Post by: derfledermause on August 13, 2011, 08:04:42 PM
My apologies, I have just found this site that has the calculations needed. Thank you grasshopper for your informative and prompt reply. Now back to the calculations.
 http://www.joliebrisemodels.co.uk/tenth/servo.html
Thank you,
derfledermause.