Talking with Steamboat Phil and NoMustang Mark at Alford, a few weeks ago, I mentioned that I was thinking of changing the steering arrangement from servo horn drive to drum drive - using a one turn sail winch. Their advice was: "If it ain't broke, don't fix it". If I had taken heed, it would have saved a lot of time and money!
The motive for making the change was that it is a bit fiddly to set up without getting slack in the "non-pulled" length of chain, especially at the extremes of rudder travel. The two bottom pulleys are adjustable for this purpose.
View from rear:
and the side:
I purchased a sail winch (£17 inc. postage) and set it in the original "test bed". It was going to need a drum of about 15mm.
It soon became apparent that this diameter was going to be critical and maintaining taughtness would need the same arrangement that I had already. Introducing springs did not help, which was disappointing because they work in the boom swinging mechanism.
So: Project abandoned. If Steamboat Phil and/or NoMustang Mark offer you advice, take it!
The other thing I've had to re-visit is maintaining gentle tension on the secondary line attached to the boom.
The prototype worked well:
as did the purpose-built block, seen to the right of this picture:
With the advent of the central servo to swing the boom, however, it needed moving a fair distance to starboard and this led to unreliable operation.
So, undaunted, I decided I needed a high ratio double pulley-wheel, as used successfully in maintaining tension in the lateral boom lines.
Problem: How do you make one of these?
I don't have any 28mm round stock (or a local supplier) and even if I did, I don't have the tooling to reach that deep - so the disc had to be made from sheet. I first tried soldering the the roughly shaped disc to the hub section but it sheared off when I tried to true it up. (Probably because in trying to avoid flooding the hub section with solder, the joint wasn't good.) Thought Oh bother (or something very similar).
Next time round, tapped hub and disc 4BA and this worked but cutting the groove produced nasty noises from the tool (0.6mm wide).
The result works
(currently using a weight pending the find of a suitable spring.)
but I now find the 2.5mm section needs a shoulder on the nearside to keep the thread away from the disc as it is catching on the outer knot!
Making a new hub section is no problem but I don't fancy making another disc. Having put epoxy on the thread before assembly, I'll never get the hub section out in one piece. I'm thinking Oh bother (or something very similar)
Mike