Originally Posted by arcdude
I'm truly envious over your gear, fantastic. Do you mill/design them your self?
Yes, all my own work as we used to say in school
. Commercial rudders are what they are, but there's a lot I don't like about them, I looked at the recommended rudder and it's over £40 delivered, which galls me as that's enough material to make dozens of rudders, so a couple of evenings work to get this. I'm going to re-anodise it, I'm not happy with the finish and it's easy enough to fix, I've got to anodise some other parts so I'll stick the rudder in the process. Then I'll be happy with it.
There's a bit of thought in the design. Looking at others there's a variety of bearing arrangements and I went for a 'top hat' bush setup. I've used Delrin for now, but it's easy to make up other materials into bearings for this depending on how this stuff fayres. I wanted to avoid metal to metal contact so a polished stainless pin is held by a grub screw against a flat to retain it, but mostly to ensure the shaft rotates in the bearing, not the rudder. The shaft is supported in two places on the rudder side, so there's a large spread of load. It bottoms out just above the rudder blade groove, so that it can be pushed up to remove from below. I've tried to make the bearing surfaces as big and as spread as far apart as I can for this size. I've opted for a push pull control arrangement with a single control horn because I'm using a rigid carbon rod for the link to the servo, an Alturn USA 750MG, so a strong link and servo.
So a milling machine for most of the work, but the compound curved shape of the rudder stock had to be done off-hand on a table disc sander, as did the radius ends in the 'hinge' (don't have the right sized cutter), and a lathe to make the pin and bearings. Apart from the lathe work this could have been reasonably made using hand tools and a drill.
There is one more part for the rudder to come which I've not made yet, which is a simple load spreader. All of the strut rudders I've seen use angle brackets to bolt to the transom, this spreads the load. Mine is the strut arm straight on to the transom, so I'm putting in 'fitted' studs which will locate through a plate inside the transom, so effectively those side loads on the rudder will be transmitted to the internal plate hence spreading the load on the other side of the transom. It'll give me a neat looking butt end and reduce sealing needs a lot.
The important bit, the blade, was one of a variety of Carbon/Glass layups I've been playing with. It's seriously rigid and profiled to reduce drag. The wedge rudder thing does my head in and I've not seen any science behind it, proper sections for me. From a sheet of laminate it takes about 15 minutes to make a rudder, so a total loss is not a problem, and it does seem that the carbon dominant surface gives me nice friction levels without much wear, I've cycled the rudder up and down hundreds of times and it feels the same as when it went in. With water present friction does not change. Currently the blade is known to be too big, a junior hacksaw and a Swiss file is all that's needed to tweek it down in the field.
I'll be using carbon for the turn fin, but that's a complete unknown to me so that's gonna be fun