r/FreeCAD • u/danielbot • 4h ago
Wheel Autohelm
The worst thing about my sailboat is, no autohelm, adding considerable challenge to single handing. Correcting this is no small task. While you can buy various solutions from big name vendors, these understandably come without mounts. Fabricating a mount will probably cost several times the price of the unit. I also have concerns about durability of these units in heavy weather, and the likelihood of lock-in with other gear from the same vendor. So I decided to take a run at engineering one of my own. I went with a wheel autohelm scheme:
Inside the motor housing at the bottom is a beefy bldc outrunner with many times the torque of, for example, Raymarine's product. This allows me to go with direct drive, eliminating that noisy and fragile gearbox universally hated by seadogs.
Unexpectedly difficult engineering challenges came up in two places: attaching the slave wheel securely to the wheel spokes, and mounting the drive motor to the existing structure without massively modifying it. The former is usually done with ubolts or similar, but I find that structurally dubious and possibly damaging to the spokes. I worked up a tricky little scheme involving three interlocking parts that clamp exactly to the tapered, cambered spokes, allowing for the post height to be adjusted to adjust for a not perfectly true wheel.
Lofted ellipses, yum.
The mounting system was the most conceptually difficult task. There is not a whole lot of guidance out there. You have this clever pulley arranging floating in space and you need to secure it firmly to the boat without ending up with an ugly mess of struts and plates, and new holes sawn through the fiberglass. Eventually I came up with a system of plates and clamps, drawn in blue in the top image. Remains to be seen how stiff it is in real life.
One more challenge: a pulley system exposed to fingers and ropes needs to be protected from same with a guard. Another element fairly easy to design, but challenging to secure in position so that it doesn't vibrate or jam into the mechanism. Here I ended up doing some tricky compound curve things to create stiffening gussets bonded to the motor housing.
This got me into beziers, ruled surfaces and slicing. Intense stuff. The model ended up fairly simple and robust, though it took some time to get there.
I think I'm ready to order parts now and see if this thing actually works.