Volantex Compass Robotic Conversion

Motivated by the desire for a compact, traditional sailing boat that I could easily chuck in the car and launch with minimal prep, I acquired a second-hand Compass Volantex DG65-class RC yacht.  The previous owner had assembled it from a kit, but never quite finished the rigging.  So, having completed that little task I took it out for a sail using the included 2-channel RC transmitter. 

This test sail verified it behaved nicely on the water and gave me a sense of how it might behave after conversion to robotic control!  The conversion would involve a few stages:

  • Replace the original RC receiver and battery with a DroneLink motherboard, Power module and LiPo battery
  • Rework the electronics bay to accommodate the electronics
  • Replace the stock hatch with a new 3D printed hatch to house the battery and Compass module
  • Integrate a GPS antenna and 915MHz dipole for the RFM69 radio
  • Create a miniature wind vane using an AS5600 magnetic encoder 

Overall layout:


New Brains

After removing the original electronics, I set about designing a mounting plate that would accommodate the original sail and rudder servos, a V4 DroneNode Motherboard and one of our Power Supply circuit boards:



It's a fairly minimalist design that is slung from standoffs and sits suspended inside the hatch opening.  There's barely enough room for all the parts and I had to make the power module sit forward of the hatch opening to squeeze it all in.  The advantage of having everything up on this suspended bracket is that it is well away from any water that may end up sloshing around the bilge.



The GPS antenna has a very short lead, so I decided to float it on a 3D bracket that sits across the hatch opening:

 

You can see the GPS antenna taped onto this floating bracket to the left of this picture, with the rest of the electronics underneath:



The hatch is a fairly simple shape, designed to be printed upside down with minimal support.  It integrates a little finger notch at the back (for easy removal) and a nubbin at the front that locates into the hatch cutout:




The printed part was sealed with filler primer, sanded down, and then finished with several coats of black spray paint to waterproof it.  The LiPo battery is velcroed to the underside of the hatch to keep it well away from any water ingress and make it easy to access for charging. The external magnetic compass (a CMPS12) is also fixed to the underside of the hatch.



The antenna for the RFM69 is a simple dipole affixed to the front of the mast with some electrical tape.


Wind Vane

Creating a miniature wind vane for a boat of this size was quite a challenge.  I'd previously created several 3D-printed magnetic wind vanes for larger boat designs and for our ground station, but nothing at this scale.  Not only would the vane need to be extremely small and light, but also be mounted neatly onto the existing hull.


The solution I came up with was a pair of lightweight printed truss arms mounted to a transom plate.  Here's the transom plate and one arm shown for clarity:
 

The transom plate was glued to the back of the boat with Guerilla glue and then the truss arms were screwed on with M3 bolts.


The wind vane itself is sized around the popular AS5600 module you can find on eBay, Amazon, etc for a few pounds.  The upper part of the wind vane housing contains a tiny bearing (MR84-2RS) and a bolt as a pivot.  On the end of the bolt is glued the magnet.

The wind vane itself has an M3 bolt and a couple of washers screwed into the front end to balance it.  The vane itself is a piece of 1mm clear plastic, cut and glued into the printed holder.






The lower section of the housing contains an upside-down AS5600 module, glued to the inside and sealed with waterproof electronics sealant spray.  Ideally this would be potted in epoxy, but I haven't got round to that yet.  






Performance

We've only had a chance for one proper test sail so far, but that came with lots of learning.  A brief summary:
  • The hatch seal doesn't work - the boat had at least an inch of water in (and yes, I remembered the drain plug)
  • The wind vane tail is too small, when the boat is heeled it no longer catches the wind reliably
  • The radio system worked well - we had connection to almost 200m with an omni-directional base-station antenna - hope to better data rate and longer range with the Yagi antenna tracker
  • The CMSP12 compass appeared to perform very well during calibration and the first 10min of sailing, then it seemed to lose heading completely and by the time the boat was recovered, it had drifted by over 100 degrees.  Extremely disappointing and must be resolved before we can sail again.
  • The power system worked well - the tiny 860mah LiPo still had plenty of charge after an hour of testing and on the water sailing
  • Sheet trim was pretty good
  • Rudder response was good
  • Downwind performance was better than expected - should update the polar to match (needs more of a rounded bum!)
Overall, I'm actually very pleased with the initial build and am confident she'll be an excellent sailing testbed once the teething issues are resolved.











Comments

  1. fr5 February 2023 at 01:34

    Perhaps not easy to achieve: place the wind vane and as5600 assembly on an axis perpendicular to the axis of the sailboat just above the AS5600 housing with a counterweight if necessary below to cancel the list.
    Rather than a beautiful 3D print of the wind vane support mast, use 3 carbon tubes with spacers in cnc cut or 3D print

    ReplyDelete
    Replies
    1. fr5 February 2023 at 01:38

      Better explained: rotate the current axis by 90°

      Delete
    2. Damian6 February 2023 at 05:02

      good idea - a counter-weighted pivoting vane would be great and some carbon tubes would be lightweight / low drag

      Delete

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