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Tiller Autopilot Limit Switches

The well known Raymarine (tm) ST1000 (and 2000?) series tiller auto pilot units have no limit switches built in risking self destruction.

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Tiller Auto pilot self destruction is a problem that has been reported on forums around the web for at least a decade. According to Raymarine these units are sound and well proven, the only known problem being that people tend to buy undersized units. This doesn't begin to explain why my unit blew up with less than a month of use on a light trimaran. Having zero patience for warranty services and the hassles of shipping my unit away for an unknown time period I opted to fix it myself.
The internet turned up several solutions which would be great for a one-off (not so quick) fix. Nowhere did I find a project that would be simple and easy for me and others to complete without a lot of filing and drilling etc. So I decided to design a 3D printed simple unit.

If you don't have a 3D printer that can do PETG or ABS, ASA etc you can go through a local printing service and order the 3D printed part for less than a hamburger meal at McD's.

Adding limit switches to the ST1000 and ST2000 is a great way of preventing serious damage to these otherwise wonderful units.

In my case the damage was already done. The motor had stripped the teeth of the toothed belt that drives the gears, and even stripped the teeth of one of the nylon gears themselves. Even the seal and outer bearing guide had been cracked on both sides. The files are hosted at printables for your convenience and mine (so I don't have to maintain my 3d printing projects in multiple places).

Adding these switches will prevent your unit from stripping off toothed belts etc

The 3D printable files are at Printables:
https://www.printables.com/model/570906-raymarine-st1000-tiller-autopilot-limit-switch-car

The 3D source drawings are at OnShape. Note that you only need access to this (free) if you want to edit your own version or access the 3D animated model:
https://cad.onshape.com/documents/ff892cc9957fb0d175a6a223/w/027790e8fd4758f3be9a786d/e/4644be35b096e6c55c23fbe9

(the OnShape document title is ST1000 LimitSwitches)


YouTube step by step walk-through for those who need it: (Sorry about the low quality video, I tried but no longer have the proper gear):

This hack was inspired by:

His video is much better quality and WAY MORE concise but his mod is technically more involved!

Another major source of inspiration for this was the following site:

https://www.cruisingonstrider.us/ST1000mods.htm

All source files and instructions are Open Source: GPLv2 or later.

Photos depicting a light grey / white printed unit are used with permission of the photographer Danny J. Mydlack who reserves all rights.

ActuatorRodFreedomUnits.pdf

This is a PDF of the stainless rod converted to US standard measurements.

Adobe Portable Document Format - 104.24 kB - 09/24/2023 at 17:51

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3dmodel01.png

A 3D render of the unit with stainless rod and switches

Portable Network Graphics (PNG) - 148.78 kB - 09/22/2023 at 17:31

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ActuatorRodDimensions.pdf

A PDF of the rod as a guide for bending

Adobe Portable Document Format - 96.12 kB - 09/22/2023 at 17:26

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LimitMicroSwitch.png

The dimensions of the micro switches I used

Portable Network Graphics (PNG) - 526.69 kB - 09/22/2023 at 17:26

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IMG_20230902_152142 (2).jpg

The original unit in position

JPEG Image - 3.45 MB - 09/22/2023 at 16:41

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  • 1 × AISI 316 Welding wire +/- 1.5mm or other stainless wire of a similar thickness This is to connect the inboard limit switch (max extension limiter) to the carriage. You bend this to the specified shape (in the drawings)
  • 1 × 3D printed swich base unit This can be printed by a service or on any well tuned printer in a more heat resistant filament than PLA!
  • 1 × Microswitch (small model) with lever 125V 5A min rating. Or simply cut off the wheel from the other type.
  • 1 × Microswitch (small model) with medium long lever and wheel (shorter lever will probably work )
  • 2 × Schottky Diodes 30V 6A or higher rated. Type 80SQ05 pictured The diodes I used are quite large and essentially overkill. These can get too clunky so be careful yours are not too bulky! Its also possible to substitute regular diodes, its unlikely that you would notice any difference in practice.

View all 13 components

  • 1
    Open the unit
    1. Disconnect from power and unscrew the screws on the bottom cover. 
    2. Carefully turn over and remove the top cover
    3. Remove the PCB (controller board) taking particular care not to damage the fragile connector coming from the flux-gate compass.
    4. Inspect and if needed replace any broken gears, belts etc
    5. The shaft output bearing / seal housing is available from printables.com (see next step) if you can't find an original part.
  • 2
    3D print the switch bearer main part or have it printed.

    Visit https://www.printables.com/model/570906-raymarine-st1000-tiller-autopilot-limit-switch-car/files
    and download the switch bracket .stl file. This can then be printed with 15% infill or higher recommended. 0.32mm layer height is fine but 0,2 looks better. For strength 4 layers of top / bottom and sides recommended. Skirt with tree supports touching build plate should be fine. It should fit snugly over the screw pillars in the base of the tiller auto pilot and lie flush with the top of the pillars when pressed into place. Note that the bottom edges of the pillar posts can be a bit ragged but that is purely cosmetic.

  • 3
    Insert the spring​

    Insert the spring into its 'garage' on the face of the switch carrier and make sure it doesn't fall out while you fix the micro switch to hold it in place.

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