FT/HSM motors with focusers of TS/WO/Chinese telescopes

The Optec QuickSync focuser motor series FT20/FT30/FT35 is sold Optec or branded by Starlight Instruments as the Handy Stepper Motor series HSM20/HSM30/HSM35, with minimal differences in housing looks. They are sold directly by both companies, or through several selected resellers/webshops.

The motors are mostly targeted at the FeatherTouch focusers of Starlight Instruments (SI), but also certain Astro-Physics and Takahashi refractors with adaptions.
I have used the HSMs with FeatherTouch focusers (FTF2008BCR and FTF2015BCR). Fantastic motors and focusers, fantastic combo. But then you get another OTA that perfectly fit your bill and needs, and because of design you can't even replace the focuser with a FeatherTouch.

A side note: FeatherTouch may be the absolutely best focusers in this league, but even a very few Chinese copies are actually getting quite close. This might become a dilemma when you are going to buy your next AP-refractor. No doubt, you can buy a Takahashi or a few others performing absolutely outstanding. But then you can buy a still quite good APO down to nearly fifth part of the price, even APO triplets with Ohara FPL-53 glass. Seeing isn't so great where I live. At an intermediate astrophotography experience level, that choice was quite easy. Further considering how much time I can spend on this hobby, and how many good nights we have, it became quite clear that I should put aside a considerable budget for well functioning gear, also takes the strain out of certain tedious operations like focusing, also making me not loose my interest in the hobby during all those -15°C nights.

My suspicion is (maybe I think too much) that the FT/HSM motors are not only made for, but also deliberately marketed for FeatherTouch focusers (almost) alone. I have been shopping from both Optec and SI. Jeff Dickerman and Wayne Schroeder (respectively) have been most helpful in discussing my needs, and I will keep returning for their various and slightly overlapping product catalogs.
But I don't think you should expect China-origin telescopes/focusers to become listed as supported in any of their web pages.

Firstly, let's look at the originals. Here's my Starlight FeatherTouch FTF2008BCR:

..with right focuser knob (the one with 1/10 reduction drive) removed:

..you need to measure accurately using a good gauge:

For the FeatherTouch FTF2008BCR and FTF2015BCR focusers, fitting the HSM20 and FT20 perfectly (made for them), my measures (mm) are 1) 25.40, 2) 10.80, 3) 6.47 and 4) 9.78. Also, the reduction pin diameter is 2.77mm, but that is said to not vary or be a problem.

The motor will grip the reduction pin. Meaning, your measures of 2) and 3) can be shorter than mine. Measures 2) plus 4) shouldn't me longer than the sum of my corresponding measures.
Measure 1) can't be bigger (25.40 in this case), but you can easily shim one millimeter or so if your measure is less.

For example, with the TSAPO71 (virtually the same as William Optics Star 71) and APO130f7-P, I came out 0.8mm short on the diameter. So I raised the radius 0.4mm by carefully adding four or five turns of 0.1mm alu-tape. This approach is no problem at all, since the motor tightening bolt will evenly contract the housing. (no bolt/setscrew that jams directly)
Note: The integral focusers of the two mentioned scopes needed the HSM30/FT30 for 32.9mm mounting diameter.

Here's the TSAPO71 with focuser knob/motor removed:

Back to adding a HSM20 to the FTF2008BCR:
..before we go, look at the cutout of the brass, meant to accommodate the parts of the focuser shaft: ..and done, secured by merely tightening two screws:

Quite similar, heres my TSAPO71 with HSM30:

..and and APO130f7-P with HSM30:

To be updated: There's a number of new (supposedly very good) budget OTAs around with a new type of integral focusers, like the TSAPO906. Mounting diameter (measure 1 above) is said to be 25mm, which is exactly what the HSM20 and FT20 models want. Haven't yet got anything on measures 2, 3 and 4. Waiting to hear back from Teleskop-Service.