New 300 Series SubDriver Linear Servo Endcaps - input requested

[RCSubGuy]

As I'd posted up in another thread, one of the drawbacks to the rack and pinion linear servo setup in our new cylinders is the limited throw that it supplies (about 5mm). This can be overcome with proper setup of your control horns and other linkage connections, but it would be more ideal to have additional throw to play with.

I recall years (and years) ago, seeing something that used a wheel with steel cables to push and pull a linkage rod. This is a bit labor-intensive to produce, but the advantage is perfect linear motion with a high degree of flexibility in terms of alignment.

A couple of iterations and I came up with the following:




This simply press-fits onto a standard servo and provides over 12mm of travel end-to-end. I'm going to tweak this a bit for fitment and then I think this will be the new servo endcaps on our SubDrivers. Unfortunately, the outputs are not the same as the previous endcaps, so if you wanted to upgrade to the new version, you'd either need a new endcap assembly, or you'd need to fill the old holes and drill new ones for the linkage seals.


Bob

[Bob Gato]

I think that's pretty cool-I'll bet its quite smooth also- BG

[Scott T]

Stepper motors in old computer floppy drives had something similar. It was a metallic band shaped like a tuning fork.
Use to assemble them. Very precise. You might find this in an unused floppy or hard disk drive.

[Slats]

Hi Bob
that's a lot of re-working.
Can I humbly suggest that a cheaper method - how I set up all my boats is to simply employ an Intermediate Control Horn Pivot point external to the WTC.
I.e.

[Bob Gato]

FWIW those intermediate control horns just turned true linear back into parabolic and reversed the throws the added arcs further reduce the output throw distances which, as stated can be made longer by adjusting the distances from center pivot BUT reduces the mechanical advantage ...non linear is probably not a factor since it all happens aft of the the cup seals but the mechanical advantage might come into play.

[RCSubGuy]

Hi Bob
that's a lot of re-working.
Can I humbly suggest that a cheaper method - how I set up all my boats is to simply employ an Intermediate Control Horn Pivot point external to the WTC.
I.e.

Yes,

That is exactly what I envisioned people having to do, but it's not ideal. Some boats won't have the space to use this method, and some people won't have the skillset to properly implement it.

Reworking the endcap was simple enough, and the additional throw is definitely a good thing...


Bob

[Slats]

FWIW those intermediate control horns just turned true linear back into parabolic and reversed the throws the added arcs further reduce the output throw distances which, as stated can be made longer by adjusting the distances from center pivot BUT reduces the mechanical advantage ...non linear is probably not a factor since it all happens aft of the the cup seals but the mechanical advantage might come into play.

Hi Bob
yep that's exactly what is happening - however; to me, the linear advantage has much to do with minimizing any possible binding of the WTC pushrod seals that may occur if a swinging arm horn was used atop the servo, rather than losing mechanical advantage.

Noticed I used the words minimizing, may, and possible regarding binding of the WTC pushrod seals - as I have run subs since 1997 with both linear servo and swinging horns atop the servos and I didn't notice any binding / non-binding with either one. To me, Bob's offered me a linear product and I bought based on convenience as his end caps come designed for it. And in any case, I think the theory of having a true linear movement is likely to be kinder to pushrod seals in the WTC.

Regarding the mechanical advantage loss, I can't see how that's really relevant given the torque of the standard servos I use / and is readily used by others is massively over-engineered for the job that they do. Re the torque - I think that there is potential to wear and tear of your plane/rudder horns if you simply hook up a long push rod directly to the WTC. In fact, I have experienced that in some of my earlier boats back in the later 1990's, whereby the pushrods themselves had a slight sideways torque twist. I have built some 30 odd boats since then - with the intermediate pivot set ups and there is nothing to report other than smooth operation.

In the same way I run a small prop shaft through a stern bearing to hook up to an intermediate shaft that then connects to the WTC connection, an intermediate fixed pivot for your push rods ensures that your pushrods from their control horns on the planes and rudder are always operating within the same parameters.

Cheers

J

[RCSubGuy]

Another option for these units coming soon!

https://www.youtube.com/watch?v=tmHXAQSZNME