Testing turnout linkages

[rrinker]

 I am planning to use RC servos as my turnout motors, using circuits from Tam Valley and Hans DeLoof to drive them. One interesting method of mouting them is pictured on the Tam Valley site, and initially appealed to me because this is how I mounted my Tortoise switch machines on my previous layout - attached to the bottom of the turnout wit a small piece of perf board. I simply cut a hole in the foam top and set the assembly in place. The linkage ran only the thickness of the roadbed, so there was no need to use heavier wire than what comes iwht the Tortoise, as this is even less ditance than if you used 1/2" plywood as the roadbed.

 I have a couple of scrap pieces of 2" foam so I decided to do some experimenting. Moving things by hand, it seemed that even through 4" of foam (I am using 2 layers of 2" foam plus a piece of 1/4" plywood for my base level benchwork) there was no problem with a long piece of music wire moving the points. So today I tried a more thorough experiment with the actual servo. Much like a 'typical' Tortoise install, I made an oval hole underneath the throwbar. I bent a piece of .032 msuci wire to fit in the servo horn, and attached the server to the bottom with double-sided tape. Control was via a Tam Valley Singlet. After adjusting the endpoints, it actually worked, although not reliably (I was using a micro servo, not the mini type supplied with the Singlet). I replaced the micro servo with the more powerful mini servo that came with the Singlet and now it was completely reliable. Keep in mind, servos are NOT stall devices, they need to move to their set point, not get held short. With the mini servo and the end points adjusted so the servo could reliably move into position, I found there was more then sufficient tension on the points to keep them in place. Pushing them to the opposite side and letting go caused them to snap securely back to the set point.

 My analysis of these results tells me that even with 4+ inched of distance between the actuator and the points I do not need extra-heavy wire. I would say this would also apply to using a Tortoise. This is for free-moving (hinged) points, not solid rail or those with a stiff spring (like Peco). For those you'd need heavier wire to get enough force, or remove the spring in the case of a Peco. My turnouts are Atlas Custom-Line Code 83 in HO.

                                                --Randy