Stiffness of Fast Track crossover points / servo mechanism redesign

[bbussey]

Now that after two years I've confirmed the basement flooding issues are resolved, I've finally been able to make some forward progress on my layout.  I was able to test my servo mechanism on one of the double crossovers, and the points are too stiff for the .032" steel wire to move.  Any suggestions on how to make the points move more freely so that my mechanism will throw the points?

[jdcolombo]

Hinge the points?

If you look at the Fast Tracks video for their 3-way, you'll see their technique for hinged points.  If you've already hinged the points, then I'm stumped.

Just as an FYI, got no problems with a tortoise moving the points on a #4 turnout withou hinged points using .032 wire.

John C.

[robert3985]

I use a bigger wire to move all of my hand built turnouts with my Tortoises.  I used to grind the ends on my bigger wire so they were about the same diameter as the much smaller packaged actuating wire, but nowadays I use a small brass tube and solder pieces of the actuating wire that comes in the box onto the ends.  Works well for me and I can modify the "springiness" of the wire that goes into my throwbars by fiddling with its length.  Of course, ya gotta drill out the movable fulcrum to fit whatever thicker wire or tube you use.

[SkipGear]

Bryan,

 Is the problem the servo stalling or are the wires flexing too much?

 If it is stalling the servo, the next question is the controller limiting the output current or is the servo just not strong enough? Those cheapy micro servos from china have some pretty weak specs. Do you have the torque specs for the servo and what voltage are you driving it with? Since this is a special situation, a little more spent on a better servo may solve the issue.

[bbussey]

John — no the points are not hinged.  They are long though, as these are #8 double crossovers.

Tony,
The wires are flexing.  And it's pretty strong wire, I thought.  The points are stiff but not overly so.  Servo is working fine in the current scenario.  I guess I could "stiffen" the wire by putting a steel or aluminum sleeve around it and see if that helps.

[DKS]

If the machine is separated from the switches by a substantial amount (i.e., trying to actuate them through 2+ inches of foam), consider carving out an opening for the machine so that it is physically closer to the track.

[Chris333]

If the throw bars are moving freely I would look into shortening the distance as well. Those wires are moving pretty far, but the further out they reach the less torque they have. (I think  )
This is why my linkages use a very short arm to transfer all the power. I have used them through up to 6" of foam. I have never thought about how to power them.]
http://www.trainboard.com/railimages/showphoto.php/photo/10371/title/mr-scan/cat/500

I sometimes cut through the base of the points at the last solder joint, but really I have no idea if that would weaken them and cause it to fail. And my turnouts are shorter.

[bbussey]

The distance between the pivot point on the mechanism and the throw bar is about 1½", which I don't think is much.  I'm going to try the sleeves next and see if that makes a difference.  I have to order some steel tubing.

I really don't want to hinge the joints, as these crossovers are on the mainline and will see heavy freight and passenger activity.

[DKS]

I think I'd still try to reduce the distance between track and switch machine. I've used the tubing trick to stiffen the wire, and a lot of times what happens is the wire just bends more where there is no tubing. But I suppose it's worth a try.

[jdcolombo]

The distance between the pivot point on the mechanism and the throw bar is about 1½", which I don't think is much.  I'm going to try the sleeves next and see if that makes a difference.  I have to order some steel tubing.

I really don't want to hinge the joints, as these crossovers are on the mainline and will see heavy freight and passenger activity.

Well, 1 1/2" may not sound like much, but as others have noted, as the actuation point gets longer, the wire bends more and has less force at the actuation point.  My #4's are being actuated through 1/2" of plywood; the wire that comes with the Tortoise (is it .025 or .020?  I don't remember) wouldn't get it done, but the .032 music wire is fine (in fact, it might be a bit TOO stiff for this particular application).  But I could easily see that if I added another 1" to the actuation length, even the .032 wire might flex too much to move the points reliably (though with a #8, you'd think the stiffness in the points would be a significant amount less than on my #4's).  Anyway, if you don't want to hinge (which given the application, I agree that hinging would not be welcome), I think you have two options: get the servo closer to the turnout throw bar, as others have suggested, or make your wire stiffer (e.g., the idea of using a sleeve, or you could do what Bob does and use thicker wire with the ends ground down enough to fit the holes in the servo and throw bar - I'd probably try the sleeve idea first, since that's probably easier to do than precisely grinding the ends of a thicker wire).

John C.

[Van Horne]

I have also run into this problem on my current shelf layout based on hollow core doors.  I started building Fast Tracks #6 turnouts with solid points which worked marvelously with Caboose Industries sprung ground throw.  When I tried to switch over to Blue Points, no way could I get them to throw.  As noted, the width of the throw bar limits the wire size that can be used.  The idea of using a piece of tubing over the wire is one that did not occur to me, but sounds feasible.  To my mind, hinging the points negates a lot of the benefits of the Fast Tracks turnouts.  Anyway, I have reverted to using Atlas #7s for now.  I will save the Fast Tracks stuff for a future layout with a much thinner baseboard such as 1/2" plywood. 

[bbussey]

I have a ¼"-thick servo mechanism base + 1/8" plywood + 1" insulation foam board + 1/16" balsa wood + 1/8" cork between the pivot point and the throw bar, in that order.  I don't have the luxury of moving the pivot point closer to the throw bar.  I'm ordering some tubing online, so I'll know sometime this week if it works.  I have the luxury of the tubing length being from the bottom of the mechanism base to the bottom of the throw bar, leaving only 1/16" or so of exposed .032" wire that would fill the hole in the throw bar.  With little wire remaining to flex (the ¼" between the pivot point and bottom of the base), it should be eliminated as a failure point.  Then it will remain to be seen if the servo has enough torque to move two throw bars simultaneously.

I'll hinge the points as a last resort, which I can do by cutting the points rails in front of the copper tie and forming new point rails.  I can use Proto87 "joiners" since the points will be soldered to the throw bar, but that also means soldering the new point rails to the shortened frog to insure connectivity.  I was hoping to have some trackage permanently in place by the end of next weekend, but that looks doubtful now.

UPDATE:  I see Chris uses 1/16" brass tubing, K&S I'm assuming.  I'll try that for the wire sleeves first.

[GaryHinshaw]

FWIW (not much) I have been using hinged points in all of my proto:87-based turnouts, including a crossover on a grade sandwiched between two curves.  I've been running very challenging trains through them - some with mid and rear-train helpers - and I've yet to have a derailment or other issue that I can attribute to the hinge.

I have tried to take great care to make sure that the points have almost no resistance to motion, and I've actually downsized the Tortoise wire from .025" to .019" to minimize stress on the point/throwbar joint, which is a much bigger point of failure than the hinge, IMHO (especially if they require so much force to actuate).  I wouldn't be so reluctant to try hinged points.

-gfh

[bbussey]

Gary, I might end up traveling that route.  Thanks.

[Chris333]

FWIW If I only have to go through like 1/2" I will use something like this:
https://picasaweb.google.com/ErieChris333/HarlemStation#5645284500946825330
No pivots just a wire sticking up into the throw-bar.