Has anyone attempted to use a simple DC motor, Arm & Thread/wire as a Turnout machine? Kinda like this:
Of course this is very basic & would need a physical stop for travel control of the motor… but does anyone have any experience with this or something similar?
Although the linkage is different, that’s basically what a Tortoise is.
However, it’s important to note that the Tortoise uses a “stall motor” that draws only a very small amount of current once it’s “up against the stops.” This maintains a constant force to hold the points against the stock rails. If you just pull the points over and then remove power from the motor, there will no longer be anything to hold the points firmly, and they will vibrate off and probably cause a derailment.
A standard DC motor will draw more current when you stall it out like this, and will likely burn out after a short time.
The Torque Master, aka Switch Master, is what you are drawing, except the linkage can’t be done that way. Micro-Mark also has one called the Switch Tender that is very similar to your sketch.
What you call a “simple DC motor” won’t work, as has already been pointed out. The motor must be able to be stalled without overheating or drawing more current.
One of the small, battery operated motors like those found in a pager might work if it had enough torque, but the current draw and heat buildup when stalled would need to be determined. These types of motors can be purchased for as ltitle as $1.25 each from places like All Electronics.
Exactly what I am after… just with a pricetag lower than a tortoise 
I was also thinking about looking towards a rack & pinion set up on the motor. This would make it very hard to move the motor from the points, thus elminating (almost) the potential for the points to drift when the motor is de-energized.
Also, what one can do to prevent the motor from burning out is to put limit switches into the system that will shut the motor off when the turnout reaches the desired position. Additionally, if the turnout vibrates out of where its supposed to be, the limit switch drops out and the motor re-energizes, forcing the points back. My only concern is the tight tolerance on the limit switch calibration…
Has anyone used servos (as used in remote control vehicles) for this? I tried a search and came up with a couple of hits on servos but they were buried in pages-long posts so I couldn’t find the specific post that referenced them. Lightweight servos are pretty cheap.
M
The problem with servos as in RC cars or airplanes, is that they operate on a “pulse train”, and you would have to have separate source to power each servo.They can be operated without a radio on, with a “servo tester unit”, but each one would have to have it’s own controller, and would quickly get expensive.Plus the fact a servo motor with enough torque to operate switches could run anywhere from 25 to 45 dollars apiece, PLUS their control units.
Tortoise 's make this look cheap!
Your picture shows a method that probably won;t work as the torgue required would be too great for the motor to overcome. If you had a long enough shaft wrapping the cable around the shaft so you could pull the points in both directions would probably work better.
Good thinking. I was thinking about a simple gearmotor to up the torque and lower the speed.
How much torque does it take to throw a turnout? Lynxmotion has 57 oz./in. servos for $12.99 and the SSC-32 servo controller ($39.95) can control 32 servos. Slightly smaller servos are a bit cheaper. I have a walking robot that uses servos to move its legs (six legs with three servos each). Seems that should be enough to move the points?
Here’s the link:
http://www.lynxmotion.com/
I’ll have to try rigging up a servo to see if it’ll work - might not but can’t hurt to try.
M
[edit]Oh, and if you don’t need all 32 i/o lines you can use them to control signals, etc.[/edit]
Dave,
You are basically describing the switchmaster/Tortoise design. I use Switchmasters, and yes, they are expensive. Being the thrifty (some say cheap) modeler that I am, I bottom feed ebay for these. I have picked up used Switchmasters as low as $4.00 a piece. I’m sure that similar buys can be made on tortoises.
The motors and gearing in Switchmasters are made by a company called Hankscraft. The motor housing contains gearing to slow them down. Hankscraft sells many types of motors and gearing ratios. The main application is display animation (the beer bottle display that rotates etc). I have found Hankscraft motors on Ebay in the commercial display section with other gearing ratios which didn’t work for turnout applications. Lest you think of buying direct from Hankscraft (presuming they would sell direct), I think the minimum order is 100 units!!! Basically the Switchmaster company is buying these motors with the correct gearing (possibly specially made for them) and re-selling them with some hardware.
In addition to the other types mentioned already, Steve Hatch at Railway Engineering has a different design stall motor for sale.
Check his website for details: http://www.railwayeng.com/switch.htm
There are a couple of ways to install Switchmasters, the crank pin method (see photo) and the slot under the throw bar method, which is similar to the common Tortoise install. While I’m not crazy about the crank pin look between the ties, it is a very easy install (compared to measuring and cutting a slot) and can used in many awkward spots where the under layout geography is such that placing the machine directly under the turnout is not possible. Switchmasters are very smooth, last forever, are very quiet and do not slam the switch points like “crash and banger” solenoid style machines (Peco, Atlas, Kemtron
c1977:
Why not try building a screw-drive machine? You could use a regular machine screw, and tap a piece of brass bar for the nut.
Scale Shops sells a screw drive machine kit. In my opinion it is hard to slow down to a reasonable speed. But it’s pretty cheap and the parts are acceptable quality.
George
What I would like to know is why has nobody invented a machine that uses muscle wire? One moving part, no noise or vibration, slow action, simple interface, cheap.
George
They have. Many layouts in the late 40’s used choke cables from cars (back when cars had manual chokes). Simple and easy. They are still available with any length required. The only requirement is that the sheath be fastened at both ends to prevent it from moving with the cable.
Not sure but I think muscle wire might not have the strength to do it - I think it’s pretty weak stuff but I’ve never tried it out for anything so I’m not 100% on that.
M
Model Railroader had an article back in the '60s about using Nichrome wire (stuff used in toasters) to drive turnouts and crossing gates. A spring kept the wire stretched. The Nichrome wire would expand considerably when a current was applied and return to its original length when cooled. IIRC, a 10" length of wire driven by 12 volts provided enough expansion to let the spring throw the turnout.
Drawbacks were current draw and heat of multiple machines in the “on” position at the same time, air drafts cooling the wire prematurely, and assembling the frame for the spring and wire. But it was quiet and slow moving when only twin coil machines were available.
I imagine muscle wire would be much the same, with perhaps less current draw than the Nichrome wire to achieve the same result.
just my thoughts
Fred W
Been thinking about the whole rack & pinion or linear actuator style using a bolt & nut. As mentioned, the speed will be an issue, but using a fine thread pitch will slow down the travel speed.
Lots of good ideas all, thanks!
Way back when, I used Nichrome wire and it worked great except as was mentioned air flow would alter the wire. This was overcome by covering the hot wire (as it was refered to at that time) in a tube. Even summer and winter temps required ajustments. The good side was it was very cheap.
I also tried small DC motors with a threaded shaft. Worked fine but the noise was unbearable. I now use Tortious in unreachable spots and rods moving a overcenter spring arrangement. The turnouts very close to the edge are Peco and are digit thrown.