Turntable questions...to index or not...

[ShadowNix]

Thanks, Randy... I will be away for business for the next couple of days....but when I get back, I will do some more research...

 

 Brian

[rrinker]

 If it's really rightup front, you probably can do it without an indexing system. Or you could make a cheap eyeball assister - a phototransistor (smaller and more precise than a photocell) on the bridge and a series of IR LEDs at each stall track. Rotary switch selects which track you want (turns on that track's IR LED). Drive the bridge around until the phototransistor lines up and the LED comes on. Slightly more fancy is a comparator circuit that controls 3 LEDs - one for perfectly aligned and one to either side of a different color that indicates close but not quite. ANd the next step links that circuit with the track power to the bridge, so the loco can;t move unless you are lined up.


                                         --Randy

Randy,

I love your idea... a few questions I have...

1.  I presume an IR phototransistor will work well in the light or dark, but I just want to check ...

2.  I like the idea of having the power off UNLESS they are aligned.... (especially since I have little boys that will be driving trains in a few years....)

3.  Would you know of any basic circuit designs for this... of course, I can probably (big probably) design one myself, but I am much better at analyzing/building than designing... any circuit sketches for this would be appreciated.... 

Thanks for the input, all of you. 

Brian

1. Yeah, that's why I said IR, you can tune the circuit so normal room lighting won't activate it, yet it will still work if you turn out the lights for night operation.

2. Yeah, falling intot he pit would be bad... (there's a good picture of the real thing in the Digitrax Big Book of DCC)

3. I need to find some of my old stuff, I think the magazines ar elogn gone though (not railroad mags, electronic mags). One had a circuit that cold be adapted I think, it had the 3 LED thign I mentioned. The real purpose was to transmit voice over a light beam, the the LEDs were used to align the transmitter and receiver. It was in an old Popular Electronics in the early 80's, one of Forest Mims' designs, the guy was awesome. It was highly resistant to ambient light because the transmitting beam was modulated - and the receiver tuned to the same frequency. The other place to poke around is Rob Paisley's site, probably find something useable there.

                                     --Randy

[rrinker]

UKGUY, like your avitar. I agree, offered to let Randy use our guest house if he would help with mine. His posts have saved me more than once.

 One of these days I'll have to take you up on that. I need a vacation.

                                     --Randy

[ShadowNix]

 If it's really rightup front, you probably can do it without an indexing system. Or you could make a cheap eyeball assister - a phototransistor (smaller and more precise than a photocell) on the bridge and a series of IR LEDs at each stall track. Rotary switch selects which track you want (turns on that track's IR LED). Drive the bridge around until the phototransistor lines up and the LED comes on. Slightly more fancy is a comparator circuit that controls 3 LEDs - one for perfectly aligned and one to either side of a different color that indicates close but not quite. ANd the next step links that circuit with the track power to the bridge, so the loco can;t move unless you are lined up.


                                         --Randy

Randy,

I love your idea... a few questions I have...

1.  I presume an IR phototransistor will work well in the light or dark, but I just want to check ...

2.  I like the idea of having the power off UNLESS they are aligned.... (especially since I have little boys that will be driving trains in a few years....)

3.  Would you know of any basic circuit designs for this... of course, I can probably (big probably) design one myself, but I am much better at analyzing/building than designing... any circuit sketches for this would be appreciated.... 

Thanks for the input, all of you. 

Brian

[reklein]

I have built a Diamond Scale turntable complete with indexing system. While a little complicated initially once I understood what was going on I got it to working quite well. DS uses a system of contacts which work very positively in either direction.They also have a way to slow the turntable as it approaches the stop you need and a jogging button to position the track if needed. This is a nice system and is fairly idiot proof,aas it is on the club layout and is still operating reliably after a couple years.

I installed another system using a dtector which "sees" a white line on a tab projecting from a wheel mounted under the turntable. I'm certainly not an expert in installing this type of system and it showed. I had a lot of trouble trying to get the thing to stop correctly. There can be no backlash whatsoever in the turning mechanism as we had a lot of trouble getting it to stop in the right place and then the problem was compounded by the fact that when one reversed it the stops would all be 1/4" off. I spent about 3 days under the table whithout ever really reaching positive results, The best we could do was to rotate the table one way to get anywhere near the stops then jog it into place.

On my own layout I started with a slow motor but had trouble getting the thing to stop accurately. I considered hooking the motor up to my DCC system which prolly wouda worked but wound up installing a hand crank using the mechanism from an old oscillating fan and aligning by whats left of my 62 yr. old vision.

[claycts]

UKGUY, like your avitar. I agree, offered to let Randy use our guest house if he would help with mine. His posts have saved me more than once.

[ukguy]

After reading Randy's VERY knowledgeable posts for quite some time now I have come to the conclusion I would like him to wire my layout (I have no clue with circuitry and very little will to learn it), its all just too much to start at.... maybe I'll just end up running this TYCO 'Clementine' set I aquired around on the floor somewhere while I play with scenery and structures, and modeling and stuff....

Hmmm maybe DCC would be easy to learn... if I had the time....

In response to the question (with obviously no technical knowledge to back it up) I would say definately indexing of some sort... however simple it maybe.

Have fun & be safe
Karl.

[rrinker]

 If it's really rightup front, you probably can do it without an indexing system. Or you could make a cheap eyeball assister - a phototransistor (smaller and more precise than a photocell) on the bridge and a series of IR LEDs at each stall track. Rotary switch selects which track you want (turns on that track's IR LED). Drive the bridge around until the phototransistor lines up and the LED comes on. Slightly more fancy is a comparator circuit that controls 3 LEDs - one for perfectly aligned and one to either side of a different color that indicates close but not quite. ANd the next step links that circuit with the track power to the bridge, so the loco can;t move unless you are lined up.


                                         --Randy

[jwar]

Brian...Just a thought of how prototype turntable operated. The "hosler" operated the engines within the service facility, a hosler helper motioned him when to move the unit onto the turntable, and where to stop it. The helper would unlock the rail clamp and move the table to an ajacent track. If he didnt stop the table at the exact spot, he would jostle the table to align the tracks and lock the rail clamps. Sometimes an inexperienced helper would jog the table back and forth several times getting it in alignment., resulting in the units rocking side to side a bit.

We use to take bets (for coffee) on certain helpers, as to how many times they had to jog it, other helpers were so good they seldom missed, and if he did someone would yell "You Rookie" to razz him a bit..

To anser your question on indexing, if you can see the table up close and like to keep things simple, so what if you have to reposition it if you overrun the track a bit. Just a thought....John  

[TomDiehl]

Sorry, Tom, great question. HO scale.... Yes, I am thinking indexing is best as well, but looking for a relatively simple system...

Brian

The simplest I've seen, also includes the drive for the turntable, as long as you don't have a problem with the stepping motion. It uses the indexing feature of the Atlas turntable. You extend a brass tube down from your turntable and solder a small plate to it, small enough to sit on the Atlas turntable top plate. At this point, feed wires down from your turntable bridge track and solder it to the rails on the Atlas turntable. Epoxy the brass plate to the top of the Atlas turntable, being careful to center the tube over the center of the Atlas table. This way you've wire the turntable's bridge rails to the terminals on the Atlas one, taking advantage of their wiper assembly to feed them. Even if you rotate the same direction all the time, you're not twisting off the wires. Wire the Atlas turntable motor to 12 VDC through a forward-reverse (center off) switch, and you can turn either direction.

Probably the best example of the K.I.S.S. principle.

[ShadowNix]

Sorry, Tom, great question. HO scale.... Yes, I am thinking indexing is best as well, but looking for a relatively simple system...

Brian

[TomDiehl]

To index or not, yes index.

What scale are you working in? The smaller the scale the more critical it becomes, and more difficult to do by eye.

[ShadowNix]

Hey all,

I am planning to make a turntable from MDF (see below link) using this guys method (which I think is great, btw)

http://users2.ev1.net/~pvanvliet/Structures/Turntable/index.htm ) 

I will use his method to cut out the perfect circle, and I plan on laying hand ties and using a diamond scale dolly trucks

http://www.diamond-scale.com/Images/pg%206-Large%20Dolly.jpg

 as well as their arch

http://www.diamond-scale.com/Images/pg%206-Angle%20Arch.jpg

  Anyway, I have a 2 rpm motor I plan to control with a variable resistor setup.

My question to you all is regarding indexing.  I was planning to "eye-ball it" since it is on the front of my layout.  My question is, have many of you build a scratchbuild indexing system using photo-diodes or photocells?  I have looked up lots on the net, and while there are some quite complex systems, I am more of a middle of the road electronics guy... I am looking for simple (although I do make my own circuit boards, etc., so I could do a bit more complex, but I dunno).  Anyways, I wanted your all thoughts on this, since you guys have great ideas... Thanks for any help.

 

Brian

P.S.  I will be out of town for 2 days starting tomorrow, so sorry for slow replies...