I recently went to see my cousin in Michigan, who is a retired electronics engineer. I asked him about the possibility of making a turntable control that could be programed to stop precicely at any chosen position. Very intrigued by the idea, he's been working on it, designing the circuitry and the programming aspect of it.
As of now, I have to align the turntable visually, and it is difficult and my eyes are not getting better.
The question came up, would there be a market for something like this? it's going to use a stepper motor and digital control. If all works as planned, the indexing would be made programable to fit the spacing on existing roundhouses, not making roundhouse spacing fit the indexing.
Is there already anything like this out there, or is this something that could fill a niche? Your thoughts please? Dan
Ah. After posting the foregoing, a search reveals that Walthers makes a 130 ft TT with programmable indexing.
How well does it work? anyone here have one? Dan
Southgate 2Is there already anything like this out there, or is this something that could fill a niche? Your thoughts please?
I've been using a New York Railway Supply stepper motor indexing system for quite a few years.
NYRS Turntable Indexer by Edmund, on Flickr
It performed very well within its design limits. In my case, with a 130 foot Diamond Scale bridge there was just a bit too much back lash, or free play in the alignment to the radial tracks so you still had to tweak the alignment.
Turntable Stepper Motor by Edmund, on Flickr
The disk and microswitch (cam) is for my polarity reversal system but there is also a built-in polarity device on the NYRS controller.
I got to the point where I wanted better alignment control so I designed my own manual drive with a zero-backlash gearbos and reduction system using timing pulleys.
Turntable_drivetrain by Edmund, on Flickr
Turntable handwheel by Edmund, on Flickr
I like the feel of the positive drive using the wheel. I simply use a machinist's inspection mirror to hold over the bridge alignment to be sure I'm in good shape. There is no movement of the bridge through the gearbox and center pivot.
Cheers, Ed
Southgate 2After posting the foregoing, a search reveals that Walthers makes a 130 ft TT with programmable indexing.
the walthers TT uses a DC motor with a gear driving the TT along the periphery of the TT (not the shaft) and an encoder attached to the motor shaft.
the encoder generates a pair of pulses that count fractions of a shaft rotation allowing software to rotate the motor a precise # of fractions of turns. two pulses, one offset from the other allow direction to be determined.
i added an encoder to an older Walthers TT to index position and used a PID algorithm to drive it
when i lookde at using a stepper motor for controlling a turntable i found that a typical 200 step (1.8 deg/step) motor needs to be substantially geared down (1878 step for 130' TT) in order to locate the bridge at least within a fraction of a rail thickness. Ed's belts are one approach
another low tech approach uses a circular plate under the bench that can be driven with a small rubbery wheel on a DC motor. indexing was don by hanging small cardboard or metal tags ~1/2 wide from the plate and having a opto-detector that they passed thru. the tags can be "nugged" a little to align the TT
greg - Philadelphia & Reading / Reading
I have the Walthers, built-up, 90' with DCC indexing and it works great. Avoid the kit form.
I read that there were many versions of the 120' TT. Some earlier versions are to be avoided.
Simon
I bought the original Walthers Cornerstone 130' turntable back in 2005. The indexing feature worked quite well with one peculiarity. It overshot the programmed position, stopped, then returned to the correct position. That was the intended operation of the indexing feature according to the owner's manual. For the most part that proved to be accurate but not always. With enough fine tuning, the positioning could eventually be 100% accurate.
I eventually turned to operating the turntable manually. That proved to be faster because, once programmed, the turntable stopped momentarily at every programmed position. That took some time and the operator had to continue to operate the control box until the desired position was finally reached.
I believe that the subsequent versions of the turntable operate in a similar manner.
Rich
Alton Junction
I have the 110' Walthers turntable and it works flawlessly. While it does occasionally overshoot and then return to the intended position, the infrequency at which it does this (and the fact that it always lands on the right spot) tells me it may be somewhat intentional. Perhaps trying to look like an actual human is aligning it and "missing" once in a while. As for stopping at each programmed position, mine has never done this. Perhaps it was a program quirk from the earlier versions? I bough mine somewhere around 2016. Either way, it is always faster to call up the destination you want and press go than to try to do it manually. I wouldn't trade it for a manually operated one.
Mike
Water Level Route As for stopping at each programmed position, mine has never done this. Perhaps it was a program quirk from the earlier versions? I bough mine somewhere around 2016. Either way, it is always faster to call up the destination you want and press go than to try to do it manually.
As for stopping at each programmed position, mine has never done this. Perhaps it was a program quirk from the earlier versions? I bough mine somewhere around 2016. Either way, it is always faster to call up the destination you want and press go than to try to do it manually.
Didn't RR Mel use infrared to index his turntable? Whoa I actural found it on the first search. IR turntable indexing
Henry
COB Potomac & Northern
Shenandoah Valley