Point motors, re-invented
Well, I guess I ought to have known that I would end up doing this, so, yes, wheel re-invention was the order of the day.
Putting that to one side I think I have come up with something a little different, perhaps more flexible while being simpler to print and deploy (though that last point really will have to wait until I have actually installed one and got it working).
I have chosen to divide the whole "model railway point motor" thing into two distinct parts: The component which interfaces to the point itself, and the component which provides the driving force to actually move the point. So, following the picture painting a thousand words ethos:
The point interface:
and the Point Actuator:
I'll quickly point out that I realise that the the interface unit only catches the "bottom" switches, I have to extend the 3D model and raise the post up another 4mm.
How would they work (I can't say "how do they work", yet )? Hopefully it's obvious they screw up under the base board, where a suitable metal pin inserted into the post of the interface unit would engage with the point itself. The interface unit can be aligned and positioned such that it is centred lined up with the tie bar of the point. This interface unit (in deed both units) have a maximum 10mm swing which should be way more than required for normal usage.
The actuator unit clips onto either side of the interface unit and (with the servo motor in it's "zero" position, as per above photo) moved until the point is accordingly set. The 3D printed "springs" allow for both some freedom of alignment and also a little extension or compression hopefully making the whole arrangement easier to install and set up.
So how do you adjust the "throw"? Two ways: Firstly you could simply drive the servo through a limited arc rather than a full 180 degrees and 10mm of movement. Or, secondly, change the offset of the hub in the actuator wheel for one where the centre of rotation is closer to the centre of the wheel. At the moment I am thinking that a combination of the two is the best approach.
What I like about this design are the following:
- The servo is not actually attached to the component interfacing with the point, in the event that something needs doing to he servo there would be no need to fiddle with the point and risk upsetting something that can be tricky get right (not to mention a whole bunch of wires)
- There is no direct mechanical linkage between the servo and the point roding. To remove the servo simply unscrew it and drop it off its actuator rod. SImples.
Of course this is all, currently, hypothetical. I think I shall have to make up a small "plank" test bed to see just how this is actually going to work. The best laid plans and all that stuff.
The switches on the actuator will perform the normally anticipated "frog polarity" thing. "But wait", you say, "that only needs the one switch". Yes is the reply, however, the software I have been writing can accept confirmation signals (in the electrical sense) that the point movement has completed, and this is the purpose of the other two switches: they will pull down Arduino pins to earth allowing the software to know when a point is set (and which way) and also when it is "in motion" between states.
Anyway, some more images:
For info: CAD done using FreeCAD 0.18.4 exporting to STL and into Ultimaker Cura 4.4.1 under Linux Mint 20 Cinnamon.
Been trying to get these all "lined up" for a while now. Some of my issues were software related, but there's been a fair amount of mental re-alignment required as well
Jeff.
Edited by jeff_p
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