Improved Points motor with indicators by dagnall53

Last crawled date: 3 years ago

Sept 2019: I have published an "Improved Improved" design. (https://www.thingiverse.com/thing:3883510) this is a major redesign with the rack now mounted "under" the servo. I have also modified and simplified the indicator.
I will leave this Object here for reference or if you need to print spare parts. The indicator parts should be interchangeable with the new design, but all other parts have been modified or re-drawn.
Comments from earlier versions...
There been comments about the pinions and servo fit:
My three gears (s,m,l) are supposed to have holes (hex holes) 3.9, 4.4 and 4.8mm flat to flat.
I discovered that I had two types of ES08MAII servos. -- presumably one is fake? --.
One has 4.7mm pinion (and is 11.9mm thick) , the other 3.9 (and is 11.6 mm thick) .
My examples of ES08DE have plastic pinions of 3.8 and are11.7 thick.
I also use TGY9081MG , with 4.8mm pinions, which is 12.2 thick and a bit longer, but the pinion to flange dimensions are the same so they can be interchanged with the ES08's.
The pinions designs are not exact fits, just sizes I hacked to work with some of my servos.
I also recently had pinion fit issues with some new prints, but realised that the pinion "hex hole" was getting distorted at the first layer, squeezing inwards, making fitting difficult. This is a consequence of the first layer being wider than the others for adhesion purposes. A quick knife bevel around the hex hole sorts this ok.
Other - (Even older!) Notes:
My previous points motor used a slightly smaller drive to the rack, which required that the servo turn almost to its full extent to make the points switch. This sometimes made setting the unit up on the track difficult, as the drivers could not always get the required servo range.
To overcome this I have used a larger cog, so now the rack can be driven over a larger range, which makes setting the servo up easier.
When assembling, the servo should be centred, and the cog placed on the servo so that the vertical marks are vertical. This should give you roughly symmetric movement of the drive rack.
The new design is better matched to LGB dimensions, so the "servo centre" should now be roughly "points centred" regardless of how you fit the drive to the points.
I have also designed an illuminated snap action indicator to show the points direction.
This uses a small offset drive that is placed on the "opposite" end of the rack, which engages with a small circular driveshaft that holds the actual indicator.
There are indicator variants with Arrows or RhB markings that then fit into the drive.
For illumination, a 3mm filament bulb can be placed in the indicator (or a small LED).
The snap action of the indicator should snap as as the points go over-centre, but it may be that you need to offset the drive slightly, so I have made drive pins with 0.5 and 1 mm offsets that you can use to "tweak" the action. The drive was designed to use the smaller "pin" but sometimes I find that the larger pin makes the indicator snap better.
There are two versions of the drive shaft that the pin engages with. The first has a "full" 90 degree drive and this seems to work well with non illuminated indicators. But I found that with the wires from the 3mm filament lamp the indicator was "dragging" and only moved about 60 degrees. To overcome this, I have added a second version of the drive with 60 degree drive angles, that forces the indicator to move slightly further, giving the full 90 degree movement to the indicator.
I use 1.7 by 10mm self tapping screws to hold everything together.
The servo should be a ES08DE or ES08MA, which for me fits the "S pinion".
The "9G" servo is roughly the same size (it is actually 1mm "greater height " ) , and takes the "L Pinion".https://youtu.be/2D8CQbFnBPE
I have included the 123D file if you wish to adapt this, but only for non commercial purposes.
Thanks also to Marius (https://www.thingiverse.com/2009marius15/about) who suggested the two part illuminated indicators, and who made and tested some early versions to help sort out the design.