While I’m still a firm supporter of the tried-and-true industrial foam tape method we’ve sold for MRServo servo switch machine mounting since the beginning, there’s always room for improvement. Several customers have asked about alternate, mechanical mounting methods, and there’s definitely places that would be useful. I always have a machine or two that keeps getting knocked loose as I accidentally catch the wire with a tool, or sometimes a spot on the plywood that just refuses to adhere well.
The “conventional” solution would be to have injection molds made, and then have a run of several hundred or thousand parts produced. This is obviously expensive for us, highly speculative that somebody will actually buy them, and beyond what the meager profit margins on servo switch machines justify. Fortunately, we live in an absolutely amazing time in terms of manufacturing processes, and nothing is more exciting right now for manufacturing complex plastic parts than 3D printing.
3D Printing to the Rescue!
I started messing around with fused deposition model 3D printing about four years ago, understanding the promise it held for being able to make customized or low production run parts cheaply. Basically, the technology lets me take a relatively low-cost spool of ABS plastic, melt it down into a tiny filament, and deposit it into incredibly complex shapes. It’s nowhere near as fast or as cheap (per unit) as mass production injection molding, but it’s fantastic at producing small runs of plastic parts without the up-front investment of mold making or needing to run a batch of 1000 parts at a time.
Unfortunately, I’ve been described in the past as “CAD challenged”, which I believe is a nice way for my mechanical engineer friends to tell me I should never be allowed to produce mechanical drawings of anything. This is where a a friend and coworker of mine, Mat Oransky, enters the picture. Mat’s not a modeler himself, but is the designated “electrical guy” for a layout up north. He’s also a rather remarkable and talented designer. As part of a discussion about other mounting brackets for semaphore drivers, I realized I should just ask Mat to create a few designs for MRServo as well. After bribing him with my old home-built 3D printer and working through a few iterations over the course of a week, we now have MRServo mounting brackets.
Brackets for a Variety of Applications
We’ve come up with three types of brackets. One will hold a MRServo-2 or MRServo-3 (since the boards are the same size), one will hold a MRServo-1, and one will just hold the servo with no control board. The first two have obvious uses, while the third is great if you’re using an extra servo as part of our “crossover kit” or if you don’t have room to mount the control electronics with the servo.
To install one, attach the servo to two large mounting lugs using the screws included in the package. The control board then just snaps into some mounting tabs. (Because the tabs themselves aren’t terribly flexible, it’s advised to just flex the whole bracket a bit to get the board to slide in place.) Once everything is connected, attach the throw wire and servo horn as described in the MRServo instructions.
Once the module is assembled, center the throw wire and run it up through your benchwork and the turnout throw bar. I highly recommend pre-drilling the holes to make mounting more precise, so while holding the machine in place, mark the two or three spots where screws should go with a marker. Remove the machine, drill some pilot holes and then mount everything using #8 1/2″ lath screws, available at most home improvement stores. The oval screw holes will allow you to adjust the machine back and forth slightly so you get good centering on the throw.
Open Hardware, As Always…
As with all of our designs, we try to be as open as possible. That means we’ll post all our design files, and you’re welcome to make your own or improve on ours in any way you see fit. Our only requirement is that we ask you share any improvements you make back to the community.
All three brackets are posted in the Iowa Scaled Engineering Thingiverse account. Not only is the STL file available (the thing you actually need to print the brackets yourself), but we’ve made the Fusion 360 source file available as well if you’d like to modify the design.
As a note, the STLs are for a dimensionally-correct bracket. That means you’re responsible for accounting for material shrinkage for whatever type of plastic you’re using to print it. ABS typically shrinks 2-3%, so I recommend scaling the STL up by 2.5% when you print it to account for that. Otherwise, the fit will be a bit tight. PLA, Nylon, PETG, etc. will all have differing expansion coefficients.
The brackets are not yet available for purchase, but will be within the next few weeks. We’ll also probably run a promotion for a day or two that any MRServo order includes free brackets, so keep an eye on the website if you want to get free stuff to try out.