The world can delay me, but it can’t stop me. (huzzah)
I got some v2.1 opto end stops from the guys at Makerbot and a stepper plastruder from MakerGear. It actually didn’t take all that long to get them put together. It also didn’t take much time to start testing the printer and realize that it wasn’t doing what it was supposed to do. Then I got frustrated with programming (black magic) and then other things got in the way. Anyway, I got the programming problem solved and now have a Mendel that at least pretends to do everything it’s supposed to do. I’ll share any secret tuning tricks as I run across them.
BTW, what made my Mendel do stupid things was apparently having the end stops inverted in the firmware. If you get everything hooked up, and the end stop LED lights up when you break the beam, but your axes won’t move in both directions, try switching the inversion of the end stops in the firmware and re-uploading it to RAMPS. I guess the controller thought that on was off, or off was on, or something like that.
Before you do that, however, you’re going to have to get those end stops built and hooked up.
NOTE: There are some incidental parts and tools necessary to finish this build. I suggest reading through it first and figuring out if you need some random part like a single 2.54mm connector and its associate crimps. It can be pretty frustrating to realize you need to wait a week to get the right 0.05oz part.
- Get out your end stop PCB and take a look at it. Not too complicated, right?
- Go ahead and put all the components in place. I suggest just buying the kit, but if you want to track them all down individually that’s your prerogative. I didn’t use the RJ45 jack because that’s pretty old-skool (also it doesn’t work with RAMPS).
- Solder them so they don’t go anywhere. You might as well do all the boards at once. I got 6 so that I could have min and max end stops if everything went well, and if I broke any of them I could use the maxes as spares.
- Here are some other resources for opto end stops: Makerbot and RepRap.
- The best way to connect the end stops to RAMPS is to use servo cables. At least, it’s easier than building the cables from scratch using 2.54mm (.1″) hardware. You can do that, but it’s a pain. We’ll get to that later.
- Hopefully you thought that was all really easy…cuz now comes the hard part. The RAMPS board has two of the end stop connectors reversed; something about squeezing thicker traces on the board. This change means that you can’t just plug the end stops in to the board. First, you have to reverse the two appropriate wires in the connector. To do that you have to get something pointy into the back of the connector and pull up the tab that holds the crimped connector in place.
- Be gentle. You don’t want to damage the tab.
- Now you can switch the two wires. Which two wires, you ask? That’s a good question. As you can see on the PCB, there are three pins labeled VCC (+ voltage), SIG (signal) and GND (ground or – voltage). Basically, you’re going to want to switch the wires that are connected to SIG and GND. You can do it at either end of the cable, but try to keep it consistent so it’s easy to check your work. The connectors are labeled on the opto end stop board and on the RAMPS board, so check each a couple times.
- Do that for every end stop you’ve got. Then I suggest making a big loop of tape (sticky side out), and using it to line all your components up side-by-side for a final sanity check. If you bought a weird color of cable because it was on sale you might want to draw a chart or something to keep track of which colors are which.
- It might be at this point that you discover your cables aren’t long enough. Tough.
- No, but seriously, if that’s the case you’ll need an extension cable. One way to accomplish this feat is by grabbing a scrap rail of headers that are long enough to go into both female 2.54mm housings. The 90 degree headers are good for this.
- Just bend them and cut off chunks of 3.
- At this point things get hard to define. Mounting the end stops isn’t all that complicated, but you can run into weird interference issues. The more true to the Mendel build materials and process you stayed the less problem you should have. I used 6-32 socket cap screws instead of 3mm (USA! USA! USA!) because they were cheaper. They are almost 3mm, but they’re big enough that I had to drill out the end stop mounting holes. Then I realized that one or more of the end stops liked to wiggle around, so I had to create a tiny little brace to keep it immobilized. Just do whatever seems to work for you.
- I suggest using aluminum flashing for your opaque opto end stop triggers because it’s easy to twist into the weird shapes necessary. It’s cheap, abundant (can pick it up at any hardware store) and most importantly it’s a nice raw material to have around the shop. You can cut it with regular scissors and drill it, so no special tools required. Before you unroll it for the first time, take note of how it’s got that tape holding it together; you want to maintain that (it doesn’t like to roll back up again). Try to keep it from unrolling with one hand while you cut off a thin strip, then tape it back up again before it can pop loose.
- You’ll have to move the axes around to test fit the end stop triggers. X and Y are easy…Z not so much. You’ll have to get the axes working properly before you can figure out what shape to make the triggers for the Z-axis. I set mine so that the min end stop is triggered just AFTER the extruder touches the build surface. I figure it’s on springs for a reason.
- The MakerGear plastruder build is already documented pretty well over at Makergear.com. I got the 1.75mm version, and the associated PLA, because I wanted this Mendel to err on the side of accuracy. However, many of the parts in the plastruder are still sized for 3mm filament. Because of this I had a bit of trouble getting the 1.75mm filament to work correctly, but I have been assured that it’s supposed to work just fine. Make of that what you will.
- Pay particular attention to the steps that involve crimping connectors onto the ends of wires. It’s a delicate operation that is guaranteed to frustrate. Unless you’re already good at it or you have a special crimping tool (in which cases you’re probably only reading through this for a laugh). When you solder the crimp onto the wire be careful to keep the solder from wicking up in between the guides on the “top” of the crimp. If that happens, the crimp won’t go all the way into the connector and you’ll have to get that solder out of there (yes I did that and no it’s not fun).
- I suggest using different sex connectors on the thermistor and heater wires (one male and one female) that way you can’t get them mixed up in the future.
- When you’re all done building the plastruder you’ll probably discover that the motor Makergear supplies doesn’t have a connector on it, just loose wires. What you want to do is install a 1×4 2.54mm connector on the end of those wires, because that’s the spacing of the headers RAMPS uses for connections. I had one of those, and the appropriate crimps, left over in the RAMPS kit I got from Ultimachine.
- Install the crimps on the wires, then apply just enough solder to secure them. Take a look at the other motors on your Mendel to figure out what order to install the wires.
- Make sure the crimps are all oriented the right way (so the tab will catch them) and shove them into the connector. You might have to get creative with a pair of needlenose pliers to get them to lock in place. Keep in mind that there’s not much space in there, so if they’re not going in all the way you might want to mash the crimped part into a narrower profile. See how the crimped part of that red wire is kind of wide? Just squeeze that into shape. (don’t deform the part of the crimp that goes into the front of the connector…that would just break it)
- Now you can hook the plastruder up to the appropriate locations on the RAMPS board. The motor connector goes next to the extruder Pololu board, the thermistor goes on the T0 pins, and the heater wires go into the D9 terminals (or whichever ones show 12 volts when you try to turn on the heater). I suggest not bundling the thermistor wires with the heater or motor wires since that might cause noise in the temperature reading.
- Now enjoy the unique feeling of having all the mechanical and electrical work done because you’re looking forward to a long period of time messing with the software trying to get the machine to do what it’s supposed to do.
- I’ll put together another post on just that subject…whenever I conquer it myself.
- I like round numbers.