The RAMPS is one of the oldest, but also one of the most flexible RepRap control boards – but is it still up to the job?
The RAMPS board
I’m Tom and today i’m going to review the evergreen RAMPS controller board setup.
Now, the RepRap Arduino Mega Pololu Shield really doesn’t do much on it’s own: It only provides an interface and carrier board from the controller’s brain, the Arduino Mega, the the Printer’s sensors, motor drivers and heaters. Because the RAMPS is essentially an adapter board, it can be used in many different configurations: It provides three high-power switching outputs of which all can be used for hotends or fans, and one of them can be used to drive heated bed. It also has five stepper driver sockets, and depending on how you configure your firmware, you can either use them for the X, Y and Z as well as up to two extruders, or dedicate one of the extruder sockets for a second Z or Y stepper driver. Speaking of which, you can use either the original Pololu driver, which, with good cooling, can supply up to 2 amps to the motors using the Allegro A4988 chip, or you can swap in the higher-power DRV8825-based drivers, which can supply a lot more current even without any extra cooling. Furthermore, the RAMPS has headers for all six possible endstops, three thermistor inputs, a dedicated header for hooking up RC servos, as well as five more expansion headers that expose about an extra 30 unused pins from the Arduino that you can use to add an SD card reader, an LCD screen, buttons, and you can also use them to control LED strips, fans and so on if you add a simple driver transistor for those. And if you know your way around the firmware, you can even use these expansion headers to add more motor drivers or heaters and for example expand the Ramps to basically as many extruders as you want. The only thing that’s limiting your imagination here is the memory of the Arduino. And while we’re at it, the Arudino Mega with its 16MHz 8-bit processor might not be as fast or modern as some of the newer boards that are derived from the 32-bit Arduino Due, but it still works just fine for almost every printer. The newer processors have other advantages, like being being able to run a web interface directly on the controller instead of requiring a separate Raspberry Pi.
Now, as the Ramps is one of the oldest and most popular boards, there isn’t just one vendor selling them. You can get them from China for about 20 dollars, but you will probably get them with sub-par components. This one is a review sample that E3D sent me, and it comes with all components as specified in the design files, which means that it’ll come with the proper transistors that can each handle the full 13 amps that a regular heated bed can draw, or even a bit more if you add a heatsink or some slight airflow. A good-quality RAMPS will also come with decent capacitors and copper thicknesses that can handle the current load from your heating elements. There’s also the option of assembling the board yourself, which means that you can choose the components you’ll be using. You can even make the printed circuit board yourself, but the whole effort of doing that is probably not worth the money saved.
But there are two severe design flaws in the Ramps design, no matter where you buy it from. The first one is these polyfuses. Now, there are two of them, one 5 amp one for the stepper drivers and extruder, and one 11 amp one for the heated bed. By the way, the Ramps has two completely independent supply rails, one from each polyfuse, which means that you can for example use 24V for the heated bed and 12V for the extruder and stepper drivers. But back to the polyfuses: These are bad design choice for a couple of reasons: 1) They are not rated for the current passing through them. The bed is fused with 11 amps, but regularly draws up to 13 or even a bit more. 2) These fuses are designed so that the power draw needs to drop below about half of their rated current to reset them when they have tripped. For the heated bed, this means that the fuse might go into a sort of undefined state where the heated bed still tries to draw power, but the fuse just doesn’t reset itself and then just acts as a heating resistor. Some polyfuses have burnt up from this, but if they don’t it’s going to be something that’s extremely hard to diagnose if you run into this behavior. I’ve personally spent almost a week trying to figure out what was going on with a printer that would apparently fail at random times. Turned out it was the polyfuses misbehaving. And last but not least, 3), the polyfuses rely on heat to trip them. I’ve seen some people use fans to cool the fuses and keep them from tripping, but even under normal use every now and then, a fuse might heat up enough to almost trip, which can cause some pretty unpredictable behavior.
Thankfully, these fuses are pretty easy to fix – just short them out and add some automotive fuses to the power input wiring. You can get fuses and fuse holders like these for a couple bucks at most automotive stores or even at radioshack as long as those guys are still in business.
Now, there’s one more flaw that all Ramps boards have in one way or another, and that’s the connectors used. Depending on where you’ll buy the Ramps, you’ll either get it with only screw connectors or screw connectors for the power outputs and a detachable one for the power input. Either way, these connectors are only rated for about 10 amps, so if you’re hooking up a normal heated bed, you might actually be overloading these and burn them up. And this is something that is not just hypothetical, but happening regularly. You can work around this by either soldering your supply and heated bed wiring directly to the back side of the Ramps, or by limiting the power output to the bed, but that will mean that you’re actually increasing heat-up times and limiting the temperature the bed will reach.
But all things considered, the Ramps is still a valid choice as a control board, and it’s also what I personally use for my main printer. Well, with a whole bunch of modifications, but the Ramps lets you easily do those if you want to. Even when considering that a Ramps from a reputable source costs around 40 dollars, and that you will still need to buy an Arduino Mega and at least four stepper drivers, the Ramps is still one of the most affordable RepRap electronics. If you can work around the issues with the polyfuses and the connectors, I’d absolutely recommend it.
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Here’s why you might want to skip those connectors: G+
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