Hi, (I'm a noob) I have 2 boring questions, sorry. I'm aiming to build a big plotter using the OpenBuilds ACRO Set. I see that the openbuilds software has plotter (pen) integration: My question: What kind of servo pen unit setup is best used for this ? Second question: Because of my location and the size of the plotter, I would have to order the vslots locally. The size’s here are slightly different, with the biggest difference being that they don't come with (V groove) edges. Here the profile: Will the OpenBuilds ACRO set work with this profile ? Cheers, Tim
You can come up with whatever will work for you, a few hours in CAD experimenting for example: Search for openbuilds | 3D Warehouse Here's on example (just add a way for the servo to lift it) Pen Holder V1.0 Lots of other inspiration :rc servo pen lift - Google Search (RC servos used to lift pens has been used for a long time, so many different ways to do it, depending on the tools and materials you have on hand (3d printable ones for example, need a 3D printer) Gravity pulls pen down toward the paper, servo arm just lifts up when you have to move between sections where it has to draw.
@Peter Van Der Walt Thanks for the tips, very handy! I'm thinking about using a solenoid (20 newton force). Unfortunately I need to print some parts, I will look something like this: (keeping it up at all times and down when the solenoid is activated) Hopefully it will be enough pressure on the bed/paper to draw. So here is where I lack confidence, it comes with 2 wires, can I just hook this up to the black box (controller box) ? Cheers, Tim
Should work, though if you can add some springiness to the pen as well. If the force "pulls" the pen down, its in a fixed plane, but the exam pad you are testing on may have height deviations. Pen gets caught up. Or if its a felt-tip, pressure ruins the tip. That's why I like using gravity (or maybe one rubber band at most) for downward pressure, and using the actuator (servo, solenoid, etc) to rather lift the pen up (as that can end in a fixed position)
I made a small prototype to get comfortable, and this brings me to ask some more noob questions. I'm using an Arduino Uno and CNC Shield for the controller: Since I've never done any of this, I don't know what is normal, and what is not. The motors make a slights humming sound when idle, they get warm over time but not hot. The heat sinks on the stepper drivers get burning hot, so hot it burns my finger. (slight smell of “hot electronics” becomes present over time as well, not a burn smell though) My motors (probably as a result of that) are acting weird: (video attached) They stutter or jump, I can't figure out what is causing it. I'm using: A4988 Stepper Motor Driver Modules. The current limit for my stepper motors is 1.7 A Motor Driver A4988 current limit = verf x 2.5 It reads 0.60 x 2.5 = 1.5a That's below the limit, so it should be good as far as I know. I'm powering the Shield with a 24V / 15a powers supply. And the Arduino n with usb cable from laptop. Another problem is probably software related. When I draw a 1mm diameter circle in openbuilds CAM, save and load it into the openbuilds Controller. My machine draws a 2 cm circle in realife. First I thought it might be some Inch vs MM problem but it seems more like a scale factor once it starts plotting. Again, I don't really know what causes it, or how to fix it. If anyone sees flaws in what I'm doing, please share those thoughts
Another dumb question. I managed to get a solenoid working when the dremel is activated. The idea is that I trigger a solenoid when the pen is up / or down. If I flash the machine style from: 2 axis to: 2 axis + RC servo. It doesn't get triggered on the servo pen up or down commands, actually nothing seems to trigger it after flashing. Does anyone here know how to do this?
So you can set the “servo” code to a custom number when creating the C-code. In my case I need M3 and M5, I can't do this in openbuilds CAM, there it will only let you choose M3 for some reason. Have to change it manually in the C-code itself. It works but when using Openbuilds Control it keeps giving me an error as soon as the “pen/solenoid” goes up. And then the whole operation stops..
It runs without errors if I unplug all limit switches. I also fixed the sizing issue by changing these numbers: It now draws in the correct size. My only problem is the heat and the motors, the longer the machine is on the more is stutters
I just blew my stepper motor drivers I think, sparks were flying while I was trying to take a measurement. ( now all of them are giving weird readings ) The CNC board seems to still work. I see other people power their CNC Shield with 12v instead of 24v, could this be the problem ? I thought powering the shield can be done between 12 and 36v?
Consider a OpenBuilds BlackBox: See https://docs.openbuilds.com/blackbox - protected drivers (; The "servo" firmware needs a S-value to move the servo - can't be abused for other purposes. If you need straight M3/M5 don't use the Servo build. Stock Grbl will turn the output on with M3S1000, off with M5 Or, Use a servo, much better than a solenoid: See docs:blackbox:connect-rc-servo [OpenBuilds Documentation]
Many months later I have a working plotter! However because of its large build volume 4m, x 1.8m, it's very hard to have the table to exactly the same height everywhere. This is easy to combat if I had a larger servo travel distance. @Peter Van Der Walt The Open-Builds software only allows me to “calibrate'' the servo about 30 degrees of rotation. Would it be possible to have the servo rotation go as far as 90 degrees?
You set the values, it can do 0-255 full 8bit range. The range should only be limited by your mechanics, or ordering the wrong servo (you get them in various ranges of what 0-255 does in real world, based on gearing in the servo. Full rotation, half rotation, and smaller increments too. Even continuous servos.
@Peter Van Der Walt I'm using a Using a Tower Pro 9g I've tried a Tower Pro MG995, but same results, only about 30 degrees of rotation Also tried a Tower Pro MG90S, but that doesn't seem to rotate at all. Is it because of the servos I use ?
Probably. Get some good ones from a RC shop, they'll have better specs of the torque and swing angle etc
I don't know what the problem is but something doesn't sound right. 30° is half the normal travel of a servo in on direction! Yours does it as in the total travel. These Tower Pro servos are normally quite good and worked for me with no problem. Both the metal gear and the plastic gear.
Thanks for the replies! @JustinTime I thought so too. I know I'm not supposed to power them from the Adriano, but the Tower Pro 9g only uses about 5v. I currently don't have a converter for separate power, so I take the 5v of the Arduino... Could this really be the problem ? It won’t do the rotation with the software as is.. But I did solve my problem by designing & printing a more efficient lifting mechanism. I now get more than a 1cm of lift with a 30 degree rotation. This is more than enough to level out uneven parts on the table top. If someone does know what the problem with the rotation might be, I would still love to know.
