We have a very special event planned for the next CNC Build Club meeting on Thursday, July 18th. We are going to do a Gonzo Build with the Make With Moto crew. Make With Moto is a Velcro covered Sprinter van filled with making equipment that is touring the country. In addition to the making equipment they have a bunch of unlocked and hacked Android smartphones. They have been doing hack-a-thons around the country.
We thought it would be awesome to do something that combines our CNC hacking skills with their phone hacking skills. We would temporarily remove the “a-thon” and do a one night Gonzo build.
The plan is to do a digitally controlled camera slider. The phone would replace the camera and control the motion. We are still seeing what is feasible on the phone control options, but ideally you could control the phone from a second phone and view live video or snap shots from the slider phone.
It will probably look similar to this camera slider that was done in the past, but it will have a mount for a camera and have all the drivers on the slider.
Inventables will be supplying all the CNC materials. As the details get more firmed up, I will edit this post so check back later. If you have any other ideas, let me (Bart) know. We may be able to get materials for multiple versions.
The project was to build a “single axis” drawing machine in one night. This machine uses two independently controlled carriages on a single piece of MakerSlide rail to control a pen at the tip of two linkages. The primary purpose of the project was a fun group build and a learning exercise in setting up a non-Cartesian machine using inverse kinematics. Kinematics in this case means mathematically describing the machine to the CAM controller. The One Axis DrawBot is a very simple non Cartesian machine.
The equations used are shown above. The ends of the linkages on the carriages end are at joint and joint. The pen is at pos->tran.x and pos->tran.y. The first two equations convert the desired pen location back to actual machine locations. They were plugged into the CAM program. The last two equations do the opposite and convert machine locations to the pen location.
We had one team assemble the machine, one team wire the electronics and one team setup the controller. It took about two hours to complete that phase. We try to use newbies wherever possible, so adding solder training into the mix usually adds a little time. The next step was to setup the CAM controller.
We borrowed the CNC router computer and control box to run the machine. This has Mach3 CAM controller software on it. Mach3 has a “formulas” feature that we used to enter the kinematics. We quickly had the machine running, but it was soon clear that Mach3 was not completely up to the task. In the formulas mode, it appears to disable the DROs (digital read outs) which tell you exactly where the machine is. It was also difficult to home or tell the machine the current location. Moves in the Y axis are non linear and need to know the current location. This resulted in Y axis moves that were not 100% accurate.
The other problem was coordination. If you tell a CNC machine to move from X0, Y0 to X1, Y0, it accelerates up to the desired speed then decelerates to the end point. If you tell it to move from X0,Y0 to X1 Y10, the two axes are moving different distances, so it needs to coordinate the different axes speeds and accelerations. The X axis would move quite a bit slower to coordinate with the longer Y distance to get a straight line. Mach3 was coordinating the two machine axes, but it was not coordinating the pen axes. Moves in only X or only in Y were nice and straight, but moves in both X and Y had a bit of a curve to them, but they did accurately arrive at the end point. A graphic with a lot of short moves would not show any on the problems above so we ran a quick “PS:One” graphic. Watch the video and be sure to wait for the applause.
We will switch to using EMC2 (LinuxCNC). This has a true inverse kinematics feature that should fix the problems.
There is some discussion on the EMC user mail list to help us with this project.
Update 6/23/2013: Here is the latest (untested) version of our LinuxCNC kinematics file mykins.c
This week the CNC Build Club is going to attempt Gonzo Build #2. A gonzo build is where we try to knock out a complete CNC project in one night. Gonzo build #1 was the Quantum Delta 3D printer.
Quantum Delta 3D printer
This week we are going to build a one axis 2D drawing machine. This uses two independently controlled carriages on the same axis to get 2D motion at the ends of the linkages. The purpose is only to have a little fun and to cut our teeth on a simple inverse kinematics machine before moving onto a much more complex 6 axis machine.
If you want to help, please join us. The meeting is open to non members. Please RSVP via meetup.
There is no special topic or speaker for this week’s meeting, but here are a few things we will be doing.
Member Certifications: Colin, Steve and I can certify on various pieces of CNC equipment including the Laser Cutter, Vinyl Cutter, 3D printers and CNC Router.
ABS Smoothing: Donald J is hopefully going to bring in his acetone vapor chamber for ABS print smoothing. Bring your ABS parts and a any spare fire extinguishers you have.
DSP Stepper driver tuning. I now have a programming cable for the drivers. We play with and learn about the benefits of stepper driver tuning.
Another group, gonzo CNC build? It might be fun to plan another gonzo build. We could kick around some ideas to try to build in one night again. I think a simple inverse kinematic (oxymoron?) project might be fun. Eventually I want to do a six axis machine, but it might be good to get our feet wet with a non Cartesian 2 axis draw bot. If you have other ideas, please suggest them.
I can bring in a few sample of V carving. We might do that the following week.