I am building a planar RR arm to be used for drawing. The arm will use two servos for joint control and be made of predominantly polycarbonate. At the end effector is a pen holder which will allow the robot to grasp a pen. The robot will create continuous line drawings based on images that are converted into path files. Below are some additional images of the arm design including my concept sketches.
Valentino Braitenberg is an Italian-Austrian neuroscientist. In his book, entitled “Vehicles: Experiments in Synthetic Psychology”, he performs thought experiments creating vehicles which, while simple in nature, exhibit complex behaviors such as fear, love, aggression and optimism. His vehicles are simple, with the simplest consisting of a single sensor and single motor. This simplicity makes it easy for someone to construct one of his vehicles. While Braitenberg like behaviors can be programmed into any robot with the proper sensors and actuators it is a more interesting challenge to construct a Braitenberg vehicle in hardware, as described in his thought experiments.
Due to the interesting nature of Braitenberg’s vehicles, the CMU Robotics Institute has provided funding to a project to create Braitenberg-esque vehicles that would then go on display in the Robotics Institute. I’m acting as co-project leader, coordinating with a graduate student in the Machine Learning program who obtained the funding for the project. I’m hoping the project will produce 5 to 6 artistic Braitenberg inspired creations. I’ve spent some time thinking about possible things I could create and I’m excited to see what ideas other people come up with after I present the project at the Robotics Club’s general body meeting.
More to come on Braitenberg in the coming weeks as projects get started.
I built a frame that paint bot can be mounted on for testing. I built it out of scrap lumber from the CMU Robotics Club. The frame has the motors mounted near the top with the cables running through guides at the top of the frame.
I currently do not have any sort of painting mechanism mounted to paint bot. I’m thinking about building a marker holder so I can test it a little easier than using spray paint. Currently I just have a weight attached to the two cables to simulate the painting mechanism.
I completed the main electronics board for Paint Bot in Mid-July. The control board consists of an Arduino Microcontroller, a motor driver from Pololu and a custom circuit board (perf board) that does some interfacing for the sensors. The board is mounted on a piece of 3mm acrylic.
I’ve been working on trying to learn more about stepper motors. In the past month or so I’ve learned that there are two varieties of stepper motor: Unipolar and bipolar (and sometimes both!). In all of the research I’ve been doing I came across a lot of great resources. They are listed at the end of this post.
All of my interest in stepper motors comes from the fact that the Robotics Club recently received a large supply of nice stepper motors and because the original spray painting graffiti bot, Hektor, as well as some other recent Hektor-esque bots, used stepper motors for its control. The particular motors that the Robotics Club obtained are 6-wire stepper motors. This means they can be used as either unipolar or bipolar steppers. This is very useful because it gives me a larger range of control options. However, the motors run at an odd voltage (3.68 volts) which limits the range of available drivers ( I’ve only found 2 capable of driving these motors). Due to the lack of available motor drivers for all these stepper motors we now have, I decided to build my own.
After doing some looking, I decided to control the motors in unipolar mode because the control circuit is simpler. The circuit I build, which is based on this one, is basically 4 Darlington transistors which are used to toggle the coils on and off and some diodes for protection. The stepper motor driver turns each one of the four half coils in the stepper motor on and off sequentially to drive it. The original circuit uses a L297 stepper motor driver to handle sending signals to the Darlingtons, but, I didn’t have any on hand, so I just sent the signals sequentially from and Arduino.
To test the circuit, I didn’t want to potentially harm one of the nice stepper motors we have, so I was using an old stepper motor out of an IBM floppy drive. I couldn’t find documentation so I couldn’t figure out what order to toggle the coils to properly step the motor. I was able to get it to step some, but never rotate continuously. It would step a bit one way, and then step back. I believe my control circuit was ok, because the motor was able to step some. The issue at this point may be the motor itself (just having it hooked up incorrectly) or my code.
I’m going to keep working with this circuit, maybe get an L297 to try out, or I’ve know some people who have used shift registers to accomplish the stepping. I’m also going to try this out on some other motors as well. Hopefully I will soon have a nice inexpensive stepper motor driver that other people in the club will be able to use for these nice motors we have.
List of stepper motor resources:
As mentioned previously, I’ve been working on building a painting robot. I believe I have finally completed the construction of it. The only task I have left to complete the robot is the programming.
The robot is comprised of 4 parts:
I had previously completed the motors and painting mechanism. Over the past week I have worked on building the electronics needed to control the paint bot. This evening I was able to complete the wiring. I also ran some tests interfacing with the motors and the rough encoders I built for them.
Programming the robot is going to be an interesting challenge. I am going to be encountering things that I’ve never done before, such as using encoders. The math required in moving the painting mechanism connected to the motor by 2 none orthogonal lines will be interesting. I’ve thought about it some, and I’m hoping it wont be too difficult to implement.
Over the past month or so I have been working on building a painting robot. This robot will be able to paint a wall using spray paint in a graffiti-esque manner. My initial inspiration, and thus similarity in design, was a robot called Hektor. Hektor was a graffiti robot built as a project by Jürg Lehni with help from Uli Franke at écal, the University of Art and Design Lausanne. More about Hektor here and écal here.
I just finished some testing on my spray paint can holding/spraying mechanism. The video below shows the second test of the spraying mechanism. In the initial setup the servo used to depress the spray nozzle couldn’t provide enough downward force all the time. The second video shows an attempt at getting around this issue by the servo pressing on the nozzle from a different direction.
Second Spray Test:
Initial Spray Test:
I will probably end up modifying the spraying mechanism further so it is less of a hack to get it to depress the spray can nozzle.
The following pictures show the can holder and spraying mechanism during the build:
I’ve also finished building motors to move the spray can around. When I get time, I’ll post something about the motor build.
During the previous semester, as part of a class project, we built urban search and rescue robots. We built the robots using the LEGO NXT set. For our robot I built a custom pan-tilt mechanism to mount the camera we were provided with.
The pan-tilt used two servos and a custom microntroller board to interface the servos with the NXT. The controller board also allowed for LEDs (used for illumination) to be turned on and off.
We controlled the robot over a bluetooth link via joystick. It turns out that the NXT brick times out after 15 min no activity and that an open bluetooth does not count as activity.
In short, this project ruined my childhood and made me hate LEGOs. The constraints of the project made it very difficult to build an effective robot. However, a simple combination of wheels and treads let a build a robot to fit the constraints.
We’ve mounted Stairbot in a hanging position so we could perform some testing on its legs. We’ve discovered some issues with our servos, and we keep blowing some of them up. We’re not sure if it’s an issue with the design, or if the servos are bad.
A video of the legs cycling through some motions:
We also have some pictures of the hanging setup:
Friday afternoon we were able to complete the first of four legs of Stairbot. We were hoping to complete more than that, but, we currently only have enough servos for one leg and we’re waiting on the rest to arrive. However, in the meantime, we will work on being able to control this one leg so when we add more, it will be easy to develop gaits. To control Stairbot, we’re going to be tethering an Arduino to a computer for extra computational power, to allow us to perform inverse kinematic calculations.
More updates to follow as more parts come in.