I realized that the h-bridge motor driver I was using for both my front and back motors wouldn’t work because it would go into a thermal shutdown. To fix this problem I wired a separate motor driver that is able to handle up to 3.6 amps to my back motor. The motor that I used for this was a DRV8871 DC Motor Driver. It works very similar to the h-bridge using 2 different inputs to alter the direction of the motor. A minor feature I add to the car was an on and off switch I salvaged from the original car itself. I did this so I would not have to constantly remove and replace a wire every time I had to upload new code to my arduino.
Well, this was a busy week. I managed to build a leg, make that leg move in some kind of way similar to natural movement, and made a few decisions for the future. I first built a leg with a stepper, as shown in the video, but later decided to try it with servos only. It was difficult to make loops for both types of motors, but once I switched to a common motor, things began working much better. Since the video was taken, the new servo leg can perform much more natural and walk-like movement. I also researched how to gain more precision from a servo to make it less twitchy. I found a few ways to change the PWM settings of the servo to allow rotations of less than 1 degree. I also looked into new servos to use for the project later on, as well as servo controllers. The servo controller I decided on can move the servo at 0.025 degrees at a time, which is incredibly precise. I ordered more powerful and nicer servos with the controller. An added benefit is that the controller allows me to control all 8 motors with only 2 wires from the Arduino. Moving forward I plan to work on the math required to implement my dorito shaped walk cycle into my code, as well as begin planning the manufacturing of the robot.
This week we ordered the laser for my project. We ordered a 5w 450nm Diode and a G-2 collimation lens. The original concept of building a gantry with v-slot rails was to expensive and had many moving parts. I decided to change the design to use mirrors. There would be two mirrors attached to servos, moving the servos would move the mirrors which would move the laser over the surface. I think this layout will be more interesting to build and to utilize.
This week I researched Lasers.
I began my quest by investigating some popular laser cutting forums to see what powers and wavelengths are best. Power is in watts and it determines how much heat is transferred to the material, and thus how much material it can cut through. I chose a 5w laser as my first choice as that power ca cut through 1/8 inch softwood, and engrave some metals. My second choice laser is a 2w diode, this laser is not as powerful, but can accomplish the same feats just with a few more passes. Next I researched wavelength. Wavelength affects how much of the laser’s energy is absorbed by the material that it is cutting and how much is reflected. The laser I chose is roughly 445nm, this is in the blue spectrum. This wavelength is quite popular and therefore cheap, and also has good performance cutting darker materials and lighter colored materials.
**Note: The spelling of laser with a “Z” is incorrect**
This week was short for me because I was only in class Monday and Friday. I did however in that short time get the h-bridge motor control to control a D.C. Motor forward and backwards. It has two buttons one is on and off and the other is reverse. It also has a potentiometer which controls the speed of the motor.
I am still trying to figure out how to get the accelerometer to read data on the computer. There is somthing wrong in the code and i am taking it apart piece by piece until i can get it to just read the data corectly. I also when to Walmart and bought a rc flipper car so we can start to get a idea on how to program that.
I spent the majority of this week looking for and implementing a sufficient power source for the motors. Before this I was using a power supply with a very long cord that I had to use as a tether. I went with a rechargeable 9.2 volt battery which will give me 0.6 amps. Because of the battery’s size and how small my car is, it was difficult trying to find a safe place to put it. To fix this I decided to cut out the pegs that were originally used as screw holes for the outer frame. This is what my arduino board was sitting on. The pegs were conveniently very close in height to my battery so I simply zip tied the battery down where the pegs were and I now have my arduino board sitting on the battery.
This week, rather than working on the quadrupedal robot, I worked tirelessly on the Mars Rover Project. This is an extra curricular project that I and a team of a few others decided to undertake. We had a presentation this Friday at Spring Grove High School, and I successfully hacked a consumer RC Tank to be fully controlled by an Arduino. Over the week, I worked on soldering connections to the controller board and transistorizing all switches of the controller to be utilized by the Arduino. Next week I plan to continue work on the quadrupedal robot and make a complete working leg. Moving forward with the Rover, I plan to complete the electronics package for the lander and bug fix the tank for flawless deployment every time. I will likely do this during Flex or Period 4, rather than during Robotics in Period 1.
This week in robotics I decided to go with the staircase layout for my donkey kong robot project. I also figured out the basic dimentions of the arena and I am now working on programing a accelerometer to read data when i move it.
I spent this week learning more in depth motor control with the h-bridge and implementing that into a remote control car. I stripped the remote control car of it’s circuit board and left it with its structure and the front and back motors. I then replaced the circuit board with my arduino computer. I have taken full control of the back motor which allows me to program the car to move back and forth. I wired the front motor in but still have yet to test it. I should be able to achieve full control of the car very shortly. This experience will really help me in the development of my autonomous obstacle avoiding car.