Welding cast iron brackets

     Today, 2 brackets that hold up a side shelf on our wood stove broke off, so i took them into welding class to see if I could fix them. I was worried they wouldn't weld well, as they are made of cast iron, and neither me, nor my welding teacher knew if it would work. To my surprise, I easily joined them with a MIG welder, and grinded the weld so it was flush with the rest of the piece, then polished it off. Here's a picture I took after I did the first one. It was much easier then I thought it would be, and I am quite pleased with the final product.

Offroad Truck Bumper Part 1

     I've decided to build my own bumper for my truck that will increase it's capabilities, allowing it to be more agile over rough terrain. I've looked into buying a bumper, but there aren't too many available for the 97-03 generation of F-150s, and all the one's I've found are highly expensive. The style of bumper that I've chosen is prerunner/baja. These bumpers are widely used in desert racing and offroading in areas such as Mexico and Southern California.
         




The main point of these bumpers is to improve the clearance of the front end. Normally, if you were trying to drive your truck from flat ground onto a steep incline, the bumper would hit, and you'd get stuck. These bumpers expose much more of the wheel, thereby allowing the truck to handle drastic changes in incline.  




      
     
     To build my bumper, I would first need to find a way to mount it to my frame. The old bumper was bolted onto 2 large brackets that were welded to the end of the frame. To mount my bumper, I would need to chop the ends of the frame off to allow the skid plate to have shallower angle, which will keep air resistance to a minimum.




    

    First, I drew up some designs for the mounting brackets of my bumper. I then cut out the pieces I would need with a plasma cutter. I used 1/4 inch iron, as it would give my bumper a good strong base to sit on.
         





    


   
    I used a mig welder to join the pieces together, and once I had both brackets built, I arc welded a piece of tube in between them to get the width right.

     

Robot Arm: Controlling the servos

Each servo connects to the SSC-32 board using 3 wires. The VC(Red) and Ground(black) wires provide the 5 V DC voltage to power the servo.

The third “Pulse” wire supplies a 5 volt control pulse signal that is repeated 50 times a second (every 20ms). The width of this pulse determines what point the servo rotates to, and can be from 0.9ms to 2.1ms long. For example,an ASCII command from the computer to the SSC-32 control port such as “#2 P1500” would tell the controller to send Servo #2 a signal consisting of 1.5ms pulses which would move the servo to move to it centered position.

The Oscilloscope lets us actually see the pulse by freezing the screen, allowing us to measure it. This is how the Oscilloscope shows the 50ms 5 Volt pulses to the servo.

The black permanent grid squares on the Oscilloscope screen are called “Graticules”, and the numbers at the bottom show the units. In this setting, each graticule is 10 ms wide and 5 Volts high. The two dotted lines are part of the Oscilloscope's measurement tools. The Oscilloscope allows these to be moved to allow vertical or horizontal measurements, and the number at the top op the screen represents the distance between them(20.0ms). The time scale of the scope can be adjusted to look at one pulse and make more accurate measurements.

Below is what the .75ms, 1 ms and 1.5 ms pulses look like for the commands “#1 P750”, “#1 P1000” and “#1 P1500” are sent. 

Using the basic commands the Servos moved very quickly but there is a longer command that allows you to control the speed that they rotate into position. By adding a “S” parameter, the movement speed of the servo can be adjusted. The SSC-32 manual does not explain how this works, but using the Oscilliscope we were able to see how the SSC-32 slowly adjusted the pulse width when the command “#1 P700 S100” was sent (note that the the previous servo position was “#1 P2300”). The “S” value sets the movement speed in us/sec.

Here is a video displaying the changing pulse width.

Robot Arm: The SSC-32 Servo Controller

       The servos on the robot arm are controlled by a controller board called a SSC-32. 

       Here's a diagram from the manual detailing each of its components. 

       As you can see, those pins along the bottom are the connection points for a servo motor. One pin is ground, one pin delivers power, and the remaining pin delivers the pulse that moves the servo. The area of the card that says "Baud" is where the speed that data is passed is selected using 2 jumpers. As you can see in the photo, both jumpers are in, which means that the card will operate at the maximum speed of 115.2 Kilo Bytes per second.