My Thanks to Mr. Clavel

I spent some time working on this backburner project over my Christmas vacation. It’s nowhere near finished, but it functions, so I thought I’d share what I have.

This robot arm configuration is called a Clavel Delta Arm and where you might think of a typical robot arm composed of a series of links, this is a parallel design. Well, strictly speaking, my robot arm is missing the parallelogram lower links that are a key feature of the Reymond Clavel design, but that’s a future improvement and I’ll get there.

My goal for this project is to develop the mechanics and controls to make this arm functional. I’ll be adding the parallelogram lower links and developing the kinematic equations so I can drive this arm by cartesian (x, y, and z position) or cylindrical (r, theta, and z position) coordinates.

That was my project day!

If you liked this project, check out some of my others:

Instant Parade!

The ThrAxis – Our Scratch-Built CNC Mill

Give Aging Technology a Chance

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Instant Parade!

This contraption is fun, in a box, with flags (Sheldon Cooper would be proud). The basic idea is, you can put flags for any occasion in the holders, push a button, and BAM! Instant fanfare with flags waving everywhere.

The Instant Parade was inspired by many things. The first and foremost was my wife. While stuck in traffic one day in her Scion Xb, we noticed that we had fallen in line behind another Scion Xb and she said “it’s like we’re in a Scion parade.” With that one statement, we had invented our own commuting game where we would exclaim “Scion Parade!” whenever we found ourselves in front of, or behind another Scion. This has since evolved to include the “Super Scion Parade!” for other Xb’s of the same color as ours and “Scion Mob!” if we find ourselves in a group of Scions. I also drew inspiration from the hit movie “Cloudy with a Chance of Meatballs 2” where Flint Lockwood would exclaim “Celebrate!” and his trained monkey Steve would hit the big, red button on Flint’s Party in a Box invention. The resulting explosion of colored paint, confetti, balloons, and stunned faces put us on the floor laughing. When we put those two things together with Independence day as an opportunity to try something new, the instant parade was meant to be.

Some important considerations for this project were that I wanted the flags to be changeable, so if we wanted to use it for the Super Bowl, the World Cup, or just in a Scion parade, we could. I needed the flags to wind up when they’re done waving around so they aren’t laying loosely on the table . Finally, the whole thing needed to be battery powered so I could take it with me on the go. After all, a parade isn’t a parade unless it’s moving.

Instant Parade Lego Prototype

Lego prototype

I started designing with a Lego prototype. This helped me figure out the layout of the mechanism and what would work and what wouldn’t. For example, the gears in the wind up mechanism would constantly slip teeth because the shafts were too loose, so I knew that I’d have to make the bearings with tighter tolerances.

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Pictures from the build process

To build the frame, I used some scrap 3/16″ plywood material and some 3/16″ dowels. This allowed me to set the width between the two servo mounting plates as I went. I used two HS-485HB servos to wave the flags around and a hobby motor I took out of an old remote control car steering mechanism as the wind-up motor. The motor doesn’t have a lot of torque, so I had to change the gearing ratio from 10:1 in the Lego model to 1:3 in the final build. The bearing assemblies are made from 7/32″ OD x 0.014″ wall aluminium tube cut to 1.75″ fit inside a 1″ piece of 1/4″ OD aluminium tube with the same wall thickness. The center bore of the 30-tooth gears I used had to be reamed to 7/32″ (with a cordless drill and a drill bit) to fit on the 7/32″ tubing. I got lucky that my drill bit is just the right size so the gear has a snug enough fit that it doesn’t slip when the flags are being wound. Not all drill bits have the same tolerance, so if you’re not that lucky, maybe try again with a different drill bit on a different gear. With the 7/32″ sleeve and gear on the flag pole, I drilled two 1/16″ holes, one at either end and used solid 22Ga wire and some #10 washers to hold the 1/4″ tube captive, but freely rotating. Finally, I mounted the bearings on the servo horns with the mounting screws supplied with the servo and a rectangular piece of the 3/16″ plywood with a V-groove filed in it to keep it aligned with the outer bearing shaft. I had to take care not to over tighten the screws otherwise it would pinch the bearing and prevent it from rotating. The last part of the build is the rectangle of poster board I used as the trough to hold the flags when they wind up.

The servos and motor are driven by an Arduino Uno SMD. From the start of the program, the servos are at their home position in the poster board trough, then they dash to about 30 degrees, then wave back and forth using a sine function, giving the waving a natural fluidity. Each flag waves at a different rate to add some dimension to the motion. After a period of time, the flags return to their home position in the trough. The wind up motor then runs for a set amount of time and the whole thing just stops, waiting for the reset button to be pushed, starting the sequence all over again.

Instant Parade

Instant Parade!

Like any other project, there’s always things that can be done to improve it. In this case, I’d like to change the program so the dash to 30 degrees at the beginning and the return to home at the end are smoother and more controlled. This will reduce the current draw on my batteries and give the whole motion a more fluid, natural appearance. I also think the functionality of the Arduino is wasted on the simple requirements of this project, so I’d like to use a simpler microcontroller like perhaps the Picaxe-08M2. I think I can improve the winding of the flags by changing the shape of their trough. I’ll have to experiment to find out if this will work. Finally, I’d like to make a cover for the mechanism to give it a cleaner look and to make it easier to carry around with me.

That was my project day, how was yours?

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