He has just one thing on his mind….

Originally published February 10, 2010 .


Building My Own Version of “The World’s Most Useless Machine”

Part 1 – Introduction

I have been looking for a good project where I could combine my two major skills; woodworking and electronics. When I saw the YouTube video – The Most Useless Machine Ever! last December I cracked up laughing! And I knew I found the perfect project where I could apply my increasing skills in wood crafting with my already professional electronic skills to make a item that is just plain fun. I will posting my progress of the design and final results. I am planning on making copies for sale on my ETSY store!

Anyway take a look for yourself if you haven’t already seen the video, its been a viral hit on YouTube

Building My Own Version of “The World’s Most Useless Machine”

Part 2 – The Plan

After seeing SaskView’s video I saw a link back to his complete build instructions on the Instructables   Web site where he posted a great set off build instructions. I spent a lot of time reading the instructions and all the great comments. I took a look at all the variations people built and the troubles they had with the electronics. I even posted a few helping tips for some of the electronic questions. I noticed that most people where having so much trouble with the electronics they got around it altogether by just modifying the servo motor and using simple switches bypassing the electronic timer circuits. Well that is a simple solution to a complex problem for sure!. But since I really wanted to apply my electronics skill I went against my general principle of “keep it simple stupid!” and I will be controlling the motor with electronics. In fact I am going to expand the circuit by adding a second timer circuit to give the machine a slight delay before the motor starts. After looking at the the posted example videos I felt it might need a tad delay for effect.

So here is my design check list:

1.  Figure out how hobby servo motors work and how to control them.
2. Design a control circuit that uses a dual 556 timer with one side for the delay and the other side for the motor.
3. Design a nice box to house the machine.
4. Design the mounting for the motor, circuits, battery etc.
5. Design the arm that lifts the lid and turns off the toggle switch.

Seems simple!

Building My Own Version of “The World’s Most Useless Machine”

Part 3 – Obsessed Much? 

Louise has been pointing out to me that I have been totally obsessed with this project. I admit it I am! But on the plus side I am having a ton of fun designing it and have been learning new tools (electronic types) and refreshing my skills. It’s been a very long time since I just played with electronics rather than working in the field for a living. I have forgotten how much fun it is to design circuits which is why I went to school after all.

So one item on my design list I can cross off is how servo motors work. I was rather surprised how little is written about how they really work on the web. Lots about mounting tips and what controllers to use but very little about the guts of the motors. I was curious so I kept digging and found a few pretty good sites:

***** NERD ALERT ***** 
 Read the following section only if you are a nerd like myself LOL

fundamental explanation of how hobby servo motors work from Princeton University


 The second site gave me a big clue about how torque was generated in a hobby servo motor and why one direction will have more than the other director. This is important because on the Useless Machine one direction will be moving the control arm up to turn off the power switch and needs more torque. Basically the position of a hobby servo motor depends on the length of a pulse between ~1ms to 2ms is. A pulse of ~1.5ms will put the servo position in the middle of it’s range. The range is typically 180 degrees of movement. The direction the servo moves with the long 2ms pulses is the direction to chose to the switch.

***** END NERD ALERT *****

So now with a better understanding of how hobby servo motors work I can go about designing my control circuit.

Building My Own Version of “The World’s Most Useless Machine”
Part 5 – SketchUp Model My First Video Blog

I think I need to be committed over this project because I know I have gone over the top now. I created a Google SketchUp model with animation to show how the machine will be built. Actually there was a good reason to make a 3D model and that was to help me figure out all the mechanical stuff. Working it all out in the virtual world is a whole bunch easier than making the actual real stuff. It’s real easy to move or re-size a piece on the fly with SketchUp.

But just to prove just how far gone I am I created a couple of videos and uploaded them on YouTube. One is an animation of how the machine will work. And the second is my video blog on how I used SketchUp to help me design the machine.

Video Blog – How I used SketchUp to help me design this machine.

Let me know how the idea of a video blog works out.

Building My Own Version of “The World’s Most Useless Machine”

Part 6 – Building The Final Prototype 

I actually finished building my final working prototype just before we got knocked off-line last weekend with our crazy wind store. A week later and with a brand new wicked fast ASUS computer my lovely wife Louise bought me I finally has some time to take and edit up some photos of the box. I must admit I am really anxious now to build my first for sale machine now that I seem to have most of the kinks worked out.
Here is a video and slide show I made showing the final prototype.

I had a heck of time figuring out how to make the arm reliably close the micro switch to turn itself off. My original idea was to mount the micros switch on a an arm off the servo motor mount. That idea was fine but the idea of placing on the side between the mount and the battery holder was bad because the arm tended to bounce off the mount and open the switch instead of just settling in the off position. The solution was pretty simple to just move in on the other side of the mount so I was using the shorter length of the arm to hit the switch which naturally has less movement. Now if the slop of system allows the arm to bounce a bit where the switch is hitting doesn’t have enough movement to cause the switch to re-open. Well it worked and the box works very well now! I know the wiring looks a mess. I build the proto circuit on plain perfboard and point to point wired it which took forever to build. My production version will be made on a strip board and will hopefully come out a lot more neat looking.

In case you are wondering the smiley friendly snake is a finger puppet my wife had from her soap making supplies. I think it looked funny and it worked out perfectly. She has a number of other finger puppets that would work as well so I will be able to customize the look.

I all the pieces to size on my table saw using the rip fence and my crosscut jig. I then used my Incra Router jig to make the finger joints and route the dato slots to hold the bottom and top panels. I realized while working on my SketchUp plan I had to make the lid pieces longer than the box to compensate for the saw kerf in the 45 degree split I need cut on the table saw. Another great example of designing in a 3D model before you actually cut wood to save time and money! So that made it a bit more difficult to make rather than the standard way of building the box with the top and bottom attached then to saw off the lid. I ended up in making the lid just a tad too short. My next build I will make it longer realizing I can easily sand it down to the proper length after I cut the split.

You can see the extra length added to the lid on this plan. I will also need to add some height to the box by one finger joint when I build my production model because the space between the servo motor mounts and the battery holder was really tight.

I struggled with how to hold down the access lid a bit until I figured I would just a magnet embedded in the bottom with a metal screw coming down from the lid top. I can fine adjust the screw head till it just hits the magnet and grips down firmly holding the lid quite nicely down. It takes a good amount of force to actually open the lid when you need access to adjust the delay or change the batteries.

So now it’s time to work on the production model. I need to make a compact reliable circuit board, make the box a tad bigger to fit all the components nicely and make sure I get my hinges placed properly. My obsession continues!!!

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