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Project ATAAPR: Andy the Autonomous Arduino Powered Rover - Part 1

By: Charles Gantt | Editorials in Maker & DIY | Posted: Mar 21, 2014 4:52 am

Building Andy

 

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I always like to start my builds by laying out all of the components in a neat and orderly grid pattern. This makes it easy to find parts and lets me make sure that everything is there before I begin the build process. To get started, lay everything out and make sure it's all there. You may notice that some pieces are missing in this photo, and that is because Andy evolved over the course of the build, and some things were added or removed.

 

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The first thing you need to do when building the Magician Chassis is to attach the motors. They attach to the chassis via two small tabs that keep them in line with the robot's center of gravity. In your kit, you will find four small screws with accompanying nuts. These will be the screws that hold the motors in place.

 

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Unfortunately, the wires that were soldered to my motor were very lose and broke off during installation, so I had to solder them back on. I took note of which direction the wires would feed into the chassis and soldered them with a bias to that direction.

 

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Once the solder cooled, I secured the wires to the motor's housing using some hot-melt glue and then proceeded to mount the motor to the chassis using the small tabs and screws. You will notice that I went a step further and glued the wires to the chassis as well. This is not a necessary step and was just an extra precaution I took as Andy will be handled by many people in the next few months.

 

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With both motors mounted and secured, it is now time to move on to the rear "wheel" support. Notice how I placed the nuts to the inside of the motors. This made attaching the second motor a little harder but was well worth it for appearance's sake in my opinion. Be careful not to tighten the screws down too tight as it will crack the acrylic tabs and ruin the entire kit.

 

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With the motors mounted, we can move on to mounting the rear omni-ball support that will help our robot stay stable when traversing the course we will lay out later for him to navigate through. The omni-ball mounts consist of two 25mm long stand offs, four screws, and the omni-ball. Line them up with the correct holes on the chassis and screw everything down; remain mindful not to tighten down the screws too much.

 

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With the omni-ball mounted, we can move onto mounting the battery pack. The kit's official directions say to screw this down to the chassis, but I found that to be difficult as it requires disassembly of the robot to change the batteries. A better solution is to use Velcro to allow the battery pack to be easily removed from the chassis without any disassembly.

 

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If you cannot tell by now, I use hot glue for everything and, over the years, have found it to be the best method to glue Velcro to plastic surfaces. In the image above, you will notice that I used a long strip of Velcro on both surfaces. In hindsight, I would recommend using a long strip of the hook side of the Velcro on the robot chassis and a smaller 1-inch piece on the battery pack. This provides enough grip to hold the pack but leaves it loose enough to be easily removable with just two fingers.

 

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With the battery pack now securely in place, we can attach the wheels in preparation for adding the top half of the chassis. Make note that the wheels are indexed to the axles by the flat spots on the axle and wheel hub. Since all of these parts are extrusion molded, it is best to use a file, piece of sandpaper, or hobby knife to remove the mold seam from the parts for a better fit.

 

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I have built Andy several times over the last few months, and I have taken notes each time on how to do things easier and make the entire project look cleaner when finished. The battery pack we installed earlier is used to power the Arduino via a barrel jack, and the connector on the end is too fat to fit through the holes in the Magician Chassis, so a little modification is needed to make things fit. Luckily, only a small tab needs to be removed, and quick work of it can be made with a Dremel. Alternatively, a file could be used, but the Dremel is much faster.

 

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Using a cut off wheel on the Dremel rotary tool, cut two small slices into each end of the tab and then do the same thing on the reverse side of the chassis. Use a pair of small diagonals or nippers to remove the now weakened tab.

 

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You can leave the hole like this if you chose, but I like to clean things up a little and make modifications look as close to factory as possible. I used a diamond bur bit to remove the excess material in the newly enlarged slot. This only took a minute or so to do, and the result is a clean slot to pass your power cable through. This entire step is not necessary, though, as you could just pass the cable on the outside of the chassis frame.

 

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Now we need to mount the Arduino board to the upper chassis. You can use mounting tape for this, but I like to use the provided stand-offs and mount the board the proper way. It will take a little fine positioning to find the exact location where the holes on the Arduino line up perfectly with the holes on the chassis, but they do line up. You will also notice that I have already mounted the micro-breadboard to the chassis during a previous build. I used 3M heavy duty mounting tape, which proved impossible to remove for this build.

 

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If you position the micro-breadboard flush with the rear edge of the chassis, the Arduino should but up to it perfectly when mounted. Use 3M mounting tape as the included double stick tape is just not strong enough to hold a good bond. Once everything is lined up nicely, you can secure the Arduino to the stand-offs with the supplied screws.

 

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Flip the top half of the chassis over and attach the 25mm stand-offs to the chassis mounting holes as seen in the image above. It is important to use all of the mounting points for added strength and rigidity.

 

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Before we mate the two halves of the chassis together, we need to install the servo that will sweep the ultrasonic sensor to "look" for objects in the path of the rover. I used a standard-sized hobby servo for this and mounted it to the chassis using M3 x 40mm screws. The screws did not fit well, so I had to modify the chassis slightly with the Dremel tool again.

 

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With the screws in place and tight, the servo has been securely mounted. It's worth noting that my servo had a fairly long cable and I had to Dremel out the front hole in the chassis to fit its connector through. This took just a few moments and made for a very clean install.

 

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Here is where you will notice one of the big changes I made. The original Arduino I mounted to the chassis was not an Uno R3 compatible version, and this did not allow the Arduino Motor Shield R3 to fit, so I had to substitute this Arduino-compatible board from SainSmart that I had laying around. It is an R3 design, and everything is pin-to pin compatible with an official Arduino Uno R3. Here is where I began to route the various wires through the chassis. You can see that I have pulled the left motor wires through one of the slots in the board and that the power cable is also routed through the hole I enlarged. Flipping to the other side, and you can see how I routed the servo cable to the breadboard and used header pins to connect it.

 

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I also connected the two halves together at this point but forgot to take photos of the process. It is as simple as aligning the standoffs with the proper holes on the bottom of the chassis and screwing them together while remembering not to make things so tight as to break the fragile acrylic.

 

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