Remote Control Micro-Robots― JAMECO PART NO. 2170505 Experience Level

17 Pages·2012·1.57 MB·English

Remote Control Micro-Robots― JAMECO PART NO. 2170505

Experience Level: Intermediate | Time Required: 2-3 Hours

Pingbot is a very small (38mm diameter), USB rechargeable, programmable, musical, remote control robot designed for maximum fun
and dance ability.
I've built a few experimental robots in the past and, to be honest, they all looked the part. They were nothing more than circuit boards
with wheels glued on. They did help me learn, but they just didn't feel like completed robots. The main purpose of this project was to
combine electronics and 3D fabrication into a robot complete in both form and function. A fun robot with a sleek look and a bit of
personality. The second goal was to make the robot as small as possible, smaller than half a ping-pong ball (hence the name).
In this Instructable I will share what I've learned while creating the Pingbot. Included is information about PICAXE Micro-controllers,
surface mount soldering, PCB design, Autodesk's 123D 3D design software and 3D fabrication, rechargeable lithium-polymer
batteries, as well as a few painting techniques.
Included are schematics, a PCB layout, PICAXE code, 123D model files and pictures of the construction process. You will also find a
wealth of links to detailed information that is relevant to the project, as well as suppliers for the parts used in the Pingbot.
Required tools and parts:
 Fine tip soldering iron and solder
 Solder wick and flux
 Side angle wire cutters
 Work vice or clamp
 Jigsaw
 Tweezers
 Heat sink clip
 Sandpaper
 Spray paint
 Black, brown and orange acrylic paint
 Masking Tape
 Super glue
 Magnifying lamp (optional)
 Paint rag/paper towels
 Inkjet transparencies
 Plate Glass 8.5 x 11 x 1/4 "
 Rubbing alcohol, nail polish remover, ammonia, denatured alcohol
 1 USB micro USB SMD Female Connector (Sparkfun #PRT- 08533)
 1 USB 2.0 Female connector
 1 Right angle switch (Sparkfun #COM-10860)
 1 LiPo Battery- 3.7 V 110 mAh (Sparkfun #PRT- 00731)
 1 MAX1555-Lithium Ion/Polymer USB Battery Charger IC (Sparkfun #COM- 00674)
 Needle nose pliers

Kit Includes:

Part No. Qty. Description
35991 5 DIODE
94967 5 TRANSISTOR
156751 1 CIRCUIT BOARD
156734 1 POSITIVE DEVELOPER
616438 1 PCB ETCHING SOLUTION
109576 1 HEADER
256365 2 VIBRATING MOTOR
2007302 1 SURFACE MOUNT RESISTOR
1555104 10 LEDs
1584976 10 LEDs
1879563 10 SMD RESISTOR,3.3K
1986828 3 SMD RESISTOR,150 OHM
2011571 1 CAPACITOR
2078944 10 SMD RESISTOR,10K
2097088 1 TIN PLATING COPPER KIT
2109691 1 IR RECEIVER
2117430 1 PIEZO BUZZERS
2135064 1 USB CABLE

Step 1 - Body Shell 123D Design and Fabrication
The outer shell for Pingbot was designed using Autodesk's FREE 123D 3D modeling software. It took me about a week of fiddling
around with the program and referencing the tutorials before I got the feel for it. Once I had a handle on the basics, I chose a material
and created the final model. The model was saved as an STL file, a common 3D model file type, and uploaded to 123D for fabrication.
The completed model along with a version containing the separated components is both available in the 123D gallery, where they can
be viewed in an interactive 3D preview. They are also included with this Instructable.
Choosing a Material
It is important to choose a material before you start working on a model as each material has different guidelines that you must follow
while you are designing. The materials vary in the minimum wall thickness, minimum detail size, flexibility, and other properties. Some
materials are weaker than others; large models made from them may need inner structure to support the weight.
I chose to have the shell for the Pingbot printed from the Durable Fine Plastic. This material is strong enough to be used as a working
prototype and its minimum detail is a minute .2 mm. It is more costly than other materials, but since the cost of a model is partially
determined by its volume, the shell was incredibly inexpensive to have fabricated. All totaled, it uses less than 1/3 cubic centimeter of
material.
Creating the 3D Model
Although it was printed as one solid piece, the 3d model was made from separate components that come together to make a
hemisphere. This was necessary as it allowed the edges of each of the parts to be rounded off.
To begin I created a hollow hemisphere with a 1mm wall thickness. I then copied/pasted the original shell, drew new shapes, and
extruded these new shapes to subtract (and intersect) from the hemisphere. After completing all the parts I beveled the edges to
create the seams. I've included a couple of pictures of the process.
While designing this robot's shell it was important to remember to add holes for the components that needed to be accessed from the
outside. For the USB connector and micro-switch I use the PCB design along with the components' data sheets to determine where,
and how big, the access holes needed to be. I also added some holes in the back to help let out the sound from the piezo speaker
(the speaker was plenty loud and these holes were likely not necessary).
Upload and Fabrication
In order for a model to be printed, all the separate components need to be welded together to create one solid piece. Once this is
done It can be saved as a STL file and uploaded for printing and sharing. (You will need to be logged into 123D to be able to save as
an STL.)
This video is of the Object Connex 3D fabrication machine, which is likely close enough to the model of machine used to create the
Pingbot shell. It demonstrates how the machine prints the model in layers along with a support material. When fabrication is complete
the support material is blasted away leaving the final piece.
Step 2 - Painting the Base Coats
Painting the model adds another layer of personality to the robot and makes the overall project look more complete. I wanted my
Pingbot to look cute, of course, but also wanted it to look a bit beat up and weathered.
Surface Prep
The surface of the 3D printed model was fairly smooth, but I decided to sand it a little to help the paint stick. I used some 400 grit
sandpaper to sand the entire surface, and then followed by dipping the same piece of sandpaper into water and sanding the model
again. The model was then completely cleaned using a toothbrush, water, and rubbing alcohol. This cleaning removed any dust, oils,
or other smudges that might have prevented the paint from adhering.
Base Coats
I began by painting the entire shell with a few light coats of matte black spray paint. Normally I would have painted it with a primer first,
but the black paint was the type made for using on plastic. After letting these coats dry for a full day, I used a thin masking tape made
by Nichiban to mask the areas that I wanted to remain black. I like using this tape because it smoothly bends around curves and its
adhesive leaves essentially no residue on the model. I made sure to tuck the tape into the seams and roll it around the edges of areas
that stuck out from the main sphere. Blue painter’s tape was then used to cover the larger areas.
Nichiban can be difficult to find and you may need to resort to an alternative. I do like blue painter's tape, but the factory cut edge on
its sides is fairly rough. To get a crisp edge from the tape you need to cut the rough edges off with a sharp blade. It also helps to cut it
into small, manageable strips when working on smaller jobs.
The masked model was then painted with a several coats of gloss blue. I know it's difficult to resist immediately ripping the masking off
to see the new paint job, but doing so too early can lift and stretch the paint. Wet spray paint can stay a little rubbery for hours after
being applied, so I made sure to let these coats dry an entire day before lifting up the masking tape.

Image Notes Image Notes
1. The mask has been removed and the model is now ready for detailing. 1. Sanding the 3D in preparation for painting.
1. The black base coat is painted directly on the clean, sanded shell 1. Masked areas will be protected from blue paint

Step 4 - Detailing
I decided to add some numbers to one side of the shell to represent this being my first complete bot. I printed some numbers out on
plain white paper and placed a wide type of Nichiban tape over them. Then, using an exacto knife, I carefully cut the numbers out,
peeled the tape from the paper, and delicately applied the mask to the shell.
After masking off a sizable area around the numbers, I used a stiff brush to tap yellow paint into the stencil. When wet paint is used on
stencils made from masking tape it has a tendency to soak underneath the tape and leave a rough edge. This can be avoided by
dipping the tip of the brush in paint, wiping some of it off on a paper towel, and then dabbing the brush on the stencil. I needed to
apply several coats to get the yellow to stand out against the blue, but it was worth the extra effort.
Again, I made sure to let the paint dry completely before removing the tape.

1. Dabbing the paint in will make for cleaner edges later on
Crumpled newspaper simulates weathered paint.

Step 5 - Weathering
I really like weathering just about every project. By simply dabbing watered down acrylic paint on the model and dry brushing specific
spots, a project can transcend from looking like a toy to looking like the 'real' thing. It also does a fine job of hiding mistakes,
scratches, and marks from bumping into things. If you prefer a cleaner look, you can of course skip this step.
Dry Brushing
I dry brushed a metallic silver acrylic paint over the entire surface of the model. This was done by dipping the brush into the paint and
then wiping the paint off on a rag.
Once there was next to no paint left on the brush, it was used to go over the edges, holes, and rough spots of the shell. The silver
paint caught on the higher surfaces and made the base coats look like they had worn off to reveal metal underneath.
Applying the Wash(es)
To start I got some brown, orange, and black acrylic paint, something to mix them in (I prefer pickle jar lids), and a few paint rags. I put
a wee tiny dab of black, and we tinnier dablett of brown into the lid and added about one tablespoon of water. This was well mixed and
then soaked up with a rag. I gently dabbed the wash into the crevices and corners of the model. After a few seconds of drying a
crumpled up piece of cloth was used to dab up the access paint.
The process was repeated with several other shades and hues of washes that were made with different combinations of the paints. If
you're in an experimental mood try mixing some green or red in there why not. The idea is to make the model look like it's been sitting
in the backyard for a few years collecting dirt. I like to look at pictures of weathered metal for inspiration.
After I felt that I had added enough grit, I added two coats of flat clear spray paint to hold the finish.
1. Dry Brushing metallic silver paint onto the shell

Step 6 - Circuit and Schematic
The Brains
A 08M2 PICAXE micro-controller serves as a mind for the Pingbot. This chip is incredibly easy to program, it automatically
understands universal TV remotes, it's cheap, and it has the ability to play music with the tune command! On top of all that there is an
incredibly large amount of documentation and instructions available directly from the PICAXE website.
Once it is soldered into circuit the 08M2 can be reprogrammed with a USB port, the AXE027 serial converter cable, and a micro-USB
cable; the chip does not need to be removed from the PCB. This makes it simple to change the behavior of the robot and experiment
with different commands.
Remote Control
The 08M2 uses a 38Mhz IR receiver to decode up to 17 commands from a universal television remote. You can buy the IR receiver
online, or you can scavenge one from an old appliance. Pretty much all older DVD players and VCRs were made with one of these
receivers.
Power Supply and Recharging
The robot is powered by lithium-polymer battery (LiPo). A MAX-1555 IC is used to charge this battery via the same micro-USB cable
used for programming. When the cable is plugged into the robot, the 1555 connects to the USB port's +5V pin and charges the LiPo
battery. A micro-slide switch connects the batteries ground to the circuit; the battery will not charge while the switch is turned off. While
charging the 1555 lights up the red LED, and then turns it off when the battery is full.
LiPo batteries are very light and hold a lot of energy for their size thus making them ideal for small robots and RC toys. However, if
charged incorrectly, Lithium-Polymer batteries can be dangerous! They must have a charger designed for lithium batteries.
Using a Ni-Cad or NiMH to charge a lithium-poly battery is VERY BAD and can result in explosive fire! The battery and charging IC
used in the project are made to work together. If you want to experiment with other Litho-poly batteries, please do your research first!
Locomotion
Two small pager motors are mounted through the circuit board in such a way that their shafts touch the ground and work as wheels for
the robot. They are controlled by the 08M2 and two 3904 NPN transistors. These transistors receive signals from the 08MX and act as
switches for the motors, turning them on and off. A diode is used across the motors' leads to protect against reverse voltage. For more
info on how this works check out this tutorial with details on this and other useful methods of small motor control.
These types of vibrating motors are readily available online. While shopping you should try to find ones that do not have the weighted
ends that make the motor vibrate, those things can be a huge pain to take off. The best way that I've found to remove them has been
to use a similar sized shaft taken from a dissected motor. With a pair of pliers, I grab the weight attached to the motor intended for the
robot. Then with another pair of pliers, I push the extra shaft down into the hole in the top of the first weight. With a bit of force the
motor's shaft usually slides out.
Personality - Lights and Music
Personality is a great way to make your robot feel like more than a mess of components, and the 08M2's tune command is perfect for
giving a robot a bit of charisma.
With it you can play old cell phone ringtones through a piezo speaker, and have a LED blink along with the music. To make use of this
function the circuit includes a 12mm piezo speaker and two small LEDs. Excess leads cut from previous soldering work are used to
attach the LEDs to the circuit board so that they can be bent into position behind the CD lens eyes.
Schematic
These circuits are found in the MAX-1555 and 08M2 datasheets and manuals with very little modification.

Step 7 - PCB Design
The Pingbot uses a single sided circuit board with wire jumpers soldered underneath. It was made with a type of circuit board that is
coated with a light sensitive film, a developer for that film, ferrite chloride to etch the board, and a tinning solution kit. The components
were then soldered to the board by hand using a fine tipped soldering iron.
Drawing the Circuit Board
Using Adobe Illustrator I created different layers for the traces, components, the grounding plane, and the part labels. Using the
component's data sheets as reference I then drew out all the components to their actual size and arranged them to fit within a 37mm
diameter circle. Traces were drawn according to the schematic to connect the components.
I used Illustrator because I am familiar with it, but the most common way to design circuit boards is Eagle PCB, free software from
Cadsoft. This program can be used to draw out a schematic that can be converted into a PCB layout. The designs and files that it
generates can be printed out or sent to a manufacturer to be fabricated.
Charge LED, I'm Doing it Wrong
While designing this PCB I had assumed that the MAX1555's charge LED should be connected to ground. After I had finished
soldering I did some testing and found that the LED wasn't doing anything. It should have lit up when the robot was connected directly
to a USB port and the battery was charging, but that didn't happen. Turns out the LED should have gone to +V...
To fix this I desoldered and lifted the LED's lead, the one that I thought went to ground, from the PCB and connected it to +V with a
jumper wire above the board. I stuck a dab of hot glue under this LED to make sure the lead didn't touch the ground pad. This error
was corrected in the schematic, but I have not fixed it in the PCB layout.
Instead I've just shown the jumper wire.
Step 8 PCB Fabrication
Safety First
Developing and etching circuit boards at home involves chemicals that are dangerous if used improperly. It is important to always
wear gloves and work in a well ventilated area like outside. Always read the material data sheets and follow the instructions provide
with these products!
Developing the Circuit Board
After drawing out the circuit a photo-positive was created by printing the design onto a transparent film. Most print shops will be able to
do this, but you can also buy a box of the transparencies and do it at home. Different transparencies are made for inkjet and laser
printers, be sure to buy the appropriate type. Also, be sure to print it at a 1:1 scale; I forgot about this and etched the first board before
noticing that the design was too small and needed to start over.
While in a dark room I removed the protective plastic film from the pre-sensitized circuit board and lined the positive up on top of it. To
hold everything in place I put a small plate of glass on top of the positive. The instructions that come with the board say to expose the
board 1ft under a 100 watt bulb for 10 minutes, but I've always needed to go for at least 12.
I prepped the development solution about a minute before the exposure finished. The solution is a mix of 1 part development
concentrate with 10 parts warm water. Cold water halts the developing process and prevents further development. If used at this
point, cold water would essentially ruin the board.
After 12 minutes of exposure I placed the board in a plastic tub with the warm development solution. I gently rocked the tub to keep
the solution moving around. The developer quickly washed away the areas of green sensitized film that were exposed to light while
leaving the circuit traces behind. The board was then run under cold water to complete the development.
PCB Etching
Next the board was placed into a small Tupperware container along with a mix of Ferric Chloride and warm water. Again I rocked the
tub back and forth to keep the mix flowing. After a few minutes the exposed copper was eaten away leaving only the protected circuit
design and the fiberglass board.
The remaining photosensitive coating was scrubbed off the circuit board with nail polish remover and an old toothbrush. It is important
to clean the board really well. If it is not perfectly clean you will be able to see the dirty areas later on, after it is too late.
Drilling the Through Holes
I'm sure there is a standard in what size PCB holes should be, but not knowing it I just drilled them with the smallest bit I had on hand.
I also needed to drill out two larger holes for the two motors. Drilling these holes was easy enough with a miniature drill press, but they
also needed to be angled to allow the motors to act as wheels. To do this I used a small file to shape the fiberglass board. During this
filing I made sure to put the motors into the holes and test the angle until i got it right. It was crucial that these holes be filed to the
exact same angle so that the motors would sit correctly.
I sort of screwed this up and the motors sat lop-sided, causing the shafts to contact the ground at different points. This changed their
speed and one motor ended up being faster that the other and in the long stretch this difference makes the robot veer off to one side.
It is still easy to control and I don't really mind that it isn't perfect, but in the future I will be much more precise when setting motors. I
may even use a protractor.
In the process pictures you will notice that there are some components already soldered to the board before the motor holes are
drilled. I had made another mistake and forgot to drill these holes before I began soldering.
Tinning the Traces
Tin plating makes soldering the surface mount components much easier and it protects the copper from oxidization. To do this I used
a product called Tinnit that I bought as a kit. I began by drilling all the through-holes and thoroughly cleaning the board with more nail
polish remover. Again it is very important to do a good job cleaning the board off.
I failed to do so on this one and you can clearly see finger prints in on the traces. >_<
The dry concentrate was mixed with warm water and microwaved until it reached about 140° F. The board was placed into a plastic
tray with the tinning solution and jostled every 5 minutes. After roughly 20 minutes the copper traces became plated with a micro-thin
layer of shiny tin. Finally, the board was then cleaned with ammonia to remove the remaining tinning residue. The remaining tinning
solution was poured back into the bottle to be reused later.
Once mixed Tinnit only lasts about 6 months. Unless you plan on tinning a few dozen boards in the near future, it is wise to mix it in
small batches. To do this you'll need a small scale to weight out the powdered concentrate and something for measuring fluids. I
divided my concentrate into four smaller batches, which should keep me in the tinning business for the next couple years.

1. Nail polish remover is also green film remover