Archive for the 'Projects' Category

NickelBot – Complete

The NickelBot is complete and it works great. The goal of the project was to create an easily portable machine that creates low cost items that could be given away at events like Maker Faires. I think it has completely achieved that goal. The nickels are purchased from Amazon and cost about $0.08 each.

Here is a video that explains the machine.

Results

It is quite reliable and the cycle time is is just about right at 1-2 minutes per nickel. I think the engraving quality is quite good. I ran it at the Chicago Northside Maker Faire last weekend. It made about 60 nickels without any problems. Here are some of the nickels it made.

Mechatronics

The NickelBot uses (2) NEMA14 stepper motors in a T-Bot configuration. These drive a single GT2 6mm belt. The linear bearings are (2) 6mm rods per axis with (1) LM6LUU per rod.

To handle the nickel loading and unloading, it uses a single micro hobby servo. This servo  connects via a 0.03″ brass wire to a clamp. The firmware has (3) positions hard coded for the servo for fully open, nickel support only and supported plus clamped.

All 3D printed parts are PLA printed on a Lulzbot TAZ6. The colors just represent the color that happened to be in the printer at the time.

The Laser Module

The laser module is a 3.5W peak, 450nm (blue) laser. It comes with a laser power supply that has a 12V power input and TTL laser control input. It also comes with a 12V 5A power supply. I bought it a few months ago from Banggood.com when it was on sale for about $70, but they are typically around $99.  I control the engraving power with a 5kHZ PWM from the microcontroller.

Controller

I used a PSoC5 development board as a plug in on a custom PCB.  I knew adding an additional, accurate PWM for the servo was going to be vastly easier on the PSoC5 vs. an Arduino.

This dev board has a built in programmer debugger that makes firmware development very easy. It is great to be able to set breakpoints and check values with the debugger. I have have a another blog post with more details on this here.

Firmware

The firmware is a modified version of my PSoC5 Grbl port. The only modification needed was the code to handle the clamp servo. Rather than adding special gcodes for the clamp, I simply re-coded the M7,M8 and M9 coolant commands. I did this because all of the parsing and protocol issues were already done.  Each command represents one of the clamp positions.

I may post the source code on Github soon.

Calibration

The machine has (2) home switches (X and Y). A homing sequence needs to be run each time you power up the machine.  All other locations are referenced to this location. A one time  calibration is done to locate the following locations.

  • G54: G54 is the the default work offset. I decided to use the center of the nickel as the 0,0. I jogged the machine visually until the nickel looked centered. I then set the G54 location with this gcode line”G20 L10 P0 X0 Y0″. I made a target shaped graphic that I used to test engrave this location(see above). I used a caliper to measure the centering error, jogged that amount and reset the 0,0. I did this about 5 times until I was satisfied with the centering.
  • G28: I used the G28 location as the location under the nickel hopper. You jog to the location and set it with “G28.1”.
  • G30: I used the G30 location as the position over the eject chute. This is set with the G30.1 gcode command.

Software

I am using LaserGRBL.

This is a great program for this application. It does everything, starting with a bitmap image, to gcode sending in one application. It also has some macro (multi-line gcode) buttons that are very handy. The only drawback for some is that it is Windows only.

Here is an example of the macro to get the nickel.

G90G0X0Y0 ; rapid move to absolute 0,0
M9 ; loosen clamp
G28 ; move under nickels
G4 P0.75 ; wait for nickel to fall and settle
M7 ; close clamp
G4 P0.5; wait a bit
G0X0Y0 ; return to 0,0

Source Files

Possible Improvements

  • Interlock switch: Right now there is no interlock switch for the door. If I make a new PCB, I will add a provision for that. I’ll probably just break all power to the laser module.
  • Nickel Flip: Right now the nickel always comes out of the chute upside down. This is not the best presentation. This was a compromise to make the machine as small as possible. The nickel has to fall between the Y rods. Rather than makethe distance between the rods wider than the nickel, I designed and aligned the clamp/support system so that one side of the nickel falls first and goes between the rods closer to vertical.  There is a probably a way to design the chute to catch the nickel before flips over completely or re-flips it back.
  • Software:
    • More automation: LaserGRBL has macro buttons for the nickel feed and eject features, but it would be nice if that was automatic. They have added a gcode header and footer feature to the roadmap. Right now you can generate the gcode, save the file and paste the nickel handling code in an editor. That file is then fully automatic.
    • Customizing: It would have been fun to easily add names, etc to nickels for people.

If you want to be notified of future blog posts, please subscribe.

Wooden Nickel Engraver Update

I got a chance to do some work into this project and I made some progress.

The X,Y mechanism is a free standing H-Bot. Here is a bottom view. You can see the Y home switch and the bottom of the servo to control the nickel.

Here is a top view of the mechanism. The yellow clamp piece opens partially to create a platform (ledge) for the nickel. This slides under the nickel feed tube and a nickel drops in. The bed is extra wide, so there is always something supporting the nickels in the feed tube.

The servo then clamps the nickel by pushing the tang on the yellow clamp piece into the nickel. Once the engraving is complete, the clamp completely retracts, removing the ledge. The nickel falls through into a hopper that is accessible from the front. This allows for a fully automated process and you don’t need to open the machine.

Here it is with a nickel in the clamp.

I have a temporary enclosure for testing. This supports the XY mech. You can see the nickel feed tube and the laser module support bracket. Currently it is open and a little larger than necessary to make it easy to test. It will eventually be cleaned up and get an access door with a window.

The next step is to work on the firmware. I plan to use Grbl in Core XY mode. I need to add a way to control the servo and figure out some commands to  control the nickel handling.


If you want to be notified of future blog posts, please subscribe.

TWANG Shield Rev. 2

I recently ran out of the original TWANG shields. I took the opportunity to make a few changes.

Audio Jack

The internal speaker is powered by the Arduino I/O pins. This limits it to the low voltage and current that those pins can provide. In normal environments that sound has plenty of volume. I have used it at some very loud events where that sound level is not loud enough.

This version adds a standard 3mm (1/8 in.) audio jack. You can connect this to a powered, external speaker.

Power Capacitor

Some old LED strips like the WS2812 are very sensitive to voltage spikes that might come from lower quality power supplies at turn on. They recommend adding a large capacitor to reduce voltage spikes.  A larger 1000uF capacitor has been added to the PCB, so you do not need to install it externally.

Life LEDs

The TWANG firmware supports the use of remaining life LEDs. The firmware normally shows the remaining life LEDs on the LED strip.  This has the advantage of making it easy to change the lives per level without having to change your hardware. On version 1, there was a place to install (3) life LEDs, but the LEDs were never installed.  This version removes that feature.

Where to Get One

They are currently for sale on Tindie.


If you want to be notified of future blog posts, please subscribe.

TWANG32 – An ESP32 Port of TWANG

 

I ported the TWANG game over to ESP32. I wanted to do this for several reasons.

  • Cost: The ESP32 is generally lower cost than the Arduino Mega
  • Speed: The ESP32 has a dual core 80MHz processor vs. the 16MHz Arduino Mega
  • Memory: The ESP32 has much more RAM and program space to allow more features, levels and audio files.
  • Physical Size: A Mega is very big. This creates a large enclosure that takes a while to print. The smaller enclosure is also more portable.
  • DAC Pins: The audio capabilities on the Mega are very crude and basically limited to square wave tones. A DAC can output digital audio. Currently I am just using a similar square wave tone to the Mega, but it works much better for adjusting the volume.
  • Wireless: The ESP32 has Wifi and Bluetooth. This will allow easier (smartphone) interfacing for options (brightness, volume) and level pack uploads. I also want to consider dual player battle type games with linked controllers.

The Audio

The original TWANG bit banged audio directly from I/O to a speaker. This was super simple, but the volume at max was not loud enough for noisy environments. The ESP32 I/O is a lower voltage (3.3v) and less current, so something needed to be done. I prototyped with a PAM8403 based amplifier (~$4 on Amazon). This worked great, so I added that I.C. to my shield. The volume is controlled by the amplitude of the DAC.

The Shield

I made a shield to simply the wiring and provide a stable way to mount the ESP32. I used a NodeMCU 32S development board for the ESP32. Under the ESP32 is a the audio circuitry. I should have some extra boards to sell on Tindie soon. I will publish the source files soon.

The Firmware

The code is on Github. The port was relatively easy, but I had to rewrite a few libraries. They were designed so the main “setup” and “loop” parts did not change much. Currently the serial port based setup from the Mega version was not ported. This probably won’t be used. A wireless version is in the works.

Enclosure

The new enclosure is smaller. It prints quicker and is easier to fit in my backpack. The size is still big enough to hold comfortably while playing. The files will be uploaded to Thingiverse within the week.

Next Steps

  • Wireless control: I want a simple way to read the game statistics (average score, levels played, boos kills, etc) and tweak simple settings like audio volume and brightness. I think the easiest way is to make it a wifi access point with a simple web server. This eliminates having to write any client side apps and any smartphone or computer can hope on easily.
  • Levels: Make some way to edit or upload levels via wifi.
  • Multiplayer: I should be able to link multiple controllers. If I can think of a good dual player game idea, I might try to add that.
  • Python: It might be a fun challenge to write the game in Micro Python. This might open up the development to more people.

If you want to be notified of future blog posts, please subscribe.

 

Building a TWANG

Introduction

First…. Most of the credit must go to Robin Baumgarten and Critters for the inspiration and firmware. While I have hacked and tweaked the firmware a lot, the basic design is still all Critter’s. He did a great job.

A lot of people have asked me to help them build one, so this blog post is here to help them out. It is easy and fun to design and build your own parts and electronics. You can also either use my or Critters 3D printed parts.

The Electronics

The electronics are quite simple and only consist of a few basic pieces.

Arduino Mega – The firmware will not fit on an Arduino UNO, so you must use an Arduino Mega or anything using the the atmega2560 micro-controller. You can tpyically find a clone for less than $10.

MPU-6050 – This is a 3 axis MEMS accelerometer and gyroscope. The easiest way is to buy a GY-521 breakout board. You only need to use the VCC, GND, SCL and SDA pins. Note: My shield also has the INT pin, but that was for experimentation. You can find these breakout boards on Amazon for less than $5.

Speaker – You need a small standard speaker. The sound quality is not great, so don’t invest in anything expensive. I used an 8 Ohm speaker, but anything should probably work. The speaker is hooked directly to the Mega I/O, so you also need a 100 Ohm resistor in the speaker circuit. Typically a 1/10w to 1/4w resistor would be used. Note: This resistor is included on my shield. If you use my 3D printed design you will want a 40mm diameter with very little depth to it. Note: Do not connect directly to an amplifier. It is not designed for that.

LED Strip – The FastLED library that is used, supports a lot of types. I like the APA102C (Dotstar) type. I have also tested WS2812 (Neopixel) types. Most of the testing I did was on a 1 meter 144 LED APA102C strand and it looked great. The game gets difficult when there are less LEDs, so I would recommend at least 90. I have also tested with (2) 1 meter 144/m strips soldered together and a giant 5 meter 90 LED/M strip. They all look and work great.  The firmware supports up to 1000. Most longer strips are soldered smaller sections. It is easy to solder strips together like the image below. Be sure the 5V, Gnd, etc. are aligned the right way. I have some strips that are waterproof. That is not required, but does not hurt.

Note: Do not power the LED strip directly from the Arduino. Power it separately from a power supply. Note: My shield has an input for this. It will also power the Arduino.

Power Supply – Technically, you could need upwards of 40mA per LED. I bought a 10A supply and it has worked fine without getting hot up to 450 LEDs.

Life LEDs – The firmware supports remaining “life” LEDs. I prefer to use the main LED strip for this. It is fun to live within the limitations of the LED strip as the sole display. Using the strip also allows you to adjust the life count in firmware. The default is 3 lives per level, but I have boosted it to 5 for testing.  Note: My shield uses different I/O pins for the LED than the original TWANG firmware, so you need to check this if using them.

Wiring

The image below shows all the required connections to the Arduino Mega. My prototype used male header pins poked into the Arduino headers. It worked fine, but wires did often pop out when removing the cover.

The TWANG Shield

While hand wiring is very simple, I found it to be messy and I worried about failures. I made a basic shield to clean everything up. Here are the features of the shield.

  • LED Strip Terminal Block – It is very easy to hook up the strip. It works with both 3 and 4 wire strips. The power comes from the shield and no additional connections are required on the strip. Connections are clearly labeled. 3 wires LED strips do not use the CLK connection.
  • Accelerometer Terminal Block: This has clearly labeled connections using the same names that are on the MPU-6050 accelerometer module. Just hook them up 1 to 1.
  • Speaker Terminal Block: This also has 5V and Gnd if your hacking requires these connections. The 10 Ohm speaker resistor is mounted on the board.
  • Main 5V power entry connector: This powers the LED strip. It also powers the Arduino. It uses a diode so you can also power the Arduino via USB for programming.
  • Arduino UNO compatible: While the default firmware will not fit on an UNO, future compact version might be possible.
  • Life LEDs – My enclosure does not use them, but you could wire some in. The resistors are included, but not the LEDs. You could solder LEDS on the board or remotely locate them and solder wires to the PCB.

Shield Source Files

The 3D Printed Parts and other hardware

You need to 3D print a bunch of parts, a door spring, some hardware and a little hot glue.

Tindie Store

Typically I buy a small batch of PCBs for all my projects. If everything goes well I sell the rest on Tindie and often order more if they sell out.

  • Just the assembled shield. (coming soon)
  • A kit with all the custom parts
    • Assembled Shield
    • MPU-6050 wired and terminated with wire ferrules.
    • Speaker wired and terminated with wire ferrules
    • Door Spring

The Firmware

All of this is fully compatible with the original TWANG firmware. I forked the original and added a few changes. I would be happy to merge back to the original some time in future. The firmware relies on several libraries. Follow the instructions on GitHub pages to get those libraries.

Hacking the Firmware.

Hacking the firmware is quite easy. You should at least try editing some levels. More advanced hacking could improve the graphics and sounds.  Please give feedback if anyone has made any improvements.

At a minimum you have to set the number of LEDs and the LED strip type in the firmware before compiling.

Video

(coming soon) This thing looks so awesome in person, but is nearly impossible to video due to the crazy brightness of the LEDs. A friend is going to help me try to get a decent video.

In the mean time, take a look at Critter’s videos.


If you want to be notified of future blog posts, please subscribe.

TWANG Play Testing

 

I took my TWANG Clone to ORD Camp, NERP and the Hardware Happy Hour Meetup over the past week. It got a ton of play time.  I received a lot of feedback to work on.

Observations and Feedback.

It’s difficult to beat.  Only one person got all the way to the boss level and defeated it. Amazingly, it was Elan Lee. He loved the game and gave me some good ideas to work on.

Most people got killed in the second to last level. It has a lot of enemies and a conveyor that keeps pushing you back to the bottom. There is also a sneaky enemy spawner at the bottom that gets a lot of people.  It is a great level, so I don’t want to remove it. I have added a few more levels before it to practice before that.

The Lava Pools. The lava pools confused some people. I changed the pools to look more red, flickering and scary when they are on and less scary when off.  To me it looks more obvious now what to do.

The Sound. I love the chip tune style sound out of the Arduino, but it needs to be way louder. In a large crowd, you cannot hear it at all. I think it needs an amplifier or an option for an external speaker.

Boss Level: By design, the exit at the top of the boss level does not appear until all bosses are dead. People did not understand this and tried to exit out the top early, because the boss respawns below you after the first “kill”. That caused the players to try to leave the game without ending the level. If you exited the top in this mode, the player disappeared without a way back.  This is very annoying if you get all the way to this last level.  I fixed the code so you can’t goes past the second to last LED when the boss is still alive.

New Features: I asked several people for new ideas. I got some to work on, but already added one. The attack width is now adjustable. It will default to the old width, but you can change it per level.

More levels. A typical game lasts about about 1-2 minutes. I think a few more medium difficulty levels would help.

Scoring System: It would be cool to know how you did compared to others. It could display the score as a bar on the strip, with the max possible being the full length. You could then mark your level somehow by the strip. (Postit note flag, dry erase pen, etc)

Next Steps

  • Release all the source files.
    • Firmware: I have been hacking the code quite a bit.  I’ll release my changes after some clean up and testing.
    • STL files: I have been using odd sized speakers harvested from some cheap external speakers. When looking looking to buy some, it seems like 40mm diameter is a good standard size that is cheap and available. As soon as I get some and test them, I will release the files for this size.
    • Sell on Tindie. My shield makes wiring super easy, but is definitely not required.  I think I’ll sell everything, except for the Mega and LED strip. I’ll also just sell the assembled PCB by itself.
  • New Hardware:
    • Raspberry Pi Zero W: I have looked into several hardware options and this seems to be a good candidate. I think it will be a simple way to get good audio and connectivity. I have the accelerometer and LED strip working so far.  The audio will be an I2S amp chip that will be put on a shield. The (2) drawbacks are boot time (20-30 second) and you are probably limited to APA102C (dotstar) type LED strips. Edit: I got a good portion of the code on the Pi running. It runs fine, but I don’t like the requirement for a slow and controlled shutdown of the Pi. It would require a button and some sort of visual feedback.

 

 

TWANG Pi Zero Prototype


If you want to be notified of future blog posts, please subscribe.

TWANG Shield

While the my TWANG clone has been running great, I wanted to clean up the wiring, so I made a shield to plug into the Arduino. I previously used header connectors plugging into the Arduino. The connectors go to three different places and come from all over the Arduino , so there were a lot of connectors including some single pin ones. I was worried they might pop out or fail. I also had to externally power the LED strip and supply power via USB to the Arduino.

The shield takes care of all of this and groups all of the external connections by function on easy to connect and clearly labeled terminal blocks. Here are the features I have…

  • Single 5V Power Connector: This connector powers the LED strip via a very heavy trace on the PCB. It also powers the Arduino. The Arduino is powered through a Schottke diode. If you plug in the USB, the Arduino switches to be powered by the USB. This allows you to program and hack the firmware while the LED strip is powered.
  • Terminal Block Connections: The wires are grouped by peripheral (Accel, Speaker, LED Strip) and clearly labeled.
  • LED Strip Connections: This powers and controls the LED strip. I have tested it with 4 wire (APA102, Dotstar) and 3 wire (Neopixel) strips.
  • Speaker Connection: There is an integral 100 Ohm resistor that is required when you directly power the a speaker from an Arduino. The terminal block also has 5V and Gnd in case you want to add a simple amplifier. BTW: Driving the speaker directly from the Arduino is plenty loud in my opinion.
  • Shield Size: The shield will work on both an Arduino Mega sized board or an Arduino UNO sized board. The TWANG firmware requires the extra memory of the Mega, but a tiny, reduced feature, UNO version could probably be made.
  • Life LEDs: There are provisions for 3 LEDs that are typically used to show remaining lives. I have not been using those. I prefer to use the LED strip to show remaining lives. I like working with the restriction of a 1D LED strip display.

Prototype Assembly Notes: I did not have all of the correct parts for the build. I did not have a 100 Ohm SMD part, so I tacked on a through hole part. I did not have the right terminal blocks, so I cut one and only used 3 positions for the speaker. The correct parts will arrive soon.

Here are some more images.

 

Future Changes

  • I will probably get rid of the life LEDs.
  • I will add a large capacitor for sensitive LEDs, like Neopixels. Right now I just connect the cap to the terminal block.
  • I will probably sell the rest of this batch on my Tindie store in a week or two. I will probably sell assembled boards and full assemblies (less LED strip and Mega)
  • I will release of the documentation under an CC4.0-A-SA license.

If you want to be notified of future blog posts, please subscribe.

TWANG!

I have been a Patron of Robin Baumgarten for a while. He makes experimental hardware for games. His Line Wobbler one dimensional dungeon crawler is my favorite and I have always wanted to play it. It uses a door stop spring as the controller. An accelerometer in the knob allows it to work like a joystick and also detect the wobble used to attack the enemies.

Original Line Wobbler (Robin B.)

After seeing his playable Christmas tree version of the game, I had to make one for myself. I could not find any source files that he published, but I was able to find an open source clone called TWANG. The game is quite fun and surprisingly challenging.

Original Twang Version

Electronic Hardware

Here is a list of the electronics hardware used.

  • Arduino Mega.  The Mega is way overkill for the I/O requirements, but an UNO does not have enough memory.
  • MPU-6050 3 Axis Accel/Gyro Breakout Board. These are available for about $5 and have good library support for Arduino.
  • Small Speaker. I bought a pair of external PC speakers at Micro Center for $4 and pulled out some 2″ speakers. You need to use a 100 Ohm resistor on one of the wires.
  • RGB LED Strip: The default code is written for the APA102 type strips. The FastLED library used also supports the cheaper WS2812 (Neopixel) strips. I used a 144 LED 1 meter APA102 strip. The Clock and Data type strips can work faster and they typically have an overall brightness factor that gives them a more useful brightness range than Neopixels. The brightness of these strips is insane and you typically run them at about 1/2 brightness.
  • Life LEDs: You can use 3 individual LEDs to indicate the number of lives you have left. I decided to skip that. I preferred the simplicity of a signal display element. I added a game over animation to the game to make it more clear that you are dead, dead.

Printed Parts

I created my own 3D printed parts. I was having trouble with the TWANG Thingiverse files. They are OBJ files and the parts are grouped. Cura was not creating good prints. My speaker was not going to fit anyway.

  • Chassis: I made a heavy walled enclosure to give it a little weight and make it extra strong.
  • Cover: The cover is also very thick. The speaker mounts in a pocket and is attached with hot glue.
  • Spring Clamp. This holds the spring to the cover securely. I also added a little hot glue to prevent it from rotating.
  • Knob Base. This is very similar to the official TWANG version. It has a longer, threaded interface to grab the spring. This parts takes a lot of abuse.
  • Knob Top: Snaps on, but also gets a little hot glue.

The Firmware

The firmware is well written and pretty easy to follow. You need to download a lot of libraries. Some can be installed from the Arduino IDE and some must be downloaded manually. This is pretty well explained on the Github page.

Everything works on a 60 frames/second loop. This includes the display and the sound. I was able to tweak a few things easily and add a game over animation.

The levels are very easy to edit. You really don’t need to know how to program. I tweaked a few to make them easier for beginners.

Assembly

Build Spring Assembly

  • Solder wires to the accel module.
  • Slide the spring clamp over the spring.
  • Assemble the knob to the spring top.
  • Feed the wires through the knob base and spring.
  • Screw the module to the knob base.
  • Attach the knob top to the knob base.

 

 

Attach Spring to Cover (make sure spring stays vertical when attaching)

  • Adjust the metal spring base until the spring stands vertically.
  • Put a little bead of hot glue in recess on the cover
  • Feed the wires through and place the spring in the recess.
  •  Put a little hot glue around the spring where the clamp goes. Screw it down.

Attach Speaker to Cover

  • Blah
  • Attach some wires. Put a 100 Ohm, 1/4W inline on one of the wires.

Assemble Base

  • Install the Arduino Mega into the base with screws.
  • Connect all the wires per the graphic below. I wired the accel SCL/SDA at the left end, but you can also wire them to pins 20 & 21 at the right end.
  • Attach Cover

Usage

  • You need to power the LED strip with a separate 5V power supply. I used a 10A supply for my 144 LED strip.
  • You also need to power the Arduino. The easiest way is to do it via the USB port.  You could wire the power supply in the first step to the 5V on the Arduino, but be careful to never power from the power supply and the USB at the same time or something will likely break.
  • Note: I have been hooking up the LED power first. When I only power the Arduino, I see some flickering of LEDs.  That concerns me that it is drawing some power from the I/O pins.

Next Steps.

  • Make it Easier to Build: The wiring is a pain and probably not too durable. I used pins crimped into connectors that mated to the Arduino Mega. To make it easier I designed a little shield with screw clamps. It will also power the Arduino through a diode that will allow the USB to also be used. The speaker resistor is part of shield. It is also compatible with an Arduino UNO, so a pocket sized TWANG might be possible. That arrives next week. I will likely sell the extras on Tindie.
  • ESP32 Version: I would really like to try this. The sound and speed should be better and the ability to network with another player sounds cool. It is also smaller and cheaper.
  • Scoring System: Everyone want to compete.

Video

Here is a video of the Twang.

 



If you want to be notified of future blog posts, please subscribe.

Coasty Version 1.2

Here are some updates to Coasty – The Coaster Toaster,  the tiny laser cutter specifically designed to cut drink coasters.

New Traction Roller

I made the traction roller diameter a lot smaller and moved it behind the beam. A smaller roller has a lot of advantages. It allows the beam to be closer to the contact points of the rubber orings. This improves the usable work area, because you can get closer to the edge of the coaster. With a smaller diameter the coaster travels less per revolution. This increases the torque and resolution.

Smaller Chassis

The chassis is now about 16mm smaller in depth due to the smaller roller and new location. The depth of the machine is quite a bit smaller than the coaster.

Fan Guard and Carbon Filter

I added a fan cover on the back. This acts as a finger guard and also allows a few layers of carbon filter cloth to be used. Bulk carbon filter cloth for use in air purifiers can be purchased on Amazon very cheaply. It removes a good portion of the odor of the smoke.

Carbon Filter Cloth

Door Interlock Switch

There is now a switch that cuts all power to the laser when the door is opened. You can still run the machine to test the motors, homing etc, the the beam cannot turn on with the door open.

IR Coaster Detector

 

I was not happy with the coaster homing switch used on the first version. While it never failed, it did not appear to be very robust and it caused some drag on the coaster. I changed to a IR LED and photo diode. When the light from the LED hits the photo diode, it conducts to the +5V. When the coaster blocks the light, it is pulled down to ground. I used a pot on the pull down because it did not know what he exact value would be. It turns out the value needs to be about 40k. The only catch was the microcontroller input pin pull up resistor on the Nano could not not used because it is less than the 40k.  This required a slight hack to Grbl because Grbl is all or nothing on the pull ups for the limit switches.

I was not sure if ambient light changes might be a problem, like bright sunlight. The photo diode looks down and that appears to be good enough to avoid overhead light. I also have a mounting screw there in case I need to add a little shade/cover.

IR LED / Photo Diode Circuit

 

Bluetooth

I have been using Bluetooth on some other machines and really like it. Skipping USB cords and using a phone instead of a computer is great. I have found it to be very reliable. The real world bandwidth appears to be a little lower than 115200 USB. It has not been a problem, but I don’t do much gray scale engraving on this machine which needs higher bandwidth. Regardless, USB is still an option.

A standard HC-05 or HC-06 module plugs into a right angle connector.

Video

Here is a video of this version.


If you want to be notified of future blog posts, please subscribe.

The Polar Coaster – A Drink Coaster Drawing Machine

I designed this machine to draw custom, round drink coasters. I already have a laser cutter for square coasters and I wanted to try something unique for round coaster.

The Base

The base of the machine has two stacked 5mm bearings in the center for the bed to rotate on. There are (3) 3mm bearings on the bed perimeter that provide support and keep it level. They have little shafts that snap into the base.

The Bed

The bed is  a 156 tooth GT2 pulley. It has little springy fingers that grip the coaster when it is on the bed. The bed connects to the motor pulley with a closed loop belt.

The Radial Arm.

This is a belt driven, cantilevered arm that uses 6mm shafts and linear bearings. The belt is a cut pieces with the ends clamped at the carriage. It has a slotted mounting hole that lets the arm rotate. The pen must be adjustable to get to the exact center of the coaster or the drawing will be distorted. There is a limit switch on the top.  This is the only axis that needs to be homed. To setup the machine you home it and jog the pen until it is exactly over the center of the bed. You then set the work zero for X (Gcode: “G10 L20 P0 X0”). This only needs to be done once. If you use different types of pens, the center should be rechecked.

The Z Axis

The Z axis uses a micro servo and a cam to control the height of the pen. The firmware is setup to only have (2) Z positions, pen up and pen down. It uses 3mm rods and tiny little 3mm linear bearings.  There is a compression spring on one of the rods that applies a little pressure to the pen, and allows the pen to float a little on uneven coasters.

The Controller

I used my Grbl HAT controller. It is a bit overkill for this project but works perfectly.  It is attached to a Raspberry Pi in this photo, but I have not been using the Pi in this project yet. I just connect directly via USB.

Kinematics and Pre-Processin

See this blog post on how it was done. The pre-processor is written in C#, but it is rather simple and you could probably read the source file and convert if you cannot deal with C# on Windows.

Firmware

I use a modified version of Grbl 1.1f.  Grbl does not support servos, so I needed to hack that in.  I used the PWM that is normally used for the spindle speed to control the servo. I turned off the variable speed spindle option and streamlined the spindle functions to the bare minimum I thought Grbl needed.  I adjusted the PWM parameters for use with a servo and added pen_up() and pen_down() functions. I tried to put as much of the custom code into one file spindle_control.c. I had to add a few lines in stepper.c to look at the current machine Z height and apply the correct pen up/down function.

CAM

You can use anything to generate the gcode that works with Grbl. The pen will go up when the Z is above zero and down when it is below zero. Therefore, you want the Z movement as short as possible to speed up the drawing and not have the pen dwell on the material and bleed.  I make the depth of cut 1mm and the z clearance 3mm.

CAD Files.

The design was done using PTC CREO 3.0.  A STEP version of the design is linked at the end of the post.

Performance

It does a great job. Here a recent coaster. This was done from a rasterized bitmap image found online (searched: circular Celtic braid).

Here is a Fat Tire beer themed coaster.

Coasters are made to be super absorbent, so larger tipped felt pens tend to bleed a little too much. I like to sketch with Micron pens and the thinner ones really work well on this machine.

Build You Own?

The build is not difficult, but covers a lot of areas. You should know how to work with STEP files and compile firmware.

The design is open source with no commercial restrictions, so feel free to use any part of my work. I found most of the parts on Amazon and eBay. I bought the belt from Stock Drive Products. The polar motor pulley is 36 tooth and the arm pulley is 20 tooth.  Cutting the shafts requires an abrasive cutoff wheel.

Please post any questions in the comments section and I will try to address them.

Links

 

I sell on Tindie