Archive for the 'CNC' Category

Coasty Source Files

A lot of people have asked about building their own Coasty Laser Cutter. It takes a lot of work to get the files ready for release. I will release the source files in stages as they are ready so people can get started. Watch this post for updates. Subscribing to this blog or following me on Twitter (@buildlog) is a good way to keep up.

When everything is ready, I’ll probably also post on Thingiverse.

3D Printed Parts

Here are the STL files for the 3D printed parts. The parts are generally pretty easy to print. They require no support and can be printed in low resolution. I print at 0.28mm layer height. You need to watch out for warping on the chassis and front door. If the chassis warps it will stress the PCB and could damage some parts. The door needs to be flat in order to close properly.

I printed my parts in generic PLA. They printed fine, but if you have some crappier PLA or if you don’t have a heated bed, you should probably print with a brim. I would suggest printing the chassis first. If you can print that, the other parts are easier. I have some PETG on order to test. That supposedly warps less that PLA.

The holes used for the 8mm rods are designed to be a press fit. If the rods are hard to install, try cleaning the holes up a little by hand with a 5/16 or 8mm drill. The drive shaft bearing is also a tight fit. Try using a vise or clamp to press it into the chassis.

Zip File containing the STL files.

Mechanical BOM

 

Part DescriptionQtySupplierSupplier P/N
3mm Smooth Pulley (16T equiv dia.) 6mm Wide1
Bearing 3mm x 10mm x 4mm2Generic623-2RS
BEARING 5mm 16mm 5mm1Generic625-2RS
Bearing Shaft 8mm2
Butoon Head Screw M3 x 302
Button Head Screw M3 x 121
Button Head Screw M5 x 201
Coasty Chassis13D Print
Coasty Controller Assy1Buildlog.netCoasty Controller
Coasty Drive Shaft13D Printed Part
Coasty Final Assembly1---
Coasty Laser Carriage13D Printed Part
Coasty Laser Carriage Assy1User Assembly
Coasty X Motor Cover13D Printed Part
Dual Fan Cover13D Printer Part
Flat Head Screw M3 x 64
GT2 Belt 6mm Wide cut to 385mm1GenericGT2 6mm
Hex Nut M33
Laser Module 3.5W 450nm1EleksmakerLA03-3500
Linear Shaft Bearing 8mm Dual2GenericLM8LUU
NEMA14 Stepper Motor2Generic
StepperOnLine
14HS13-0804S
Nylock Locking Nut M22
Nylon Locking Nut M33
Pan Head Screw M2 x 122
Silicon Oring #9052McMaster Carr1283N428
Socket Head Screw M3 x 820
Socket Head Screw M3 x 162
Socket Head Screw M3 x 203
Timing Pulley GT2 18T 6mm Wide 5mm Bore1
Wiring Cover13D Printer Part
Coasty Window149mm x 76mmJ Tech PhotonicsRating: OD+4 @ 445nm

 

PCB Source Files

Coming Soon

Firmware

Coming Soon

Build Instructions

Assembly Drawing


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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.


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ESP32: Step Pulse Experiments with Timers

(Edit: Also check out my better “RMT” way to send the pulse)

I have been playing with the ESP32 microcontroller to see how well it would perform as a small scale CNC controller. The low cost and high performance as well as the built in Wifi and Bluetooth make it very attractive.

One of the challenges is step pulse timing. Most stepper drivers work with a direction signal and step signal. The step signals are a short pulse for each step. If they are too short, the driver will not detect them. If they are too long, it limits the rate at which you can send them.

You first set the direction signal high or low depending on the direction you want the motors to spin. You then send the step pulse. The direction signal has to be stable for a short period of time before the step signal is sent. The process is…

  1. Set direction
  2. Wait a bit (if it changed)
  3. Turn on the step pulse signal.
  4. Wait a bit
  5. Turn off the step pulse signal.

The timing is critical and varies by motor driver. Here is a typical spec.

Here are the specs for a few of the stepper drivers I regularly use.

 Allegro A4988TI DRV8825Toshiba TB6600
Direction Delay200ns650ns?
Step Pulse Delay1us1.9us2.2us

Test Firmware

Typically the firmware motion planner determines when to take a step, then sets an interrupt to occur at that time in the future. This allows the firmware to do other things like interacting with the user and planning future moves while it is waiting for the interrupt.

To simulate a stream of pulses, I created a timer interrupt that would case steps to occur at a constant 5kHz rate. That is onStepperDriverTimer() in the code.

In that interrupt service routine I first set the direction pin. Normally you only need to set it when the direction changes, but it will be easier to see this on a logic analyzer if I change it every time for this test. I then need to wait a little time before setting the step pulse pin. I could use another interrupt to do this, but the time is so short at about 750ns, that it is better to just waste a few cycles. In the CNC software I will only need to do this when the direction changes. That will be at the few beginning of the acceleration when the step rate is the slowest. I do this delay with a few NOP()s. The are “no operations”.

I then setup the the interrupt to end the pulse. That is onStepPulseOffTimer() in the code. I set the step pin after this because those instructions take clock cycles too. I can use those as part of my delay.

When that interrupt occurs, I turn off the step pulse signal. I also turn off the direction in this example. I am only doing it here so I can see that change on the logic analyzer. Normal CNC frmware would just leave it alone because there are typically thousands of steps before the direction is likely to change.

I wrote a program to simulate some CNC firmware so I could play with step pulse timing.

// create the hardware timers */
hw_timer_t * stepperDriverTimer = NULL;  // The main stepper driver timer
hw_timer_t * stepPulseOffTimer = NULL;  // This turns the step pulse off after xx uSeconds

// define the gpio pins
#define STEP_PIN 17
#define DIR_PIN 16

// the step pulse interrupt service routine. 
void IRAM_ATTR onStepperDriverTimer()
{
  // if ... the direction changed from last time (not in this demo)
  digitalWrite(DIR_PIN, HIGH);  // in actual CNC firmware this will go high or low
  for(uint8_t i=0; i<10; i++)
  {
    NOP();  // do nothing for one cycle
  }
  // end if

  // setup the pulse off timer
  timerWrite(stepPulseOffTimer, 0);
  timerAlarmWrite(stepPulseOffTimer, 22, false);  // the alarm point is found by looking at logic analyzer
  timerAlarmEnable(stepPulseOffTimer);  
  
  digitalWrite(STEP_PIN, HIGH); // put it after the timer setup to include the timeto do that
}


// 
void IRAM_ATTR onStepPulseOffTimer()
{
  digitalWrite(STEP_PIN, LOW); // end step pulse 
  digitalWrite(DIR_PIN, LOW); // only here for dem program CNC firmware would leave this until direction change
}


void setup() {  

 pinMode(DIR_PIN, OUTPUT);
 pinMode(STEP_PIN, OUTPUT);

    
 stepperDriverTimer = timerBegin(0, 4, true); // 80Mhz / 4  = 20Mhz// setup stepper timer interrupt ... this will simulate a flow of steps
 stepPulseOffTimer = timerBegin(1, 1, true); // 

 // attach the interrupts
 timerAttachInterrupt(stepperDriverTimer, &onStepperDriverTimer, true);// attach the interrupttimerAttachInterrupt(directionDelayTimer, &onDirectionDelayTimer, true);// attach the interrupt
 timerAttachInterrupt(stepPulseOffTimer, &onStepPulseOffTimer, true);// attach the interrupt
 
// setup the time for the 
 timerAlarmWrite(stepperDriverTimer, 4000, true);  // 20Mhz / 4000 = 5kHz rate ... this is the only one that auto repeats  
 timerAlarmEnable(stepperDriverTimer); 
 
}

void loop() {
  // no loop code required.:
  
}

Results

Here is a picture of my setup.

This is screen shot of what the logic analyzer captured. The upper line is the step signal and the lower line is the direction signal. The direction signal comes on first and then the step pulse signal comes on 0.75us later. The step pulse then lasts for about 2.5us before turning off.

Next Steps

  • I’ll go forward this method to see how well it works in actual CNC firmware.
  • I have been programming in the Arduino-ESP32 environment. This is an easy way to learn about the peripherals and do some quick tests. I may switch to the ESP-IDF  in the future.
  • I would like to investigate the RMT features of the ESP32. It is designed for Remote Controls, but I have heard it is quite flexible and might help with pulse generation.

 


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Using The midTbot Controller

The midTbot Controller is a controller for midTbot pen drawing machines. It is sold on my Tindie store. When fully populated, it has the following features.

  • (2) Stepper Motor Drivers for the X and Y axes with microstepping selector jumpers
  • Servo Connector for Pen Lift
  • Arduino Nano Controller
  • 5V power supply
  • (2) Homing switches
  • Bluetooth connector for HC-05 or HC-06 module.
  • Aux power connector for easy access to 5V and 12V power.

Power Supply

You will need a 12V DC power supply with at least 3A of power. The DC plug should be a coaxial 5.5mm x 2.1mm type with center positive. This type of plug is the most common type and should be pretty easy to find.

Microcontroller.

You should use an Arduino Nano compatible controller. The controller bootloader will need to be changed to the smaller Arduino UNO bootloader in order to fit the firmware. I have instructions on how to do this here. If you would like to buy one already modified, I sell them on my Tindie store. Be sure to install the controller in the correct orientation. The USB connector should face the edge of the controller as noted on the silkscreen of the controller PCB.

Stepper Drivers

You will need 2 stepper driver modules. I recommend ones based on the Allegro A4988 controller or the TI DRV 8825 controller. The drivers often come with heatsinks. The current will typically be set low enough that heatsinks are not needed.

You will need to set the microstepping level. I recommend using 1/8 microstepping. That gives a good balance of accuracy, smoothness and speed. You set this using the jumper blocks. Each stepper driver type has its own configuration. Here are the jumper setting for A4988 and DRV8825

Microstep ResolutionA4988 JumpersDRV 8825 Jumpers
FullNoneNone
1/2MS1MS1
1/4MS2MS2
1/8MS1 + MS2MS1+MS2
1/16MS1+MS2+MS3MS3
1/32Not AvailableMS1+MS2+MS3

Note the MS1, MS2 & MS3 labels next to the jumpers.

The orientation of the drivers is very important. You will break the drivers and likely other parts if you insert them wrong. Most drivers have the pins labeled and the the controller PCB has the corner pins labeled. Be sure the labels match. Here are the correct orientations for the A4988 and DRV8825.

You should set the stepper driver output current to the level required by your stepper motors. The midTbot does not need a lot of power. If you set the power too high, the motor could get hot and damage the 3D printed part it mounts to. You set the current by adjusting a potentiometer and reading a voltage. The drivers need to be powered when you do this. You can install them and power the board to do this. Do not connect the motors when adjusting the potentiometer. Each driver will have a small hole with exposed metal. This is the measurement point. The metal adjustment screw of the potentiometer is also a place you can measure. The reference voltage to current formulea are here.

DRV8825 Current = VREF * 2   (Example 0.4V = 0.8A current)

A4988 is a little more complicated because there are different versions. See this page.

Stepper motors:

The controller is designed for NEMA14 motors. Be sure to get 4 wire motors. Just about any size should work, but I prefer to use smaller ones to keep the size and weight down. You will need to attach connectors to them.  Trim the wires to the correct length so they reach the board connectors when installed. Wires colors should be installed as shown.

The wiring legend on the board that shows where to plug in the motors might not be right. It depends on the way the motor manufacturer wired the coils and which stepper drivers you use. You may need to swap them or rotate the connectors 180° if your axes are moving the wrong way. Here is a photo of how mine are wired. Try this first. Note the wire colors and which motor goes to which connector.

Bluetooth

You can add an HC-05 or HC-06 Bluetooth module. They have different connectors, but just match the pin names on both sides. You will need to setup the module to have a baud rate of 115200, N,8,1. I have detail on how to do that here (HC-05, HC-06).

 

 


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Bus Servo Draw Bot

I wanted to complete a start to finish project with the LX-16A bus servos to do a complete review of their viability for the type of mechatronics projects I do. The low price of the LewanSoul bus servos make them a competitive option over digital servos. I chose to do a remake of the Line-Us clone drawing machine because I would not need to spend too much design time and it would be a good 1:1 comparison with digital servos. Since the bus servos are quite a bit larger, I decided to scale up the machine by 1.5x.

Made My Own Brackets.

I started by buying one servo and it came with brackets. When I went to get more, I noticed the price was lower. I did not realize I was getting these without brackets. These are the brackets you get with the more complete kit.

I requested some 3D models from LewanSoul. They were only able to provide 2D DXF files, but they were easy to convert in Fusion 360. This allowed me to 3D print some brackets. It actually worked out quite well because I was able to thicken up the brackets and integrate some captive square nuts.

They mounted easily to the servos and were plenty strong for this project.

Servo Arms

I made two arms and one short cam for the Z. They were about 4mm thick and had a little pocket that slid over the standard round actuator. They screwed on with the screws that come with the servos. Before mounting anything I turned on the servos and moved them to the center of the range. This put the arms at a known angle.

Support Bracket and Base

The support bracket holds all three servos and there are 2 pockets on the bottom for some shaft bushings.

The base has two shafts pressed into it.

The shafts slide into the bushings and there is a spring to hold the parts together.  The spring prevents the pieces from separating and also provides a little extra pull down force in case the shafts bind a little. The cam provides about 6mm of lift.

Final Assembly

The servos are mounted to the support bracket.

The wires are connected to the servos. They just daisy chain from one servo to the next.

The remaining links are then connected.

Testing

Here is a video of the first run.

Results

I think these are a good alternative to digital servos. They are very strong, easy to mount and accurate. Depending on the design of the controller, using a simple UART might be easier than having multiple PWM signals or extra hardware. The servo’s size might be larger than some machines need but that comes with the higher power.

 

LewanSoul Lobot LX-16A Serial Servo Review

I stumbled upon these LewanSoul LX-16A Servos the other day on Amazon while searching for standard digital servos. These servos are digital serial bus servos. That means they use a serial protocol on a bus rather than a PWM signal. I have used bus servos before, but the $12 price got my attention. That competes well with plain old PWM servos.

Serial bus servos have some real advantages over standard PWM servos.

  • Wiring: The wiring can be a lot simpler because you can put all your servos on a single 3 wire bus. Each servo has 2 connectors to make daisy chaining easier.
  • Higher resolution: The resolution is typically higher. It depends on the way they sense position. These use a high accuracy potentiometer and list 0.24° as the resolution.
  • You can set the speed: You can set a destination and speed for each move.
  • Set the range: You can limit the range of the servo. This is great if the using the full range would crash a joint on your machine.
  • Continuous turn mode: There is a speed adjustable continuous rotation mode on these, but absolute distance moves cannot be done.
  • Motor On/Off: Turn the motor off for manual movement.
  • Feedback: The communication is bi-directional so you can query a servo for…
    • Position: If you manually move a servo, you get its position. This is great for recording “poses” or setting range limits.
    • Temperature: You can read the current temperature of the motors.

Compared to Robotis

I have used the Robotis Dynamixel XL320 servos before but these are a lot stronger and the XL-320 has a weird, plastic rivet, mounting systems that I am not fond of.

Here is a size comparison with a XL-320.

Specs

Spec LX-16A XL-320
Max. Torque 17 kg-cm 4 kg-cm
Resolution 0.24° 0.29°
Range 240° and Continuous Rotation 300° and Continuous Rotation
Speed 62 RPM 114 RPM
Weight 52g 16.7g

Usage

To use the servos you need to use one of their controllers. The most basic controller just converts a USB or TTL serial signal to their protocol. The controller is small and low cost ($10). You can send commands via a USB (Com Port) or via the TTL pins.

Setup Program.

They have a setup program.  The program is Windows only and I had to run it in Administrator mode to get it to work. This makes setting up the servos easy, but you could write your own program if you don’t want to use theirs.

TTL Control

They also provide some Arduino Sketches. They worked fine and are a good place to grab some code if you are writing your own program.  The sketches use the Arduino hardware TX and RX pins. That conflicts with uploading, so you need to disconnect the controller every time you upload. I edited the sketch to use SoftwareSerial on some other pins and that made playing with the code a lot easier.

First Impressions

I found the servos very easy to use and they appear to be strong and responsive. I think they will be a good option for my on my machines.

Next Steps

I want to test these in a real machine. I thought I might try to make a slightly larger version of my Line-Us clone. That would be a good comparison of accuracy. I might try one day build on it tomorrow.  I can probably get a machine designed and built in a day, but the controller programming would need more time.

 

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

 

 

 

Polar Pen Machine Kinematics

When you have a round work piece like a drink coaster, it makes sense to have a round work area.  A round work area works best with a polar coordinate system. A polar coordinate system uses an angle and a distance from a center point to define a point in 2D.

The problem is that most drawing and CAM programs work in Cartesian (X,Y,Z) coordinate systems. My machine controller firmware, Grbl, also works in normal linear X,Y, and Z. The process of converting one system to another uses Kinematics.

 

The Firmware

The firmware is side is actually quite easy. I defined the X axis as the distance in mm from the center (the radius). The Y axis will control the angle. The Y axis is setup so that millimeters will equal degrees. If I tell the Y to move 360mm, it will actually rotate the work area by 360°.  I could have used radians, but my brain works a lot slower in radians.

The machine will only need to home on the X axis. It needs to know where the exact center of the work area is. The starting angle does not matter because the coaster is a circle.

The conversion from X, Y to polar is probably won’t fit in into the firmware, so the X, Y conversion is done in a preprocessor software program. The X,Y gcode is output from normal CAM programs, then run through a conversion program.

The Conversion Program

The program reads the X,Y gcode, converts any X or Y coordinates into polar coordinates and outputs a new gcode file. The sender simply sends the new files.  The math is actually quite simple.

Typical Gcode sends line data by giving the end points of lines. You simply draw from one point to the next, unfortunately this creates a few problems with a non linear machine.

The basic non-linearity problem

If we were trying to draw the green square centered on the work area, the generated gcode would basically send the corner points. Each corner point has an equal radius to the center. Therefore, the pen will never change radius when going to the next point. This will result in a circle. We want the green square, but we get the red circle.

We need to calculate each point along the way to stay on the desired path. The preprocessor divides the line into tiny segments. Each segment has the same problem, but at a scale you won’t be able to see.

The Spiral Problem

If we are drawing a shape that crosses the 0° angle we don’t want the angle to spin the wrong way. If a point is at 350° and the next point is 10° (crosses over 0) we don’t want it to spin backwards from 350° to 10°. We want it to go to 370°.  It happens anywhere the angle difference between 2 points is greater than 180°. The program will choose the shortest direction even if that means going above 360° or below 0° degrees.

The Feed Rate Problem

Feed rate, in CNC terms, is the speed of the tool across the material. The CAM software is setting the feed rate as if this were a Cartesian machine. On this machine, if you were drawing a circle, you would simply move 360 units in Y. Without compensating feed rate, the pen would move across the work piece faster for larger diameter circles. I want to do some sort of compensation to help with this. The coasters are very absorbent, so the  lines look thicker if the speed is slower. A consistent speed will help the quality of the work.

Since the lines are all very short, the easiest way to compensate for feed rate is to use the current radius. With a simple circle, Grbl thinks the machine moved 360mm. The real distance is easy to to calculate from the perimeter of that circle.

We can compare it to the 360mm (full circle) and apply the ratio to the desired feed rate from the CAM program.

polarFeedrate = cartesianFeedrate * 360 / (2 * pi * radius)

 

Video

Here is a video of it. The machine is rerunning a file to see the repeatability.

Next Steps.

I would like to automate the preprocessor.  I think a Raspberry pi, might be an easy way to do this.  It would sit between the sender and the controller.

 

 

 

Coasty Update

Here is a quick update on Coasty. Several people have asked if I am releasing the source files or selling a kit. I am adjusting the design to make that more viable.  The original version was made with parts I had laying about and not necessarily the best design choices for an open source project.

X Axis.

Originally I used an TR8-8 ACME thread lead screw. It was mounted to the motor by drilling a hole in the lead screw and epoxying it to the motor shaft. This worked well, but you needed a lathe to drill the hole and a special low backlash nut. The axis was also a little loud with and all metal design.

I changed to use a GT2 open belt cut to length.  Belts and pulley are really easy to get and don’t cost too much.

Electronics

Need to shorten some wires after testing.

There were some issues with the EleksMaker electronics that I did not like. The laser circuit did not appear to have a pull down on the signal and it tended to fire if the Arduino was not pulling it low. This would happen during reboot and other scary times. The wiring was also quite a pain. There were no connectors for the limit switches so you had to directly solder to the Arduino Nano.

I changed to use a custom PCB that is the entire rear panel. This contains all of the circuits including the limit switches. Building a Coasty was a little like building a ship in a bottle. Now the bottle has no bottom and there are less parts inside.

Front Door.

The front door now has a window. This makes the machine more fun to watch and no glasses are required.

Next Steps.

I have one build and am testing it for a while. If all goes well, I will release the source files and consider a kit.

 

PSoC 5 Daughter Card for XCC

I finished a PSoC 5 daughter card design for X-Controller-Controller project.  10 boards should arrive in about a week. This will clean up all the wiring from the breadboard testing I have been doing. My goal is to have a clean development platform for me and possibly others to work with.

The design has the following features.

  • Mounts CY8CKIT-059 dev board directly
  • Mates directly to the X-controller-Controller
  • Independent control of 4 axes.
  • Connector for X-Controller button panel
  • Connector for  X-Controller power supply PCB
  • Connector for a Serial LCD panel (Itead Studio Nextion style)
  • PSoC controlled stepper motor current.
  • PCoC controlled idle current.

Here is an image of the CYC8CKIT-059 development board.  The CPU is a PSoC 5LP.  The price is only about $10.  It comes with a built in programmer, debugger, and USB/UART. This can be snapped off.  To fit into the X-Controller, I snap off the programmer and mount it in another location.  The connections are made on the PCB.  I plan to use stackable headers so all of the pins are still easily accessible.

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