12. Mechanical and machine design

Mechanical Design (part 1 of 2)

Group Assignment

  1. Design a machine that includes mechanism + actuation + automation
  2. Build the mechanical parts and operate it manually.
  3. Document the group project

Individual assignment

  1. Document your individual contribution.

Machine Design (part 2 of 2)

Group Assignment

  1. Actuate and automate your machine.
  2. Document the group project

Individual assignment

  1. Document your individual contribution.

Group videos

Dan Meyer: Foam Crawler

Alan Han: Urumbu Crawler

Kyle-Pierre: Bend Crawler

Design

FoamCrawler CNC I designed the Foam Crawler machine in Onshape. It has two X Axis rollers covered in grip tape It has two Y Axis drive rollers no platen at all. It has two un-driven upper rollers. The Z axis is 8mm Metric Acme Lead Screw, X Axis is belt drive on makerslide. These 3 different drive types will be interesting to actuate manually by hand.

I went through a few iterations of the Y roller drive. The first was PVC pipe spiral wrapped with emery cloth glued onto PVC pipe.

Manual Operation


Here I am holding the parts in place to run each axis by hand.

When run by hand with a piece of foam this setup has a few issues.

  1. the foam would work it’s way along the x axis due to the spiral and the PVC pipes were hard to buy without bending and roundness defects, leading to a kind of clapping onto and off of the foam sheet while being driven.
  2. The hand operation also revealed that accelerating and decelerating the rollers took a surprising amount of force.
  3. The M8 bolts were also loose in the bearings leading to slop.

Other uses

Kyle-Pierre Nfr would like to modify the foam crawler to index acrylic sheets over a heating element. Once the acrylic is soft paddles would bend the acrylic to a specific angle and let the acrylic cool. Then the acrylic would advance and the process would repeat. One use for this process would be for machine covers. Even with this modification the Foam Crawler could be used as originally designed

727 Glider Cutting


I cut some 727 gliders on the foam crawler to test it out.

Individual Assignment

Actuate and automate your machine

GRBL gSheild Setup

I have a lot of Synthetos gShield CNC controllers in stock, so that’s what I used to actuate the Foam Crawler. The instructions for connecting the gShield I used are here: Using grblShield

I compiled, flashed, programmed and setup the gShield cnc control using grbl.

Installing and getting USB to work with the Arduino IDE on Linux is not well documented. Here is a good post to help: Arduino IDE on Linux Mint

The GRBL wiki has good instructions on how to compile and install GRBL: Grbl wiki!

Universal Gcode Sender(UGS)

To send gcode I decided to use Universal Gcode Sender(UGS) software in the “platform” flavor. The download for linux platform UGS was located at: https://github.com/winder/Universal-G-Code-Sender.

After wiring up my 24VDC power supply, I plugged a USB cable between my computer and the Arduino UNO with gShield.

I fired up UGS and clicked the Port: to select the port the Arduino UNO was on.

Then I clicked the “Machine” and then “Connect”… and GRBL initialized and talked back! YES!

It’s Alive!

I then executed some jog moves, they worked moving my X and Y axis along with lighting up the green lights on the gSheild stepper outputs! Although the movements were very weak. I needed to set my stepper driver currents.

Setting Stepper Currents

I used the procedure on the synthetos/grblShield wiki Setting Motor Current to intially set the stepper motor currents.

Later I will verify the current settings with Vref measurements. This is a good guide on that process: Setting the stepper motor current limit from this page “The gShield (version 5) uses a 0.1 ohm current sense resistor so the formula is Vref = 0.8 * I.

The maximum current the driver chip can deliver with appropriate cooling is 2.5 amps. To use this current value you would set the Vref voltage at (0.8 * 2.5 amps) = 2 volts. This is the theoretical current limit.”

Note: the gSheild stepper driver are limited to 2.5 amps

Stepper Multiplier Target Amps Vref
NEMA 28 X&Y Axes KL23H251-28-4A 0.8 2.5 A 2.0 V
NEMA 17 Z Axis SM42HT47-1684B 0.8 1.68 A 1.3 V

Steps per mm

Next I used the GRBL settings calculator to get the correct distance movements. I also found the Norwegian Creations Tutorial: Calibrating Stepper Motor Machines with Belts and Pulleys useful for the roller drive calculations. Grbl v1.1 commands can be found here: (https://github.com/gnea/grbl/wiki/Grbl-v1.1-Commands) I also found the FABLAB León LE-CAR-BIL MACHINE documentation useful.

My steps per mm calculations:

X axis

Steps/rev: 360 deg / Step Angle 1.8Deg = 200
Microsteps: 4 micro steps per step Belt Pitch: 3mm Pulley Teeth: 20

srev is the number of steps per revolution for the motor fm is the microstepping factor (1, 2, 4, 8 etc.) p is the pitch Nt is the number of teeth on the pulley attached to the motor shaft.

srev * fm / p * Nt
200 * 4 / 3 * 20 =
800 / 60 =
13.333 steps per mm

Y axis

Belt Pitch: 3mm
Steps/rev: 360 deg / Step Angle 1.8Deg = 200
Roller Diameter: 42.9mm
Microsteps: 4 micro steps per step

srev is the number of steps per revolution for the motor
Nf is the number of teeth on the final (passive) pulley
fm is the microstepping factor (1, 2, 4, 8 etc.)
Nm is the number of teeth on the motor pulley
Dr is the diameter of the roller

srev * Nf * fm / Nm * piDr
200 * 20 * 4 / 20 * (3.14159 * 42.9) =
16000 / 2695.48422 =
5.936 steps per mm

However, as expected, the variable slip vs grip nature of the grip taped Y Axis rollers needed steps per mm adjustment.

Using the helpful info GRBL Steps Per mm – How to Fine Tune Your Settings I re-calibrated.

On a 441.7 mm move the actual cut length was 444.5

Updated Steps/mm = (Current Steps/mm) x (Commanded Travel) / Actual Cut Length

5.936 * 441.7 / 444.5 = 5.899

5.899 Adjusted steps per mm

Z axis

8mm Metric Acme Lead Screw This Tr8*8-2p(4 starts) trapezoidal Lead Screw results in a pitch of 8mm. Pitch of a lead screw is the distance traveled with one revolution. In this case one revolution results in 8mm movement. If you are not sure of a threaded rod pitch simply put a nut on it and rotate it 1 revolution and measure the distance moved.

Z motor (steps/rev): 360 deg / Step Angle 1.8Deg = 200
Z Microsteps: 8 micro steps per step
Z threaded rod pitch (mm): 8
Pulley Teeth: 1 (direct drive)

srev is the number of steps per revolution for the motor fm is the microstepping factor (1, 2, 4, 8 etc.) p is the pitch Nt is the number of teeth on the pulley attached to the motor shaft. For direct drive use 1.

srev * fm / p * Nt 200 * 2 / 8 * 1 = 400 / 8 =
50 steps per mm

Axis Steps per mm Setting Command
X 13.333 $100=13.333
Y 5.899 $101=5.899
Z 50 $102=50
Inverting Axes

The Z axis was inverted, So I issued the following command to Invert Z:
$3=4
Carefully read the documentation at: (https://github.com/gnea/grbl/wiki/Grbl-v1.1-Configuration#3–direction-port-invert-mask) and you will be able to understand how the code above works.

Max Feed Rates

Jogging the machine was painfully slow. So I updated the following Max rate, mm/min
X $110=8000
Y $111=8000
Z $112=4000

Acceleration

Acceleration could be increased as well
X $120=3000
Y $121=3000
Z $122=200

Dan’s Foam Crawler Video

Above is a video of the Foam Crawler CNC Machine being actuated and run. In the video the Foam Crawler is cutting a simple example to demonstrate its basic capabilities. See my main Foam Crawler page for further work on how the Foam Crawler was designed, fabricated and built.

CAD Files

FoamCrawler CNC Onshape CAD Assembly Files

Exploded View & BOM


Above: Isometric View of Foam Crawler Assembly

PDF Exploded View BOM
Click the image above to view or download a PDF Exploded View & BOM to help assemble your Foam Crawler core. Foam Crawler Core Exploded View & BOM

BOM Chart

Item Quantity Name Part number Description Process Material Vendor Cost Per Multi Cost Link
9 1 Z Drive Mount 17 3D Printed PLA You 0.22 0.22
11 3 Stepper Spacer 3D Printed PLA You 0.1 0.30
14 1 XDriveMount 3D Printed PLA You 0.5 0.50
19 1 Idler Bracket Mirror 3D Printed PLA You 0.1 0.10
23 8 RollerEndCap 3D Printed PLA You 0.2 1.60
27 4 Roller Cradle 3D Printed PLA You 0.5 2.00
32 2 Clamp XBelt 3D Printed PLA You 0.1 0.20
33 1 Cover Left Lower 3D Printed PLA You 5 5.00
34 1 Cover 24V 3D Printed PLA You 2 2.00
35 1 Cover 48V 3D Printed PLA You 2 2.00
39 1 Frame Left Window 3D Printed PLA You 0.1 0.10
40 1 Front Frame Electronics 3D Printed Acrylic You 0 0.00
41 1 Spindle Clamp 3D Printed PLA You 0.2 0.20
43 3 Vent 3D Printed PLA You 0.2 0.60
49 1 Plug Y Drive 3D Printed PLA You 0.2 0.20
50 1 zip tie mount makerslide 3D Printed PLA You 0.1 0.10
4 1 Spindle B01F86IKXO DC Spindle 24vdc preferred As is Copper Inventables 29.88 29.88 https://www.amazon.com/spindle-12-48v-Spindle-Engraving-Machine/dp/B01F86IKXO
5 2 Nema 23 Stepper Motor 518 Nema 23 Stepper Motor As is Carbon Steel Inventables 27.99 55.98 https://openbuildspartstore.com/nema-23-stepper-motor/
8 1 Nema 17 Stepper Motor 623 Nema 17 Stepper Motor As is Carbon Steel Inventables 17.99 17.99 https://openbuildspartstore.com/nema-17-stepper-motor/
13 1 IdlerPlate 30162-01 Idler Pulley Bracket As is Aluminum ## BOM Inventables 5 5.00 https://www.inventables.com/technologies/idler-pulley-bracket
2 1 MakerSlideX 25142-14 MakerSlide Chop Saw Cut Aluminum Inventables 13.49 13.49 https://www.inventables.com/technologies/makerslide#25142-14
15 2 40x20 Extrusion 26047-02 20 x 20 Extrusion Chop Saw Cut Aluminum MSI 9 18.00 https://www.inventables.com/technologies/aluminum-extrusion-20mm-x-20mm-clear#26047-02
1 2 SidePlate 30364-01 SidePlate CNC Milled HDPE (High-Density Polyethylene) Inventables 7.17 14.34 https://www.inventables.com/technologies/two-color-hdpe-white-on-green#30364-01
3 1 SpindleMount 8492K674 CNC Milled Acetal (Delrin) McMaster Carr 9.17 9.17 https://www.mcmaster.com/8492K674
16 6 Flanged Ball Bearing 688ZZ 688ZZ Flanged Bearing 8x16x5mm Hardware Hardened Alloy Steel Amazon 1.2 7.20 https://www.amazon.com/uxcell-Bearing-8x16x5mm-Shielded-Bearings/dp/B07Z3F68H4
28 12 M8 Washer 93475A270 18-8 Stainless Steel Washer for M8 Screw Size, 8.4 mm ID, 16 mm OD Hardware Steel Grade 2 McMaster Carr 0.1095 1.31 https://www.mcmaster.com/93475A270/
36 1 Back Plane Electronics Laser Cut Acrylic You 0 0.00
37 1 Bottom Plate Electronics Laser Cut Acrylic You 0 0.00
38 1 Electronics Window Laser Cut Acrylic You 0 0.00
42 1 Top Plate Electronics Laser Cut Acrylic You 0 0.00
6 3 GT3 Timing Pulley 20 Tooth 9mm Belt 8mm Clamp Bore 2130 3GT (GT2-3M) Timing Pulley - 20 Tooth - 9mm Belt - 8mm Clamp Bore Purchased Aluminum - 1060 OpenBuilds / SDP/SI 9.99 29.97 https://openbuildspartstore.com/3gt-gt2-3m-timing-pulley-20-tooth-9mm-belt-8mm-clamp-bore/
7 1 8mm Acme Nut Block 740-Set Nut Block for 8mm Metric Acme Lead Screw Purchased Acetal (Delrin) OpenBuilds 7.49 7.49 https://openbuildspartstore.com/nut-block-for-8mm-metric-acme-lead-screw/
10 2 BeltLoop 2120 3GT (GT2-3M) 9mm Timing Belt - Closed Loop Purchased Fluoroelastomer (FKM) OpenBuilds 8.99 17.98 https://openbuildspartstore.com/3gt-gt2-3m-9mm-timing-belt-closed-loop/
12 2 GT3 Timing Pulley 20 Tooth 712 3GT (GT2-3M) Timing Pulley - 20 Tooth - .250” Bore - 9mm Belt Purchased Aluminum - 1060 OpenBuilds 7.99 15.98 https://openbuildspartstore.com/3gt-gt2-3m-timing-pulley-20-tooth-250-bore-9mm-belt/
17 1 Coupler 155 1/4” x 8mm Flexible Coupling Purchased Aluminum OpenBuilds 6.99 6.99 https://openbuildspartstore.com/1-4-x-8mm-flexible-coupling/
18 1 8mm Lead Screw 25-LP 8mm Metric Acme Lead Screw Purchased Hardened Alloy Steel OpenBuilds 10.99 10.99 https://openbuildspartstore.com/8mm-metric-acme-lead-screw/
20 2 Pulley 550 Smooth Idler Pulley Wheel Purchased Acetal (Delrin) OpenBuilds 5.99 11.98 https://openbuildspartstore.com/smooth-idler-pulley-kit/
21 1 24VDCPowerSupply LRS-350-24 24VDC Single Output Switching Power Supply, can be used for stepper motors and 24VDC spindles Purchased - None - MEAN WELL/Amazon 38 38.00 https://www.amazon.com/MEAN-WELL-LRS-350-24-Switching-Printer/dp/B07SQLJG5L
22 1 48VDCPowerSupply SE-450-48 Not used unless 48 VDC Spindle is used Purchased - None - MEAN WELL/Amazon 75 75.00 https://www.amazon.com/MEAN-WELL-SE-450-48-Supply-Single/dp/B005T7NDXU
24 2 8mm Shaft Long 4634T34 5/16 in. x 36 in. Zinc-Plated Round Rod Purchased Stainless Steel 18-8 McMaster Carr 2 4.00 https://www.mcmaster.com/4634T34
25 2 Lower Roller #669669 1-1/4 in. Aluminum Rigid Conduit Purchased Aluminum - 6061 Home Depot 0 0.00
26 2 8mm Shaft Mid 4634T34 5/16 in. x 36 in. Zinc-Plated Round Rod Purchased Aluminum - 6061 McMaster Carr 2 4.00 https://www.mcmaster.com/4634T34
29 4 8mm Shaft Short 4634T34 5/16 in. x 36 in. Zinc-Plated Round Rod Purchased Aluminum - 6061 McMaster Carr 2 8.00 https://www.mcmaster.com/4634T34
30 2 Upper Roller #669669 1-1/4 in. Aluminum Rigid Conduit Purchased Aluminum - 6061 Home Depot 30.2 60.40 https://www.homedepot.com/p/1-1-4-in-Aluminum-Rigid-Conduit-732303/100192934
31 1 X Belt 470 3 feet of GT2-2M Timing Belt Purchased Fluoroelastomer (FKM) OpenBuilds 7.47 7.47 https://openbuildspartstore.com/gt2-2m-timing-belt-by-the-foot/
44 8 Spring Loaded Tee Nut Purchased Aluminum - 1060 Inventables 1.049 8.39 https://www.inventables.com/technologies/post-assembly-t-slot-nuts#26016-01
45 4 Joining Strip Plate 3 Hole 646 3 Hole Joining Strip Plate Purchased Aluminum - 1060 OpenBuilds 1.99 7.96 https://openbuildspartstore.com/3-hole-joining-strip-plate/
46 1 IEC Power Entry Module JR-101-1F Un-Filtered IEC Power Entry Module, IEC C14, 6.3 A, 250 VAC, 1-Pole Fuse Holder Purchased - None - Newark 2.56 2.56 https://www.newark.com/multicomp-pro/jr-101-1f/fused-iec-power-connector-plug/dp/38K3208
47 1 USB - Type B - Female - Panel Mount B071P2BGK5 USB 2.0 B Female Panel Mount to 90 Degree USB B Male 0.5m length. Purchased - None - Amazon 8 8.00 https://smile.amazon.com/gp/product/B071P2BGK5/ or https://www.aliexpress.com/item/32764330008.html 5 pcs
48 1 L Bracket Double 485 L Bracket, Double Purchased Aluminum - 1060 OpenBuilds 1.49 1.49 https://openbuildspartstore.com/l-bracket/
51 1 SWITCH ROCKER SPST 16A 125V PRASA1-16F-BB0BW Rocker Switch, On-Off, SPST, Panel Mount, Black, PRA Series Purchased - None - Newark 0.503 0.50 https://www.newark.com/alcoswitch-te-connectivity/prasa1-16f-bb0bw/switch-operation-on-off/dp/14J6535?st=prasa1-16f-bb0bw
52 1 24VDC Fan 2410SB-05W-B40-B00 DC Axial Fan, 24 V, Square, 60 mm, 25 mm, Ball Bearing, 19.8 CFM Purchased - None - Newark 9.4 9.40 https://www.newark.com/nmb-technologies/2410sb-05w-b40-b00/fan-axial-60mm-x-60mm-x-25mm-24vdc/dp/55T9978
53 1 Socket button head screw M8x1.25 x 35 92095A292 Socket button head screw M8x1.25 x 35 Stainless Steel 18-8 Purchased Stainless Steel 18-8 McMaster Carr 0.959 0.96 https://www.mcmaster.com/92095A292
54 16 Socket button head screw M5x0.8 x 8 92095A292 Socket button head screw M5x0.8 x 8 Stainless Steel 18-8 Black Oxide Purchased Stainless Steel 18-8 McMaster Carr 0.1633 2.61 https://www.mcmaster.com/92095A207
55 8 Socket button head screw M5x0.8 x 12 92095A210 Purchased Stainless Steel 18-8 McMaster Carr 0.202 1.62 https://www.mcmaster.com/92095A210
56 4 Socket button head screw M5x0.8 x 14 94500A298 Purchased Stainless Steel 18-8 McMaster Carr 0.1406 0.56 https://www.mcmaster.com/94500A298
57 3 Socket button head screw M5x0.8 x 16 92095A212 Socket button head screw M5x0.8 x 16 Stainless Steel 18-8 Purchased Stainless Steel 18-8 McMaster Carr 0.2264 0.68 https://www.mcmaster.com/92095A212
58 16 Socket button head screw M5x0.8 x 25 94500A299 Socket button head screw M5x0.8 x 25 Stainless Steel 18-8 Purchased Stainless Steel 18-8 McMaster Carr 0.185 2.96 https://www.mcmaster.com/94500A299
59 1 Socket button head screw M5x0.8 x 35 97654A222 Purchased Stainless Steel 18-8 McMaster Carr 0.176 0.18 https://www.mcmaster.com/97654A222
60 4 Hex socket head cap screw M5x0.80 x 16 91292A126 Hex socket head cap screw M5x0.80 x 16 Stainless Steel Purchased Stainless Steel McMaster Carr 0.1363 0.55 https://www.mcmaster.com/91292A126
61 3 Hex socket head cap screw M5x0.80 x 35 x 22 91292A193 Purchased Stainless Steel McMaster Carr 0.2928 0.88 https://www.mcmaster.com/91292A193
62 4 Socket button head screw M4x0.7 x 8 92095A189 Socket button head screw M4x0.7 x 8 Stainless Steel 18-8 Black Oxide Purchased Stainless Steel 18-8 McMaster Carr 0.0919 0.37 https://www.mcmaster.com/92095A189/
63 10 Socket button head screw M4x0.7 x 10 92095A190 Socket button head screw M4x0.7 x 10 Stainless Steel 18-8 Purchased Stainless Steel 18-8 McMaster Carr 0.0859 0.86 https://www.mcmaster.com/92095A190/
64 4 Socket button head screw M3x0.5 x 10 92095A182 Socket button head screw M3x0.5 x 10 Stainless Steel 18-8 Purchased Stainless Steel 18-8 McMaster Carr 0.0796 0.32 https://www.mcmaster.com/92095A182/
65 2 Hex socket countersunk head screw M3x0.5 x 8 92125A128 Hex socket countersunk head screw M3x0.5 x 8 Stainless Steel Black Oxide Purchased Stainless Steel McMaster Carr 0.0565 0.11 https://www.mcmaster.com/92125A128/
66 4 Hex socket countersunk head screw M3x0.5 x 10 92125A130 Hex socket countersunk head screw M3x0.5 x 10 Stainless Steel Black Oxide Purchased Stainless Steel McMaster Carr 0.0695 0.28 https://www.mcmaster.com/92125A130/
67 1 Hex nut grade A & B M8x1.25 93625A300 Hex nut grade A & B M8x1.25 Stainless Steel Purchased Stainless Steel McMaster Carr 0.2326 0.23 https://www.mcmaster.com/93625A300/
68 13 Hex nut grade A & B M5x0.8 93625A200 Hex nut grade A & B M5x0.8 Stainless Steel Purchased Stainless Steel McMaster Carr 0.0886 1.15 https://www.mcmaster.com/93625A200/
69 4 Hex nut style 1 grade A & B M3x0.5 93625A100 Hex nut style 1 grade A & B M3x0.5 Stainless Steel Purchased Stainless Steel McMaster Carr 0.0694 0.28 https://www.mcmaster.com/93625A100/
70 1 Plain washer large grade A M5 91116A140 Plain washer large grade A M5 Stainless Steel Purchased Stainless Steel McMaster Carr 0.1296 0.13 https://www.mcmaster.com/91116A140/
71 1 Plain washer normal grade A M5 98689A114 Plain washer normal grade A M5 Stainless Steel Purchased Stainless Steel McMaster Carr 0.0371 0.04 https://www.mcmaster.com/98689A114/
Total $538.79

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