Jake Read committed Sep 30, 2019 1 ``````# The Displacement Exercise (DEX) `````` Jake Read committed Aug 28, 2018 2 `````` `````` Jake Read committed Oct 18, 2019 3 ``````DEX is a small materials testing machine that should be capable of running tensile and compressive tests at up to 600N of force. `````` Jake Read committed May 10, 2019 4 `````` `````` Jake Read committed Oct 17, 2019 5 6 7 ``````| | | | --- | --- | | ![dex](images/2019-10-17_dex-01.jpg) | ![dex](images/2019-10-17_dex-03.jpg) | `````` Jake Read committed May 10, 2019 8 `````` `````` Jake Read committed Oct 18, 2019 9 ``````## Operating Principle `````` Jake Read committed Sep 30, 2019 10 `````` `````` Jake Read committed Oct 18, 2019 11 ``````A [stress - strain plot](https://en.wikipedia.org/wiki/Stress%E2%80%93strain_curve) is a very useful piece of information when characterizing materials. `````` Jake Read committed Sep 30, 2019 12 `````` `````` Jake Read committed Oct 18, 2019 13 ``````![ss curve](images/stress-strain.jpg) `````` Jake Read committed Oct 17, 2019 14 `````` `````` Jake Read committed Oct 18, 2019 15 ``````To generate these curves, the DEX slowly pulls samples (normally some 'dogbone' shape [below](#testing-notes)) apart, while measuring the amount that it stretches (~ the strain), and the amount of force it exerts as it is stretched (~ the stress). These types of machine are common in industry, commonly referred to by their leading brand name 'Instron', or as 'Universal Testing Machines'. `````` Jake Read committed Sep 30, 2019 16 `````` `````` Jake Read committed Oct 18, 2019 17 ``````## Hardware `````` Jake Read committed Sep 30, 2019 18 `````` `````` Jake Read committed Oct 18, 2019 19 ``````The DEX is an open-source piece of materials testing equipment. The machine can be manufactured by anyone with access to a laser cutter with at least a 24x12" bed, and nearly any FDM 3D Printer. A bill of materials of purchased parts required to complete the machine is below, totaling some ~ \$500 USD. `````` Jake Read committed Sep 30, 2019 20 `````` `````` Jake Read committed Oct 17, 2019 21 22 ``````The machine is made largely from [laser cut](https://hackaday.com/2015/09/03/how-to-build-anything-using-delrin-and-a-laser-cutter/) [delrin](https://hackaday.com/2015/09/22/drawbacks-of-lased-delrin-and-how-to-slip-around-them/) and 3D printed (commodity FDM) parts. `````` Jake Read committed Oct 18, 2019 23 24 ``````More detailed documentation will follow. `````` Jake Read committed Oct 17, 2019 25 ``````### CAD `````` Jake Read committed Oct 08, 2019 26 `````` `````` Jake Read committed Oct 18, 2019 27 28 ``````CAD for the machine is available in this Repo, [under `cad/fusion`](https://gitlab.cba.mit.edu/jakeread/displacementexercise/tree/master/cad/fusion) - the `.f3z` file is a Fusion 360 parametric model of the machine. To source parts, consult the BOM below. `````` Jake Read committed Oct 17, 2019 29 ``````![dex](images/2019-09-27_DEX-CAD.png) `````` Jake Read committed May 10, 2019 30 `````` `````` Jake Read committed Sep 26, 2019 31 ``````### BOM `````` Jake Read committed May 10, 2019 32 `````` `````` Jake Read committed Oct 06, 2019 33 34 35 ``````Part numbers are from [McMaster Carr](http://mcmaster.com) unless otherwise linked. | Part | Spec | Count | Notes | PN / Link | Cost / Per | `````` Jake Read committed Sep 26, 2019 36 ``````| --- | --- | ---: | --- | ---: | ---: | `````` Jake Read committed Oct 06, 2019 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 ``````| Delrin (Acetal) Cast Sheet | 24x12", 0.25" Thick | 2 | Fits on 24x18" w/ no mistakes | 8573K35 | \$50.49 / 1 | | PLA 'Tough' | | ~ 300g | Many 3DP Mechanical Bits | [Matter Hackers M6E9T65K](https://www.matterhackers.com/store/l/light-blue-pro-series-tough-pla-filament-175mm-1kg/sk/M6E9T65K) | \$52.00 / 1kg | | 625ZZ Bearings | 5x16x5 | 24 | - | [VXB 625ZZ](https://www.vxb.com/20-625ZZ-Shielded-5mm-Bore-Diameter-Miniature-p/625zz20.htm) | \$24.95 / 20 | | Bearing Shims | 5x10x0.5 | 37 | - | 98055A098 | \$8.62 / 50 | | Carriage Shoulders | M4x5x6 | 12 | - | 92981A146 | \$2.16 / 1 | | Reduction Shoulder | M4x5x10 | 1 | - | 92981A030 | \$2.32 / 1 | | Idler Shoulders | M4x5x20 | 5 | - | 92981A042 | \$2.33 / 1 | | NEMA 23 Stepper Motor | > 56mm Can Length | 1 | Spec Shaft with Pinion | [Stepper Online](https://www.omc-stepperonline.com/nema-23-stepper-motor/nema-23-bipolare-1-8deg-1-26nm-178-4oz-in-2-8a-2-5v-57x57x56mm-4-fili.html) | \$14.83 / 1 | | GT2 Pinion | 20T | 1 | Spec Shaft with NEMA 23 | [Amazon](https://www.amazon.com/Saiper-GT2-Teeth-6-35mm-Synchronous/dp/B07MGMBX3N/) (or) [RobotDigg](https://www.robotdigg.com/product/226/20-Tooth-2GT-Pulley-10pcs-per-lot) | \$9.96 / 5 | | GT2 Closed Loop Belt | 280T, 6mm Wide | 1 | - | [Amazon](https://www.amazon.com/280-2GT-6-Timing-Belt-Closed-Loop/dp/B014SLWP68/) (or) [RobotDigg](https://www.robotdigg.com/product/283/260mm-264mm-268mm-280mm-284mm-288mm-or-294mm-gt2-endless-belt) | \$15.88 / 10 | | GT3 Open Loop Belt | ~ 1m, 9mm Wide | 1 | - | [Amazon](https://www.amazon.com/Ochoos-Timing-Rubber-Backlash-5Meters/dp/B07MWD9D7V/) (or) [RobotDigg](https://www.robotdigg.com/product/597/3GT-9mm-or-6mm-wide-open-ended-belt) | \$15.00 / 1 | | 6806 Bearing | 30x42x7mm | 2 | x | 6806-2RS [VXB](https://www.vxb.com/6806-2RS-Bearing-30x42x7-Sealed-p/6806rs.htm) | \$12.95 / 1 | | M3 Inserts | Tapered, 3.8mm Tall | ~ 300 | - | 94180A331 | \$12.92 / 100 | | M4 Inserts | Tapered, 4.7mm Tall | 16 | - | 94180A351 | \$14.96 / 100 | | M5 Inserts | Tapered, 6.7mm Tall | 4 | - | 94180A361 | \$12.00 / 50 | | M3 Washers | 18-8 Standard Flat | 300 | - | 93475A210 | \$1.62 / 100 | | SHCS | M3x16 | 100 | Pinning T- to the wall, and pulley endmatter | 91292A115 | \$5.87 / 100 | | SHCS | M3x20 | 100 | Pinning T- to one another (?) | 91292A123 | \$6.78 / 100 | | SHCS | M3x25 | 100 | Pinning T- and X-es together | 91292A020 | \$7.23 / 100 | | SHCS | M3x45 | 8 | Pinning the 'squat' together | 91292A025 | \$12.21 / 50 | | FHCS | M3x10 | 30 | Pinning blisters to faces | 92125A130 | \$5.81 / 100 | | FHCS | M3x25 | (?) | - | 92125A138 | \$11.50 / 100 | | Steel Dowel Pins | 5x8mm | 10 | - | 91585A506 | \$8.40 / 25 | | Feet | M4 Stud, 15x15mm | - | - | 93115K881 | \$1.78 / 1 | | **Approximate Mechanical Total** | | | | | **\$446.80** | | Loadcell(s) | 10, 30, or 50kg | 1 | Choose Range for Sensitivity | [Amazon 50kg](https://www.amazon.com/Pressure-Force-S-type-Sensor-Cable/dp/B01F6IOW3G/) [Amazon 30kg](https://www.amazon.com/Pressure-Force-S-type-Sensor-Cable/dp/B01F6IOWDG/) [Amazon 10kg](https://www.amazon.com/Pressure-Force-S-type-Sensor-Cable/dp/B01F6IOW4K/) | \$39.00 / 1| | Loadcell Amplifier | HX711 | 1 | - | [Sparkfun 13879](https://www.sparkfun.com/products/13879) | \$9.95 / 1 | | Power Supply | 350W 24V LRS-350-24 | 1 | - | [Amazon](https://www.amazon.com/MEAN-WELL-LRS-350-24-350-4W-Switchable/dp/B013ETVO12/) | \$32.25 / 1 | | **Rough Control Total: Incomplete** | | | | | **81.20** | | **All Up** | | | | | **\$528.00** | `````` Jake Read committed Sep 30, 2019 67 `````` `````` Paloma GR committed Nov 16, 2019 68 69 ``````### PRINTED PARTS `````` Paloma GR committed Nov 22, 2019 70 ``````The number of parts in the Fusion (CAD) model do not match the actual number of parts that are required for the machine. We are in the process of validating the numbers, it is better to follow this chart: `````` Paloma GR committed Nov 16, 2019 71 72 73 `````` | Part | Spec | Count | Notes | Picture | | --- | --- | ---: | --- | --- | `````` Paloma GR committed Nov 16, 2019 74 ``````| Blister Mirror | - | 3 | M3 inserts | | `````` Paloma GR committed Nov 21, 2019 75 76 77 78 79 ``````| Blister | - | 3 | M3 inserts | | | Edge Idler | - | 3 | - | | | Edge Idler Mirror | - | 3 | - | | | Pulley | - | 3 | - | | | Matter | - | 2 | - | | `````` Paloma GR committed Nov 22, 2019 80 ``````| Matter Insert | - | 2 | - | | `````` Paloma GR committed Nov 21, 2019 81 82 ``````| Pincer Head | - | 10? | - | | | Pincer Shaft | - | 10? | - | | `````` Paloma GR committed Nov 22, 2019 83 84 85 86 87 ``````| Heart Rear Set | - | 3 | - | | | Heart Front Set| - | 3 | - | | | Heart Drive Reduce | - | 3 | - | | | Heart Drive Pinon | - | 3 | - | | | Heart Drive Cap | - | 3 | - | | `````` Paloma GR committed Nov 21, 2019 88 ``````| Squat | - | 2 | - | | `````` Paloma GR committed Nov 22, 2019 89 90 ``````| Stray Idler | - | 1 | - | | | Stray Idler Mirror | - | 1 | - | | `````` Paloma GR committed Nov 16, 2019 91 `````` `````` Jake Read committed Oct 18, 2019 92 ``````## Control and Interface `````` Jake Read committed Sep 30, 2019 93 `````` `````` Jake Read committed Oct 18, 2019 94 ``````DEX runs a [squidworks](https://gitlab.cba.mit.edu/squidworks/squidworks) controller. The `dex` branches of [cuttlefish](https://gitlab.cba.mit.edu/squidworks/cuttlefish) and [ponyo](https://gitlab.cba.mit.edu/squidworks/ponyo) contain code that is known to work with the machine. Again, more documentation for these controllers is coming, for now - consult the repositories. `````` Jake Read committed Sep 30, 2019 95 `````` `````` Jake Read committed Oct 18, 2019 96 97 ``````![c1](images/2019-10-17_dex-controller.png) ![c2](images/2019-10-17_dex-controller-zoom.png) `````` Jake Read committed Sep 30, 2019 98 `````` `````` Jake Read committed Oct 18, 2019 99 ``````## Comparison to Instron 4411 `````` Jake Read committed Sep 30, 2019 100 `````` `````` Jake Read committed Oct 18, 2019 101 ``````To see how we do against a real instron, I tested identical samples on the DEX as well as on an Instron '4411' with a 5kN load cell. In the plot below (I'm using cuttlefish to plot the .csv that I saved from Bluehill, the Instron software), the leftmost plot is taken on the 4411, and the lazier slope belongs to the DEX. `````` Jake Read committed Sep 30, 2019 102 `````` `````` Jake Read committed Oct 18, 2019 103 ``````While the samples fail around the same load, the difference in elongation is ~ 1.5mm wide: this is almost surely the machine's own deflection, stretch in the belts, etc. `````` Jake Read committed May 10, 2019 104 `````` `````` Jake Read committed Oct 18, 2019 105 ``````![dex-compare](images/2019-10-17_data-compare.png) `````` Jake Read committed Aug 28, 2018 106 `````` `````` Jake Read committed Oct 18, 2019 107 ``````This obviously warrants correction. One way to do this is to build a stiffer machine, however, we will be chasing up the cost and complexity if we do this. Rather, we should throw some more control at it. To start, we can circle back to our attempts at [subpixel tracking](https://gitlab.cba.mit.edu/calischs/subpixel_tracking), or attach a small linear stage directly to our fixturing elements. For this, I am imagining something like the [AMS5311](https://ams.com/as5311), which should do some 12 bits inside of a 2mm throw (for 0.4um resolution). Either can be added to existing systems, given network controllers / modular browser code. Since I want to integrate it elsewhere, it's likely that the camera option comes first. `````` Jake Read committed Aug 28, 2018 108 `````` `````` Jake Read committed Oct 18, 2019 109 ``````## Testing Notes `````` Jake Read committed Aug 28, 2018 110 `````` `````` Jake Read committed Oct 18, 2019 111 ``````The D683 ASTM Dogbones: `````` Jake Read committed Aug 28, 2018 112 `````` `````` Jake Read committed Oct 18, 2019 113 ``````![dogbones](images/astm_d-638_bonesizes.jpg) `````` Jake Read committed Aug 28, 2018 114 `````` `````` Jake Read committed Oct 18, 2019 115 ``````# Roadmap `````` Jake Read committed Aug 28, 2018 116 `````` `````` Jake Read committed Oct 18, 2019 117 ``````*2019-10-17* `````` Jake Read committed May 10, 2019 118 `````` `````` Jake Read committed Oct 18, 2019 119 ``````One complete DEX exists in the MIT CBA shop, and has been validated against an Instron 4411. Current efforts are twofold: `````` Jake Read committed Oct 04, 2019 120 `````` `````` Jake Read committed Oct 18, 2019 121 122 123 ``````(1) Working with the [materiom](https://materiom.org/) project (whose mission: to provide open data on how to develop bio-inspired materials for a circular economy), and the [fablab at cic](https://cic.com/fab), we are replicating the current design outside of the CBA shop, and building documentation while we do. (2) To improve the machine's test accuracy, we are integrating CV processing into the control architecture, to use [subpixel tracking](https://gitlab.cba.mit.edu/calischs/subpixel_tracking). Further controller improvements from the squidworks project will also bring rate control on-board. `````` Jake Read committed May 10, 2019 124 `````` `````` Jake Read committed Oct 18, 2019 125 126 127 128 129 130 131 132 133 134 ``````## Notes ``` - Where to build logs go? This repo -> gitlab, mtm.cba, etc. - Future integration of Temperature and Humidity Sensors - Higher quality integration of load-cell amplifier - Developing control for Cyclic Loading, Fatigue, etc. - Developing direct upload / websocket-to-database tools - Dec. 5: controllers -> CIC and London - Cuttlefish: manipulation, understanding, computing on test datasets in the browser. ``` `````` Jake Read committed May 10, 2019 135 `````` `````` Jake Read committed Oct 18, 2019 136 137 138 139 140 141 142 ``````## TODO ``` - encapsulate branches for ponyo, cuttlefish. - bs ? - put rpi setup back on desk with dex, branch, close - revisit with cameras, rate control `````````