End of the line here is (1) to do small-scale material testing, OK. Next step is (2) to automate material search, doing a kind of real-time simplex where function evaluation is testing and DOF are process and recipe parameters. This is a cohesive, realizeable story.
I would like to know:
- evaluation: pick: Stiffness and Tensile Strength? some weighted score from both?
- ... no hard yesses, want to be able to pick & make
- so far doing tensile strength and elastic modulus
- to add: poisson ratio with vision and actuation
- inputs: if we are to pick, say, 3 process parameters (to have 3D search space), what are they?
- water, glycerin, agar
- humidity and temperature / during drying time
- heating profile ... how long the cook is
## FEA
I ran a quick simulation to see that this flexure was OK. Here it is loaded in the direction it is meant to be stiff in, with 2.5kN applied vertically. There are two of these members being tested so this would be equivalent to 5kN of force, about where I expect this thing to top out. Displacing about 40uM (I'm looking at the face-to-face distance between the loaded zone and the fixed zone, not that rotation that appears from my non-rigorous fea constraints) with 70MPa stress maximum.
And out of plane, with 250N applied, about 20uM displacement. So 1/10th the load and 1/2 of the displacement, it's at least 5x stiffer in one DOF than the other. Is that grounds for a decent flexure?
## The Cutting
0.1mm offset, 0.5mm fillet for test.
## Next Steps
design tasks remaining
- fixturing
- dbner ... in gh
- minor offsets for fits
- measure material carefully
- confirm sdp-si parts fitments
- control box ? psu home ?
- fab this thing
- finish waking up new network, new stepper boards / code
- finish hello-world CV on markers
- plot a stress/strain chart
- show high resolution stress / strain measurement w/o high stiffness machine
- show machine reference via known material?
## Generalist does uSSM
To test requisite parts for a small stress and strain machine, I attached some jaws and a load cell to [this 'generalist' machine](https://gitlab.cba.mit.edu/jakeread/mothermother).
I used [automatakit](https://gitlab.cba.mit.edu/jakeread/automatakit) network controllers and [atkapi](https://gitlab.cba.mit.edu/jakeread/atkapi) to program the beginnings of a materials testing system: here I'm just stepping the axis along 25 steps at a time and capturing a photo on each step. No data yet.
We're going to try to track the endpoints with CV, rather than fancy encoders etc. Sam has done some prior work on this, [here](https://gitlab.cba.mit.edu/calischs/subpixel_tracking).
# Microphone Stiffness Testing
[Alisya did this in FabAcademy](http://archive.fabacademy.org/2017/fablabsantiago/students/356/project.html) and it would probably be a fun piece of kit / example for the NIST Project. Looks pretty simple... and compelling.
# Design Spec / Notes
The goal here is to design and build a machine, which can be fabricated in $250k size fab labs, that can generate stress-strain curves for a wide set of materials as well as perform hardness testing.
To ballpark, I'd like to see 100mm diameter plates having a total travel from 0mm separation -> 500mm, this leaves enough room for fixturing etc.
## Drawingboard Return
instron:
redo, this is untenable and no one should build one
beams all the way down, overconstrained, and motors in front
nut-in-hole type threading,
10mm width S5M pulley: but check torque spec
- at this width keyless works very well w/ 16mm total width https://us.misumi-ec.com/vona2/detail/110300409350/?CategorySpec=00000045557%3a%3ac
- compare: fancy-ass pulleys with medium reduction, or 1/2" -> 10mm coupling and NEMA34 ? ... consider that reasonable torques for a shaft coupling are '35 - 53' in-lbs (from McMaster search: 2764K424 or 2464K34) - that's about 5.6 Nm, a NEMA34 does ~ 5-8Nm at the upper end, so it's in threshold
- coupling is ~ $100 each for well-spec'd, $72 each for ok-spec'd ... pulleys are probably similar once you've done 2x pulleys and 1x belt, with fancy shit... and pulleys afford smaller motors that you can actually drive,
- if, however, you can find cheap couplings, to spec (probably not) you can do that. get your spreadsheets back out !
## Generating kN
...
...
@@ -150,6 +69,16 @@ Racks aside, a ballscrew is the obvious way to do this. Ballscrews can be had fo
For the same ballscrew, to achieve 12 micron resolution we'll only need 416 steps in each rotation - this is easy to get.
## Design Spec / Notes
The goal here is to design and build a machine, which can be fabricated in $250k size fab labs, that can generate stress-strain curves for a wide set of materials as well as perform hardness testing.
To ballpark, I'd like to see 100mm diameter plates having a total travel from 0mm separation -> 500mm, this leaves enough room for fixturing etc.
Sam's note: the ballscrews should be 'pulling' in all cases. Against their fixed, driven side. This is a good note, thank you sam.
---
## Step Two: Force Measurement
For load measurement, Sam has worked through a great [loadcell](https://gitlab.cba.mit.edu/calischs/loadcell) design.
...
...
@@ -160,8 +89,69 @@ Ok, doing this with a wheatstone-bridge type load cell now.
I believe I want my ADC to have the green line 'on top' and white on the bottom, of a differential channel.
---
## Fixturing
! important
---
# uSSM \#2
**status** machine is designed, fabricated, waiting for adaption of fixturing from 'the generalist' and for squid works controllers.
## Dedicated uSSM
Here I'm using some
- Ballscrews, SFU2005 C7 700mm Long [ebay, $150](https://www.ebay.com/itm/SFU2005-Rolled-Ballscrew-C7-Anti-Backlash-Ballnut-L300-350-400-450-500-600-1000/202274175696?hash=item2f187afad0:m:m2SEqt9q_ykYYkrO5ZM9deA:rk:1:pf:0)
- Nema 23 Motors w/ .25" Shaft
- GT2 5mm 6.35mm Bore Pulley 12T for 15mm Belt 'A 6A55-012DF1508'
- GT2 5mm 12mm Bore Pulley 48T for 15mm Belt 'A 6A55M048NF1512'
- GT2 5mm 15mm Belt with 55T 'A 6R55M055150'
- http://shop.sdp-si.com/catalog/product/?id=A_6R55M055150 55T 15mm Closed GT2 Belt
I ran a quick simulation to see that this flexure was OK. Here it is loaded in the direction it is meant to be stiff in, with 2.5kN applied vertically. There are two of these members being tested so this would be equivalent to 5kN of force, about where I expect this thing to top out. Displacing about 40uM (I'm looking at the face-to-face distance between the loaded zone and the fixed zone, not that rotation that appears from my non-rigorous fea constraints) with 70MPa stress maximum.
And out of plane, with 250N applied, about 20uM displacement. So 1/10th the load and 1/2 of the displacement, it's at least 5x stiffer in one DOF than the other. Is that grounds for a decent flexure?
---
# uSSM \#1: Generalist does uSSM
To test requisite parts for a small stress and strain machine, I attached some jaws and a load cell to [this 'generalist' machine](https://gitlab.cba.mit.edu/jakeread/mothermother).
I used [automatakit](https://gitlab.cba.mit.edu/jakeread/automatakit) network controllers and [atkapi](https://gitlab.cba.mit.edu/jakeread/atkapi) to program the beginnings of a materials testing system: here I'm just stepping the axis along 25 steps at a time and capturing a photo on each step. No data yet.
We're going to try to track the endpoints with CV, rather than fancy encoders etc. Sam has done some prior work on this, [here](https://gitlab.cba.mit.edu/calischs/subpixel_tracking).
---
# Microphone Stiffness Testing
[Alysia did this in FabAcademy](http://archive.fabacademy.org/2017/fablabsantiago/students/356/project.html) and it would probably be a fun piece of kit / example for the NIST Project. Looks pretty simple... and compelling.
