Commit 339dedb8 authored by Jake Read's avatar Jake Read

add first pull video, cad for mm-instron, etc

parent e0325f17
# micro Stress vs Strain Machine
## Spec!
## Progress
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).
![machine](images/ussm-at-mm.jpg)
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.
![cam](images/ussm-1-camera.jpg)
![bone](images/ussm-2-bone.jpg)
![neck](images/ussm-3-neck.jpg)
![gif](video/first-pull.mp4)
Probably the most interesting point is that Sam and I have decided to try using a webcam and some computer vision to track the position of the speciment endpoints. He's done some prior work, [here](https://gitlab.cba.mit.edu/calischs/subpixel_tracking).
## Next Steps
- wake up ADC / find external high resolution ADC
- hello world computer vision on markers
- show high resolution stress / strain measurement w/o high stiffness machine
- show machine reference via known material?
# 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.
......@@ -52,6 +75,12 @@ From our 18mm diameter pinion having a circumference of 56mm, this means 4667 co
All in, a direct rack and pinion drive can land us at a 2kN machine with some desired resolution, but we're at or near most of the limits here.
### Belts
![img](images/belts.jpg)
Since I was spinning this up to test on a belt-driven gantry system, I was able to confirm that this is a bad idea. We defeat the elastic stretch of the belt by measuring at the specimen (not through the machine's structural loop) but a meagre GT2 belt profile skips teeth pretty quickly as we approach any tens of kilos of load.
### Ball or Leadscrews
Racks aside, a ballscrew is the obvious way to do this. Ballscrews can be had for less than hundereds of dollars. Besides transmitting motion smoothly, their ratios are favourable. For example, with a 5mm pitch ballscrew having an efficiency of 85%, we can drive 14kN with our 13Nm motor - so 28kN for the machine.
......@@ -64,6 +93,12 @@ For load measurement, Sam has worked through a great [loadcell](https://gitlab.c
![cell](images/sam-as5011-loadcell.jpg)
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
\ No newline at end of file
![img](images/jaws.jpg)
! important
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