# It Works-ish!

A project log for drillPresseur - Drill-Press with Force-Feedback

OK, most drill-presses have "force-feedback" in the normal sense... so this is a bit ridiculous.

Eric Hertz 12/06/2016 at 18:050 Comments

Actually wrote this before the log "Taking a step back...", but didn't submit it for some reason until now (12-15-16)... it's been sitting in a "tab" for quite some time...

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So, I've just connected two motors with encoders and a really simple feedback system for each, and between the two. Basically little more than,

``` power[n] = (desiredPosition[n] - actualPos[n]) * Kp[n]
```
and
```desiredPos[n] = actualPos[m] * PosRatio[nm]
```

And the results...?

I should just throw up some video... but it's *really* interesting to play with.

Messing with the ratios, it's kinda like having gear-reduction (or the opposite) between the two shafts. Except... SPEED-wise, it's like gear-reduction/increasion(?), but *torque-wise* it's like the exact opposite.

I dunno if I've got the ratios wrong or if it has something to do with the motor-drivers, or the motors, or the math, or what...

But just think about that for a moment... I mean, we've all a pretty good idea about what it's like to spin a tiny gear, and have it turn a larger one... (think of a bike).

Real gear-systems take a tiny bit of force on a small gear, but a lot of turning, to rotate the big one a little bit.

But in this case what's happening is a LOT of force and a lot of turning to rotate the big gear a little bit.

And equally-weird a tiny bit of force and a tiny bit of turning to rotate the big gear, causing the tiny gear to rotate *a lot*.

It's like gravity turned upside-down, or something... or one's first experience with cornstarch and water ("non-newtonian fluid"). A weird mind-bender.

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Force-feedback...? Yeahp, it seems to exist.

Unexpectedly, I'm feeling the additional force it takes to change the position of the motor slightly when it approaches a pole... and various other factors of the motors themselves, the resolution of the encoders, and more that has nothing to do with external loading.

This is some interesting shizzle... and also a bit dangerous. It's only drawn a tiny bit of blood so far.

But I'm quite tired, so we'll have to do more another day/hour.