first pi project

Plan
Pursuant to my aforementioned automated storage/retrieval project, I'd ordered a bunch of hardware.  I've played with Arduino before, and this time i wanted to try a raspberry pi.

Equipment
I ordered:
* raspberry pi, model 3b -- $30 for a pretty full-featured computer!
* a microSD card, since the pi needs it.
* a pi "cobbler+" (which lets me easily use the pi's pins on a breadboard and, more importantly, labels them)
* a pack of 5 steppers, each with a small driver board (more on these later)
* some timing belt and pulleys

I had:
* various power supplies, and a voltage converter/regulator
* breadboard
* wires and jumpers and alligators
* a battery bank (because the pi needs more juice (2+ amps!) than any of my micro USBs supply)

Setup

An old ATX computer power supply supplies 12v to a buck converter/regulator that sends 7.3v to the motor driver.
The battery bank supplies 5v at 2A to the pi, which (via the cobbler and breadboard and some jumpers) sends control signals to the motor driver based on a python program i stole from the internet and slightly adapted.
The motor driver sends the stepper a simple instruction on which coils to energize.

Picture
Result
the result was the slowest turning motor you have ever seen - like, maybe 2 rpm.  I was underwhelmed.  With some tweaking (using full rather than half steps, reducing the delay between steps) I was able to get it to a roaring 10 rpm -- still far too slow to actually use in a project.

Lessons Learned
I later realized the motors are geared way down, about 64:1.  So they're nice and torquey, but very slow.  I could steal some of that speed back by putting a big gear on it, but i don't have any gears and I'm not sure these are the motors i want to use.  They're definitely good for prototyping and nice and cheap for several, but if i proceed with this project i'll probably go bigger.

The pi needs more juice than i thought.  I intended to use a normal micro usb charger (i have oodles), but the current demands are more than i thought by a long shot.  The battery bank was sort of a hack, i don't want to always drain it while projecting.  I'll need to order a bigger supply for the pi.  I think i probably reduced its demands by disconnecting it from the monitor, keyboard, and mouse and used SSH to get in from my laptop (via the wifi which the pi natively supports -- awesome).

I am not really well set up to do small mechanical things.  I mounted the pulleys on makeshift shafts which i shoved into holes i drilled in a 2x4.  The prototype is not as polished as it could be.  I should get an erector set or something.

The cobbler ribbon cable is easy to connect backward.  Fortunately i didn't break anything - it just happened not to work, so i reversed it.  it should have an indicator or something.

I can actually make a motor turn!

Comments

Post a Comment

Popular posts from this blog

forgery

Image
 Ronny and Matt from Church invited some youth to try simple forging.  Ronny brought an anvil and some know-how.  Matt brought a little propane forge. Starting from some simple rod stock, a couple guys each got to pound on the red hot metal: to make a stylish little letter-opener:  I got to hammer too, and made a wee "garlic cleaver": I didn't do much of the metal - i just supplied some dumb hammering while Ronny moved the work - but I was proud of the handle: I cut off 5" of an oak branch that had fallen during the recent storm, shaped it with a rasp, then burned it with a blowtorch to get the color.  I sealed it with a quick clear coat spray.  The handle only took about 90 minutes (mostly the rasp), and I was pleased with the comfort and color. I mounted it on the blade by drilling a hole in the wood (slightly undersized for the tang), heating up the metal to really hot, and shoving them together.  The hot metal burned its shape into the woo
Read more

The way it goes

I wanted to install a ceiling fan where there was only a ceiling light.  No problem!  I've done this many times before - maybe 30-45 minutes is plenty. HAHAHAHAHHAHAHAHAHHAA! As so often happens in projects, this one snowballed and wound up taking over 3 hours .  Follow along with these easy-to-repeat steps and see if you can tell where the problem lies: Step 1 - Remove the old light fixture finger screws for the glass bowl -- easy peasy. a screw or two holding the light housing to the junction box --  boy, this box is pretty wiggly. the wirenuts and ground wire connecting the light to the supply --  hot wire is off; all is well. Pro tip: It's a good idea to turn off the breaker, but chances are good your breakers are labeled incomprehensibly or are outright lies.  What I do is turn off the room switch and then quickly tap the hot wire with a finger to see if i get zapped.  I didn't this time! Surprise!  A pleasant surprise!  The power supply run to the
Read more

Bridge Construction

Image
We had a bridge going over a small stream in the back yard.  HAD.  Two years ago: Following some rain and flooding, it washed about 70 feet downstream and lodged against the fence: Because it was heavy (it's about 16x8, made of treated wood, with some steel and 12x12 timbers on the underside -- i have no idea how it floated), nothing i had could drag it back, certainly no without destroying it. I paid my kids to disassemble it - they spent probably 12 hours each with crowbars and a sledge hammer.  They stacked the wood and put the steel in the barn.  Awesome. I used some of that wood to build forms for a new concrete footer on each side -- there were some concrete blocks it had been resting on, but this time wanted more. As usual the hardest part is measuring and leveling stuff.  At least the stream was low, but schlepping stuff back and forth is hard. I got a harbor freight cement mixer, since i was going to be doing probably 1500lbs of concrete and mixi
Read more