Tuesday, December 22, 2009

Stepper Drivers and Ball Mice


A4983 Carrier

Stepper Driver

Here's one of my new stepper controllers. They can't put more than 0.5A into my 1.68 ohm motors from the 12v supply without overheating, probably due to current squared losses in the chips' fets. I will have to try a lower voltage. The white stuff is some heatsink compound- I was trying to heatsink the chip with little success. I will try something with a clip that goes under the board to hold it steady.


Quadrature Wheel

Ball Mouse Belly

Buffer

Being Used as Input

I'm using a gutted ball mouse as an input device. I'm picking the quadrature signals directly off the photodiodes, so they need some buffering. Quadrature translates perfectly to step/dir, so this allows precise bidirectional control of my stepper. With the A4983 set to 16x microstepping, I have 3200 steps per rev and therefore a wicked reduction ratio from the mouses' wheel. I'm re-splining my stepper shaft because the other splines weren't close enough to the motor body, and I already had this rig set up to test the drivers with. The arduino is in this circuit for two reasons: 1) to count pulses and tell me where I'm up to, and 2) to debounce the pulses, and provide them at a steady rate to my stepper controller to avoid missed steps and noise getting into it.


Overview

Re-Splined Shaft

Wednesday, December 16, 2009

Bearing Blocks and Print Settings


Y Bearing

360 Inner

Here's my first bearing block, two Y 360 inners put together until I can make matching outers for them. Since the angled bearings aren't perfectly straight and don't align perfectly, it has a tendency to spiral around the rod while travelling, about a quarter turn per 300mm of travel. I think I can clamp against this and overcome the friction until I can print new ones.

These blocks were quite fun to make from wood- lots of work with a bevel gauge, a saw and a wickedly sharp chisel. The holes were eyeballed and drilled out with a cordless drill, since I've had much better luck with this method than the pedestal drill, especially with odd angles.


Print Settings

For those of you having trouble getting prints to scale, the above shows the settings I use in gimp. Other image editors should sport similar settings.

Wednesday, December 9, 2009

Cutting splines into motor shaft for the extruder, and a start on Y bearing holders


Overview

Cut Splines

Dremel Raised

Cut Splines Close-Up

Here I am cutting splines into a motor shaft in preparation for my extruder according to Pinch-Wheel Variations on reprap wiki.


Motor Controller

L293D Close-Up

7 Ohms of Toaster Nichrome

I'm using my 7 ohms of nichrome to limit current to my stepper, since I don't have a chopper yet, and a 12v/20w dichroic globe to load the PSU's 5v line.


Y Bearing

360 Inner

"Y Bearing 360 Inner", although I haven't yet cut the bearing slots in the bottom yet. They'll have to wait for another day.

Tuesday, December 8, 2009

More Prints


Y Bearing 180

Y Bearing 360 Inner

Y Bearing 360 Outer

As you can see, I'm trying wireframe instead of translucent, until someone shows me how to render nice engineering drawings in blender with minimal work. Just turning off the wires between coplanar faces would be a start.

I'm slowly developing a picasa upload shell script which spits out thumbnail links, makes things immensely easier!

Z Bar Top Clamps and Z Idler Bracket


Hardwood Z Bar Top Clamp

Clamped onto Bar

Here's the close-ups of the hardwood Z top clamps. I drilled all the holes first then just cut down the middle with my hacksaw, so the two pieces are only a blade-width apart, and the cross-holes have perfect alignment. These new clamps feel very strong and I'm confident they'll survive much better than the last set.


Z Idler Bracket

Test Fit with some bearings mounted

Here's my latest part in-situ, the z idler bracket. It looks like this wood may be a bit soft, but we'll see how it goes. Maybe the washers will just dig in nicely?

Can also see the last of the studding cut to size in the last pic above. Those 418mm lengths through the Z Leadscrew Bases look a bit short to me, maybe make yours 430mm or so unless that's just some sort of error on my part.

Friday, December 4, 2009

Z Motor Bracket, Test Fit


Test Fit

Y Motor Bracket

Here's a test fit of all the parts I've made so far. You can also see my new hardwood Z bar clamps which I forgot to take a close-up of.


Z Motor Bracket

Bottom View

Here's my newest part. Looks like I'll have to touch up that horizontal hole with a hand drill or something, clearly it's not very straight.. For some reason, drilling a straight hole with my pedestal drill is almost impossible.

Tuesday, December 1, 2009

More Breakage


Section view of

Bearing Collar

Collar In-situ

Here's a section view of the collar I made to put M6 studding in a 608 bearing. Note the lengthwise cut which allows me to reduce the diameter enough for it to fit properly.


Broken Parts

These parts all broke because 6mm holes don't accept 6mm studding too well, especially when they're not particularly straight. Widening them out to 6.35mm (1/4") helps immensely, as does eyeballing them straight rather than relying on the pedestal drill. I filled the cracks with PVA and clamped them for the night. One of them had already split, and it split again on the other side indicating that the glue is stronger than the wood!


Motor Driver Overview

Motor Driver in operation

Quick shot of motor driver operating in its new location with some debug output on the screen.

Monday, November 30, 2009

Z Leadscrew Bases


Z Leadscrew Bases

with bearings and scrap studding

Z leadscrew bases with bearings and some scrap studding mounted. Fitting M6 studding into 608 bearings required a small collar, which I made from some spare 1/4" copper pipe. I cut the pipe lengthwise, squished it a bit to fit snugly on the M6 studding, then put it in the trusty pedestal drill and sanded it until the bearing fit. The M6 washers foul on the M4 washers around the bearing, so I'll need to cut them down a little.

Motor Driver


Motor Driver

Motor Driver

Here's my temporary stepper driver, which I will use until I build a proper one. Some parts of the construction need a working driver, eg putting splines on the shaft for the pinch-wheel extruder, and putting flats or keyways for the axis gears. It doesn't have proper current control, just a resistor, but it should be sufficient for now. I programmed up to 32x microstepping, although steps smaller than about 8x don't seem to have any effect at all - probably because the L293D is only rated to 5khz, but I'm driving it at 62.5khz.

Sunday, November 29, 2009

Made some more parts since my last post, check them out:

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Z Bar Top Clamp
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Z Bar Cracked

Clearly I cut the z-bar with the grain running the wrong way. I'll have to reorient and make some more, see if they survive better. Perhaps make them fatter?

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Y Motor Bracket
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Y Motor Bracket

I haven't cut out the opto-flag on these yet, I only got my "router" working in the past day or so. A router bit in a pedestal drill is the closest I have to a mill at the moment.

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Z Leadscrew Base
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Z Leadscrew Base

Z leadscrew bases, with my first work on my repurposed drill. I think the wood at the bottom of these may split under the weight at some point, but I'll deal with that when it happens.

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Ball Chain

You can still see the black marks on some of the balls in the ball chain where I measured its exact pitch. Turned out to be 4.77mm pitch, 3.6mm ball diameter, 3m for AU$12 at my local hardware store.

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NiChrome

From a toaster, so uninsulated. Considering insulating with aluminium, whose oxide is an excellent insulator while conducting heat quite readily.

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Ball Bearings

from Small Parts and Bearings who seem to be the only shop in Australia that has ball bearings in an online shop.

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Prints waiting to be cut

Various prints either made already or waiting to be made.