Another 3 Axis Position System for a RepStrap

Here is a link to another 3 axis position system for a repstrap. Looks pretty simple and obviously easy to assmble. The only issue--as I can imagine it--would be the difference in resolution due to using screws and not belts. Other than that, could this thing work?

[www.makezine.com]

Cheers!

Brilliant! He's using exactly the same geometry that I am for Tommelise 2.0, except that he has some detailing that is a hell of a lot more robust and simple than what I'd contemplated.

I see 3-4 things about his design that I am going to steal unashamedly.

Thanks for posting that link!

Edited 1 time(s). Last edit at 08/26/2007 03:22PM by Forrest Higgs.

No problem! Glad to finally be of some assistance...

Cheers!

yeah, his design look awesome. i'm going to have to look at that in more detail when i get home.

Very slick... that looks like a really nice lightweight design that should be a good match for reprap. If my first design doesn't work out, I'll probably try copying most of his. It'd be really nice to have a small machine that can sit on your desk instead of a heavy pile of lumber sitting on the floor.

i'm thinking perhaps we should approach this guy and see if he's interested in joining forces with us. it seems like he has quite a bit of mechanical know-how to bring to the table.

It was certainly a very slick design. I like the way he used the rails. It seemed like it would be so easy to just loosen a screw and adjust something, or replace a part. And that doesn't seem to be at the expense of too much reliability. From my experiences, machines with moving parts need to be designed as sturdily as possible, but simply, so that you can quickly adjust or replace injured pieces.

And the hardware store clerk was certainly right, if that were connected to anything wet, he would be having water all over the place! Who knows, maybe that could be considered a feature. Cooling, grime rinsing, or kinetic sculpture, take your pick.

Anybody know of a source for bearings that are mounted like his? I can't find anything similar at Lowes or in the McMaster catalog.

I recently bought a pack of 10 ball bearings on eBay. I think they come up quite regularly. I believe you can also get the ones intended for roller skates at a very resonable price.

---

[www.hydraraptor.blogspot.com]

yup, you can get rollerskate bearings for ~$1 to $2 / each. they are standard 608 bearings. you can even shell out to get more expensive ones, but the cheaper ones work just as well.

What they said. I got a pack of 16 at Dick's sporting goods, somewhere in the $30 range. I remember Amazon had a few listings for rollerblade bearings if you can't find them locally.

hey guys,

just wanted to let you know that i did a bunch of work on this design, and i've created some pretty detailed CAD drawings of it. i'm going to attempt to get the design lasercut, and will keep you guys posted of my progress. i'd love to get some feedback on the drawings I did.

wiki page: [reprap.org]
blog entry: [builders.reprap.org]

Nice job!
I'll have a look at it!

Zach,
do you have a list of parts for this yet mainly pipe length??

Bruce

It looks like you are replacing the pipe base with a sheet of something (acrylic? metal?) The Z axis will be supported by an L-shaped pipe assembly with floor flanges on both ends?

I started on one of these (pretty-much true to the original design) last week. The X and Y stages are working well, so far I'm pretty pleased with it.

Some things to watch for: the gantry is going to be relatively heavy. You'll need to make sure the base is pretty darn rigid. I don't have any acrylic lying around to play with, but 1/4" sounds marginal for the stages and way too thin for something that has to support the gantry. If you decide to counter-sink the 10-24 bolts holding the channel to the stages, that's going to eat a fair ways into your 1/4" of material. You can probably still get it to work since there won't be much of a load on any of the parts.

It looks like the X and Y stages are the same size, both as big as the base. You should be able to save a fair amount of material by cutting those down to closer to the actual usable area. You're not going to be able to push the stage more than half way off the side in one direction, and with the original design you won't be able to move it over the motor on the other side.

Pay attention to the height of everything. I used 3/4" wide x 1/2" channel, so I had 1/4" less room to work with than you will. Anyway, a NEMA-17 motor is still more than 1.5", so you're not going to be able to slide the platform over the motor unless you alter the design to allow more than .75" clearance between stages. Even some of the things you think would be thin might not be, depending on how you make them. If you use a machine screw and nut to mount the bearing, it can get kind of thick... probably three washers + the thickness of the arm + the thickness of the bearing + the thickness of the nut. Still likely ok for you, but it wouldn't have worked on my 1/2" rails.

If you changed the direction of the stages (Y on the bottom), you could mount the Y motor in the dead space next to the floor flange.

b_wattendorf Wrote:
-------------------------------------------------------
> Zach,
> do you have a list of parts for this yet mainly
> pipe length??
>
> Bruce

not yet. all the pipe is standard 1" black iron pipe. here is a rough list:

2 x threaded flanges
1 x 90degree elbow
1 x 10" pipe
1 x 4" pipe

those 10" and 4" are just guesses at this point... i'll know once i actually assemble it.

emf Wrote:
-------------------------------------------------------
> It looks like you are replacing the pipe base with
> a sheet of something (acrylic? metal?) The Z axis
> will be supported by an L-shaped pipe assembly
> with floor flanges on both ends?

yup... exactly.

>
> Some things to watch for: the gantry is going to
> be relatively heavy. You'll need to make sure the
> base is pretty darn rigid. I don't have any
> acrylic lying around to play with, but 1/4" sounds
> marginal for the stages and way too thin for
> something that has to support the gantry. If you
> decide to counter-sink the 10-24 bolts holding the
> channel to the stages, that's going to eat a fair
> ways into your 1/4" of material. You can probably
> still get it to work since there won't be much of
> a load on any of the parts.

sorry, i wasnt more specific... both the vertical base and horizontal base are going to either be 3/8" or 1/2" acrylic. you could also very easily make it out of MDF.

the rest of the parts are going to be 1/4" acrylic. (x/y/z stages, bearing arms, etc.)

> It looks like the X and Y stages are the same
> size, both as big as the base. You should be able
> to save a fair amount of material by cutting those
> down to closer to the actual usable area. You're
> not going to be able to push the stage more than
> half way off the side in one direction, and with
> the original design you won't be able to move it
> over the motor on the other side.

yeah... i'm thinking about either having the rails extend out by 2x their drawn length, and just hanging over the base, or using a much larger base and attaching them to it. i think this is something i'll modify once i actually have some real experience with the machine.

> Pay attention to the height of everything. I used
> 3/4" wide x 1/2" channel, so I had 1/4" less room
> to work with than you will. Anyway, a NEMA-17
> motor is still more than 1.5", so you're not going
> to be able to slide the platform over the motor
> unless you alter the design to allow more than
> .75" clearance between stages. Even some of the
> things you think would be thin might not be,
> depending on how you make them. If you use a
> machine screw and nut to mount the bearing, it can
> get kind of thick... probably three washers + the
> thickness of the arm + the thickness of the
> bearing + the thickness of the nut. Still likely
> ok for you, but it wouldn't have worked on my 1/2"
> rails.

definitely. i'm going to use 3/4" x 3/4". once i get real things, i'll be able to specify exact screw length, etc. thanks for the heads up.

> If you changed the direction of the stages (Y on
> the bottom), you could mount the Y motor in the
> dead space next to the floor flange.

thats actually where it is going to go... it hangs off the top side of the x axis. i've based the drawing size off nema 17 motors, but there is enough space that nema 23 would probably fit too. i allowed for a good amount of clearance between the x axis + motor and the vertical pipe.

Zach,
What was wrong with the original steel pipe design? It looked like a clever way to get stiffness. If you change to acrylic you might get away with it for FDM but it will no longer be any good for milling. It seems a shame to downgrade the design like that unless you have a good reason. I think a lot of people are also interested in owning a small mill. You can boostrap another step that way by milling your own extruder like I did.

---

[www.hydraraptor.blogspot.com]

ZachHoeken Wrote:
-------------------------------------------------------
> sorry, i wasnt more specific... both the vertical
> base and horizontal base are going to either be
> 3/8" or 1/2" acrylic. you could also very easily
> make it out of MDF.

Ok, that should be fine

> thats actually where it is going to go... it hangs
> off the top side of the x axis. i've based the
> drawing size off nema 17 motors, but there is
> enough space that nema 23 would probably fit too.
> i allowed for a good amount of clearance between
> the x axis + motor and the vertical pipe.

Cool... I'm no good at reading these drawings. NEMA 23 is going to be awfully close to riding on the base plate, but you can always put wheels on the motor :-)

You might want to make some provision for mounting a piece of wood on the top surface to extrude on. Maybe a two holes on each edge of the upper stage that you can either put in some clips to hold down a piece of wood (or bolt the surface directly to the stage).

nophead Wrote:
-------------------------------------------------------
> Zach,
> What was wrong with the original steel pipe
> design? It looked like a clever way to get
> stiffness. If you change to acrylic you might get
> away with it for FDM but it will no longer be any
> good for milling. It seems a shame to downgrade
> the design like that unless you have a good
> reason. I think a lot of people are also
> interested in owning a small mill. You can
> boostrap another step that way by milling your own
> extruder like I did.

there was nothing wrong with the original design, and if using acrylic for the base proves to be a wrong move, it will be easy to change back to the original pipe based design.

one of the problems with the original design was that you had to drill holes in the steel pipe. when drawing it, i didnt know the exact dimensions of the pipe, so i decided to replace the base with something lasercut, and acrylic that i could control the dimensions of.

if it really is a bad idea to use acrylic as you say, then i'll stop by the hardware store to get the parts, and then go ahead and assemble them so that i can take measurements. from those measurements i should be able to create printable templates that we can offer for people to drill the holes with.

now that i think about it, its probably a good idea to go back to steel pipes for the frame, and provide templates. both for strength, as well as making it cheaper (the 1/2" acrylic base is going to be very expensive)

>
> Cool... I'm no good at reading these drawings.
> NEMA 23 is going to be awfully close to riding on
> the base plate, but you can always put wheels on
> the motor :-)

yeah... i'm no good at doing both the x/y drawings and adding in the Z dimension in my head. i was planning on getting the design mocked up and then experimenting to see how things fit together, and if any changes need to be made.

of course if we switch back to using steel pipe for the whole frame, then the motor has more built in clearance.

> You might want to make some provision for mounting
> a piece of wood on the top surface to extrude on.
> Maybe a two holes on each edge of the upper stage
> that you can either put in some clips to hold
> down a piece of wood (or bolt the surface directly
> to the stage).

yeah, that would be nice. i'm doing something similar for the tool mount stuff, so i'll try and do something like that for the Y mount as well.

I'm pretty pleased with the original design (using pipes). I went with 3/4" and they're rigid enough for anything I'm going to want to do with it. The design has some really nice features for building without fancy tools. One of the nice surprises was that you don't have to work hard to make the axes orthogonal. If you're using something that has two sides at right angles for the X stage (cutting board quarters for me), you can simply clamp the channel flush with the edges, then drill and bolt them in place. Nothing else has to be measured that precisely.

One thing I think McWire did but didn't mention anywhere was tap threads into the holes in the pipe. I happened to have a 10-24 tap so I did the same, and it does make for a bit cleaner assembly than drilling through the pipe and running a bolt through. I think he also used it on both sides of the bearing arm (just figured this out now). On the bearing side, it allows him to have nothing protruding from the top side of the arm. On the side that attaches to the stage, it makes for easy assembly and makes the act of screwing the part on tighten it against the rail. If you just use a nut & bolt like I did, the bolt will just spin when you tighten it, so you have to snug it up to the rail yourself. I'll probably glue or solder the nut to the arm to get the same effect.

Tools I used: hand drill, hacksaw, screwdrivers, pliers, hammer & center punch, bench vise, C clamp, countersink bit, pipe wrench, combination square, file, tap.

nice. i think i'll change the design back to being based on those pipes. hopefully i'll find some time this week or next to actually get in the shop and attempt to build one.

for the holes on the pipe, i was planning on using self-tapping screws. i've used them before and they work great.

Hmm...
With this in mind, will you be offering the quick-change assembly that's intended for 2.0?
If I use this, I'd very much like to be able to quickly swap the extruder out for a rotary tool. Esp, as the original author did, in fact, use a rotary tool, on this design, to turn out "printed" circuit boards.

ZachHoeken Wrote:
> for the holes on the pipe, i was planning on using
> self-tapping screws. i've used them before and
> they work great.

Darn, I never think of using them for this sort of thing. Should be a lot lower-stress than hoping your tap doesn't break at an inopportune moment. I'll have to pick up a few to play with next time I'm in the hardware store.

Roach_S Wrote:
-------------------------------------------------------
> Hmm...
> With this in mind, will you be offering the
> quick-change assembly that's intended for 2.0?
> If I use this, I'd very much like to be able to
> quickly swap the extruder out for a rotary tool.
> Esp, as the original author did, in fact, use a
> rotary tool, on this design, to turn out "printed"
> circuit boards.

sort of.

the darwin mounting thing is based on 3D printing. i have considered that you'd want to switch tools rapidly, and the design actually incorporates this. instead of mounting tools directly to the Z axis, there are mounting holes on each corner that will allow you to easily mount whatever you want. the Z carriage is also large enough that you could mount the controlling circuit board directly to it.

that way, replacing a toolhead is as easy as unscrewing 4 wingnut bolts, and disconnecting it from the network/power.

to make a new tool mount, simply take the template (or a premade reprap / dremel /etc. ) mount, and attach your tool. its just a flat piece of acrylic, so it should be pretty easy to figure out how to attach something to it.

Okay guys I'm sorry but I have a stupid question to ask. Will this new robot design require new firmware? I'm expecting my picprogrammer in a few days and would like to know if I should hold off programming my pics?

i dont think so.

if anything, it will be a change in your host software configuration file. one of the nice things that we've done a pretty good job of so far is to keep the systems modular: any 1.x board will work with any other 1.x board, the cartesian bots should all be compatible, extruders can be hooked to any cartesian machine, etc.

well, i placed my order today for the laser cut parts. for a one-off run, it cost me $140. i did a few things to experiment, like having big text... once i find out how the small text looks, i'll probably revise the text to the smallest possible. the text was about $25-$35 of the cost of the cutting. Also, on a larger order, we will get a bulk discount, which will probably be 30-40%, which brings the price down to around $100.

so, lets do a bit of speculative math here:

lasercut parts: $100
piping/nuts/bolts/rails/etc (from mcmaster): $50
motors: (cheap, nema 17's): $60
electronics (boards + components): $140
extruder: $50

that brings the total cost for getting a functional repstrap machine down to $400. lasercut parts are well suited for small-medium scale manufacturing, self-replication, as well as being hand made (built-in printable templates, baby!!)

if this design works out well, then we'll be able to offer a kit within *weeks* of proving that it works. the electronics stuff is done. we're 4 weeks away from getting more extruders in stock.

talk about exciting!

Keep us posted Zach, I for one am excited to see development moving ahead and a new robot design could be a shot in the arm for reprap. Is the text necessary?