Pirated CupCake

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CupCakeStrap

Release status: Working

CupCakeStrap3.jpg
Description
Cupcake as RepStrap
License
Author
Contributors
Based-on
Categories
CAD Models
External Link



This is an in-progress build
This project is made 90% from kludge and improv hackery. It is not meant as a tutorial or even a rough guide so much as it is intended as inspiration.

CupCakeStrap Basics:

True DIY should be done on the lowest operating budget possible

The CupCakeStrap is the high-school Senior Project of Benjamin Rockhold and Griffin Nicoll. It is a CupCake made from as close to scratch as possible, with the excepton of PCBs, Steppers, and PSU. Everything else was purchased in individual components from "The Internet" and a few local hardware stores. The plastic and plywood parts were laser-cut with Roosevelt High School's laser cutter and free material from donation. The CupCakeStrap is different from normal CupCakes in that it has been modified to reduce the price of some important parts, and it is not intended as a final machine. Instead, it will serve to print out parts for its successor, a RepRap Mendel-derivative (similarly modified for low cost). Thus, it is a RepStrap in spirit and a CupCake derivative in body.

CupCakeStrap3.jpg

So, I bet you're asking "What's the attraction to building a Cupcake, with its smaller print area, high price, and odd naming?" Well, first off, it's the cutest of printing machines. Secondly, if it's not going to be purchased outright from Makerbot, it's really not very expensive at all. I'm not trying to say that the machines Makerbot sells are not excellent or are over priced, but the draw to make one from scratch is pretty strong.


The following is basic documentation, not in any real organized form. This is a to-do item :p

CupCakeStrap Hardware

All of the Hardware variations from the original CupCake.

Improvisations Made for Low-Price

We decided that in order to maintain a low price, we ought to custom-build more parts than we have to order in a completed state. Basically, these modifications were made anywhere we thought we could save a buck without reducing functionality.

Acrylic Pulleys

Pulleys

To produce pulleys for zero cost, we found random belts from a scrapped printer (a BIG one, new printers use really small and useless belts) that looked similar to the ones used on the real CupCake, and then measured them. Using Inkscape, we performed a rotation of the tooth profile into a circle, and modified it to work with warping and stretching. Then we just lazzored them out of thin acrylic, and fused the layers together with an acrylic solvent. To attach to the motor, we used some random rubber things from the same printer, used to move paper. The rubber is a short tube, and very stiff. It was about 10mm in external diameter, and about the same as our motor's shaft in internal diameter. We insert the tube into the pulley, then press it onto the motor shaft. It's way, way stronger to hold in place than the motor can torque.

Cheap Linear Bearings

Linear Bearings

Rather than buy "real" linear bearings, we picked up some M8 Aluminum rod ($3 per meter) and some 8mm internal diameter brass tube (30cm for $4). With this, you get a sub-$10 brushing. We cut 6cm lengths of the brass tube and inserted them into a modified X stage (bearing holes reduced to diameter of brass rod). We made 3.5cm lengths for the Y stage, modified the same way. Essentially, we reinvented the brass brushing. These bearings work very well, even without lubricant. The primary source of friction is the motor on the XY stages and our motors are have excess torque, so friction is not a problem anyway. We feel these have a good chance and proving to have similar if not equivalent functionality as the proper ones originally intended for the Makerbot CupCake.


Improvisation Made for Increased Functionality

Now and then in the build process, we found things that we thought could be improved from the original CupCake. These are not particularly critical to the machine, but make it look better or work better (open to interpretation).

Motor Cut-Out

Motor Space Cutout

The motors we ordered (from Ebay) were more than 1cm longer than we expected, and so the Y-Stepper that rides the X-Carriage was too long to fit in the room given to it. We cut a large rectange out of the middle platform to correct this, and furthermore had to slide the PSU further forward in the machine. This means the PSU is 8cm in from the back plate. We have secured it with packing tape.

Extra Bearing Holders

Bearing Holders

The original CupCake has bearings on the bottom end of the Z-Stage rods that stick up from the 4mm plywood used. These look kinda bad, so we added an extra few mm of acrylic cut to fit the bearing and to resemble the Z-Stage bearing capture layers. These extra layers are essentially cosmetic, but they also make it harder for the bearing to escape its hole. Theoretically, they could be augmented with a bearing-capture layer, and this would make the upper capture layers unnecessary. That might look nice.

Z-Platform Nut-locks

Platform Locks

We decided that allowing the nuts to come lose from the Z-Stage was not something we wanted to see, even in the event of a head-crash. We added two more layers to the nut holder to fully trap it, a layer that mimics the platform's shape, and another Z-Guide part. We are going to have to modify the extruder-holding dinos to release the head in event of a crash, but that is a to-do item.

In the future, we may exchange the Z-platform for a plywood one, as we have heard that after extended operation the acrylic ones can begin to warp from the heat.

CupCakeStrap Electronics+Software

Not too many modifications were made to the electronics for the CupCakeStrap, but it has an interesting history and mix of parts.

Electronics

Original Electronics

The CupCakeStrap was originally designed around the RepRap Generation 3 electronics, build by hand from components ordered from Mouser and Digikey. Due to backorder issues, we purchased the wrong linear regulators, and wholly left out the SD card slot, large 5v resistor, and the female headers. When powered on, one of the linear regulators (completely wrong for the job) sparked and smoked. The board it was attached to died (painfully I am sure), and the others were saved, and had the regulators amputated. Loss of the linear regulators proved hard to work around. A solution whereby we tapped the unused 5v supply from the PSU was proposed on the RepRap IRC, and this solution worked! By taking 5v from the ATX jack and feeding it to the output pad of the stepper boards we were able to operate the boards, now supplemented with a Stepper Driver 1.2 for the Z axis. After finally getting everything running, the CupCakeStrap performed two "prints," with no toolhead. However, on the third power-on one of the remaining 2.3 stepper boards began emitting ozone and shortly after a capacitor began sparking and then detonated with a puff of smoke and flame. The burn damage was significant, destroying the traces around the capacitor as well as two resistors. These parts were re-ordered, at some cost. Believing this board to be inert and with no immediate way to repair it, we decided to bite the bullet and purchase some completed boards as a replacement. We purchased three new stepper boards from Techzone, as they are new, interesting, and I do not think any other CupCake has ever been equipped with them. These boards are not yet reconciled into our price breakdown, as we have not decided if the accidental damages should be counted into the CupCakeStrap's price. They will probably not be. We were able to recover the burned board on the same day the new boards arrives, and we performed a test with it to be sure. However, the new boards proved to perform slightly better, and do not heat up as much as the 1.2 board. They are also really, really small. The original boards will be returned to CupCakeStrap after she has competed printing her first child, which will probably inherit all of the current electronics, leaving CupCakeStrap with An Arduino and various mismatched driver boards.

CupCakeStrap's extruder is currently a Plastruder mk4-type design, with pinch-wheel and gearmotor. This is the only extruder that will be able to be driven given our time constraints, though designs for a NEMA-23 stepper driven "Paxtruder" derivative have produced a prototype/functional design. We cannot drive a stepper motor extruder with the current extruder firmware however, so we will need to upgrade to the reprap FiveD extruder firmware (and then hack that into working with the custom design!).


Software

While technically programmed as a CupCake right now, we plan to get it running with reprap FiveD firmware once a suitable stepper-driven extruder is constructed for it. Said extruder will probably be printed by the previous extruder (an awesome feat of self-upgrade!).

In programming the board we made a number of changes, though few were permanent.

  • Inverting Z-enable to use a SMD1.2 when one SMD2.3 died.
  • Elongating the bootloader's upload waiting time. Done as the first attempt to increase upload success with hacked cable.
  • Adding a serial print to the extruder's startup - also for uploading timing.
  • Flipping the extruder's motor pins, so that motor #1 has motor #2's pins, and vice versa. This was done because for no known reason, motor driver #1 stopped outputting anything. Turned out the things was not soldered properly, and two pads were not touching.
  • Removing segments of the Arduino servo library, to clean up an error involving __Vector, or something. (Documented that on the FAQ page)

Price-Comparason

Our CupCakeStrap has, to date, cost less than $300. Compared to the CupCake's $750 price, this is pretty significant.

Original CupCake Price Breakdown:

The makerbot's $750 base price is just for:

  • laser-cut plywood and laser-cut plastic = $200
  • 3 NEMA 17 stepper motors and one big gearmotor = $75
  • Nichrome wire, PTFE tube, and a milled barrel and nozzle ~ $30
  • The reprap-derived electronics for controlling it. = $200
  • Nuts, bolts, bearings, pulleys, metal rods and brushings and assorted metal parts, including some magnets ~ $250
  • 1lb of ABS ~ $20
  • Belts = $???
  • M3 and M8 Allen keys = $???

You should note that those prices are what you would pay Makerbot for the individual items (as of march 31st), and do not properly represent their market value. It also totals more than $750.

The "deluxe" version adds $200 for the following:

  • Some more laser cut plastic
  • An ATX powersupply (like in a desktop computer)
  • A USB to TTL cable to interface with it
  • The cables that you need to connect the machine up it its own parts
  • 5lbs more ABS
  • Hex keys, wrenches, and some metal parts
  • An SD card.

(Prices attached only where I could determine their actual cost)

Now, that's a respectable list, and probably worth every penny to someone who does not already have any of those items. However, if you are in a position to use or borrow any of those things, the price becomes a lot less appetizing. Thus, it is a good idea to treat the machine as a RepStrap, and not worry about building an exact clone of the Master CupCake in whose likeness all other CupCakes are forged.

CupCakeStrap Price Breakdown

The CupCakeStrap was built using a lot of scavenged parts, things that were laying around, and a huge quantity of freely available acrylic sheeting. This was especially useful as it meant we could simply laser cut a new part whenever a measurement was wrong. For example, we now have three complete sets of XY stage plastic and about a million failed pulleys.

  • Laser-Cut plywood and acrylic = $0
  • Belts = $0 (from scrapped printer)
  • PSU = $0 (from scrapped computer)
  • 3 NEMA 17 stepper motors and one big gearmotor = $35 (Ebay and a free gearmotor)
  • Nichrome wire, PTFE tube, and a milled barrel and nozzle ~ $30
  • Nuts, bolts, bearings, metal rods and brushings and assorted metal parts ~ $100
  • RepRap Gen-3 PCBs ~ $20
  • Electronics Components ~ $120
Note: One of the stepper boards exploded in construction, so we have replaced them with the Techzone version. This is not counted in the price, because "it should have worked"
  • A USB to TTL cable to interface with it = $3 (Nokia phone cable, bought from Ebay and hacked)
  • A USB cable that actually works = $25 (Bought from the Metrix Create Space when cable #1 stopped working)
  • A 32MB SD card. = $0 Found one laying around, and we plan to simply hardwire it on.

Total ~ $278 This is a pretty rough estimate, pulled from my head. Probably less than this, but unsure.

Related Projects

The Original Makerbot CupCake CNC and the RepRap concept RepStrap.

Design Files for CupCakeStrap

Essentially, these are modified Makerbot CupCake design files, with extra bits added and some assorted parts removed. If I could go back and re-do the machine, I would. Sadly, our supplies of time are too low for that right now.

Downloads

Incoming... Slowly. Files may or may not be actually useful.