Bonsai RepStrap

From RepRap
Revision as of 12:07, 13 May 2010 by Sci (talk | contribs) (Removed broken forum embedding - Can't get it to display)
Jump to: navigation, search

This page is a development stub. Please enhance this page by adding information, cad files, nice big images, and well structured data!

Crystal Clear action run.png
The Bonsai Repstrap

Release status: Concept

No image available.png
Description
Small/portable Mendel-inspired 3D printer
License
Author
Contributors
Based-on
Categories
CAD Models
None
External Link


Background

Sci, browsing ebay on Feb 26th, 2010:
  "Hmm.. 2000 surplus stepper motors.. that must be useful for something."

The Bonsai RepStrap is a development by Peter "Sci" Turpin. It aims to be a small, lightweight 3D printer that can be used for making the parts for larger full RepRaps.

An early concern for making the printer easy to ship without having to substantially dismantle it and subsequently require total recalibration has developed into a repeatable folding-frame concept. Combined with the low-power motors, this should have the added bonus of making this the first readily portable 3D printer, as well as the initial intent of making it small and affordable.

The currently intended sale price for a complete working machine is about the £200 mark, though this will probably be revised as development progresses and the full range of costs is determined.

Current elements

Motors

Model SMS35-4815-C
Manufacturer Fuji Electrochemical Co.
Type 6-wire Unipolar, twin-can
Voltage 24v
Coil Ω 120Ω
Step angle 7.5°/step*
Diameter 34mm*
Thickness 15mm*
Shaft length 7mm*
Shaft diameter 2mm*
Torque - Wave drive 133.4g/cm*
Torque - Full step 211.7g/cm*
Mount spacing 42mm*

*Calculated from sample motor testing. No data-sheets are available due to the age of the stock and manufacturer change of ownership.

Connector pinout (0.1" pitch):

1 (Blue) Coil A
2 (Yellow) Coil C
3 (Green) Common for 1+2
4 (Green) Common for 5+6
5 (Red) Coil B
6 (White) Coil D

A total of 2053 motors were in the lot. 1672 regular, 381 with 12-tooth plastic gear pressed onto shaft.

Development

Currently able to run on basic L297/Darlington circuit, though must implement current limiting due to rapid motor heating.

Drive

Expected to use a wire-drive using 0.7mm nylon-coated steel cable wrapped around a small capstan. Z-axis will likely need a secondary guide cable to keep the axis square, due to the off-centre requirement for it's drive motor.

Frame

Starting with a Mendel style frame, to reduce weight and complexity the separate axis runners were removed from the design and instead opted to sheath the parallel frame studding in a push-fit stainless or aluminium tube to allow them to act as runners. To keep the frame square, it will likely use a laser or CNC cut plastic base-plate.

Development

Originally the prototype was going to use aluminium tube, but the metals supplier was out of anything with an accurate 8mm ID, so stainless was bought.

Folding mechanism

As it would be a low-mechanical-stress design, half of the A-frame is removed and the Z-axis doubles as the upright support. Here is a brief video clip of prototype folding mechanism:

<videoflash>sbhP2Xw5OpM</videoflash>

The diagonal support will need a quick-release but adjustable clamp to allow it to be rapidly folded and re-set. No such clamp currently appears to exist, so a printable variation of a Cord Lock with an integral half-nut is being designed.

Plastruder

To keep mass of the extruder head down, the feed motor will deliver filament via a Borden cable from the printer base. To simplify mounting, the heater assembly will be using a rectangular PTFE block which can be simply have mounting bolts passed through. The heater will use an aluminium block with heater resistor, similar to that used by the Hydraraptor.

Electronics

Control

Prototype using a direct PC-Parallel-Port connection. Likely that a Sanguino or other Arduino-varient will be used. Investigating using processor to directly generate stepper sequencing and remove dedicated stepper ICs from the design.

Links

Dreamwidth blog (subject tag) RepRap Forum thread