Open Hybrid Mendel
The Open Hybrid Mendel (or OHM) is a project of the State College Reprap Users Group. It is a Mendel design, which uses both standard Sells Mendel parts, a Prusa Z drive, various redesigns from the community at large, and a number of small design improvements developed in our PSU Reprap class. It is so named due to this hybridization of designs, and obtains the 'Open' designation from the OpenX and OpenY axes it uses. The prototype for the OHM design was Etherdais_Unit_One
Expanding into the realm of the biological, the OHM is the basis for a Mendel-based PCR system, currently designated the RepRap Mullis.
Any Mendel can be broken down into 6 sub-systems, which are somewhat interchangeable between designs:
Frame - The OHM uses Camiel's thin shelled Vertex design, maintaining vertices similar to the Sells design, but using less filament
Y-axis - The OHM uses a modified OpenY, with an optoless belt harness, and a second 90/180 arm in place of the 90/270 arm. This demands two additional bearings, but we find the result is more stable, while retaining the benefits of the OpenY. A modified Sells y-motor bracket is used, which avoids printing an unused endstop holder from the original Sells design. The original Sells y-bar clamps seem well suited for mounting y-axis opto-endstops.
Z-drive system - The OHM uses a Prusa, double motor design for driving the Z axis, avoiding the large prints and continuous belt of the Sells Z-drive design. We still use Sells bar clamps to clamp the smooth rod to the Z-motor mounts, as they are compatable, and look sharp together.
X-Z assembly - Currently, the OHM build uses a standard Sells X-Z assembly, as described here in Mendel_X-axis.
Carriage - The OpenX carriage is the design of choice currently, with modifications to the Undercarriage Bracket and Arm that have been found to reduce side to side wobble and skew. For a list of changes, see the X Carriage section.
Extruder - We are in the process of finding a design which is more compatable with the TechZone steel hot tips we've been using recently, though the current design is a hack of herringbone extruder gears, and GregFrost's hinged wades extruder.
Spool Arm - The OHM uses an "in-house" design to support the PLA spools. See Spool Arm Design.
Download Zip: File:OpenHybridMendel 0.1.zip
Frame and Z Axis Parts
|6||camiel_frame_vertex_6off||Alternative part by Camiel|
|1||y-motor-bracket_1off_mod3-15||Modified by PSU Reprap Collective|
Y Carriage Parts
|1||8mm_Belt_Harness_1off||Open Y by Buback, modified by PSU Reprap Collective|
|2||8mm_Crossbar_Mount_2off||Open Y by Buback|
|2||Arm_90-180_2off||Open Y by Buback|
|1||Arm_210_1off||Open Y by Buback|
|1||OpenY_Undercarriage_Bracket_1off||Open Y by Buback|
X Axis Parts
|4||pla_coupling_nophead-1piece_4off.STL||Alternative part by Nophead|
|1||xaxis-motor-bracket_1off||Alternative part by Rhys-jones|
Two major issues affected the Open-X carriage: carriages occasionally "walk" up off the tracks, and inconsistent spacing of the undercarriage bracket occasionally allowed the extruder to move/twist laterally. Both of these issues were minimized through modifications by user Joe Bartolai. The OpenX Arm was shortened and an offset was added so that the bearing attached to it is centered on the rail. The OpenX undercarriage bracket was also modified by making the angle steeper where the lower bearings contact the rail. Part models will be added soon.
|1||OpenX_Carriage_1off||Open X by Buback|
|1||OpenX_Undercarriage_Bracket_1off||Open X by Buback|
|1||OpenX_Arm_1off||Open X by Buback|
Currently not included in STL zipfile
|1||HerringboneDrivenGear||Alternative part by Rhys-jones|
|1||HerringboneDriveGear||Alternative part by Rhys-jones|
|1||Gregs_accessible_wades_v6||Alternative extruder by Greg-Frost|
|2-5||prusa_modified_endstop_holder_2-5off||Prusa opto holder modified to have a thicker end||No picture yet|
|3||electronics_board_mount_opt||Created by RUG member SethG. Optional|
Quantity of Materials Needed by Subsystem
|Part Name||Frame||Z-Axis||Open Y-Axis||Open X-Axis||X-Carriage||Extruder||Total|
|M3 Cap Screw 20mm||4||-||-||8||-||4||16|
|M3 Cap Screw 25mm||1||8||-||13||2||-||24|
|M4 Cap Screw 16mm||-||4||-||4||-||-||8|
|M4 Cap Screw 20mm||-||1||12||9||14||-||36|
|M4 Cap Screw 40 mm||12||-||8||22||-||2||44|
|M4 Dome Screw 30 mm||-||-||-||-||-||3||3|
|3/16" Fender Washer||8||-||-||8||-||-||16|
|Bearing 8x22x7 mm||-||-||-||-||-||3||3|
|Bearing 4x13x5 mm||4||-||12||4||10||-||30|