�
����������� Following
completion of the 2000-2001 design, two flaws were discovered but could not be
addressed before the completion of the academic year.� First, the belt driving the shoulder twist
pulley was found to slip.� It appeared
that the Neoprene belt stretched under the stress of the pulley system.� Second, binding occurred between the elbow gearing due to a lack of thrust support for both sides
of the worm.� Additionally, the two-part
aluminum elbow shaft was too weak to support the forearm.� The aluminum yielded from the stress of the
steel pin securing the elbow worm gear to the shaft.
����������� To
eliminate slipping at the shoulder twist pulley, a stranded or V-shaped belt
should replace the Neoprene belt.� Because
a stranded or V-shaped belt is less likely to stretch under tension, the belt
will maintain high pressure around the pulley, eliminating slip.
����������� To
eliminate binding, components for the elbow were redesigned.� The steel drive shaft for the screwdriver motor
is elongated to enable placing a 0.434-inch stainless steel thrust bearing at
the free end.� A small aluminum block
houses the thrust bearing and mounts within the lower arm tubing.� The elbow motor is repositioned to
accommodate the additional thrust bearing.�
See Figure AD.1 for the cutaway view of the elbow joint incorporating
the thrust bearing.
����������� Manufacturing
the two-part elbow shaft design with steel is not possible because steel cannot
be machined to the tolerances required for the design.� Therefore, the two-part elbow shaft is
replaced with a solid 0.25-inch diameter shaft.�
The repositioned motor requires the elbow shaft and worm gear to be
offset within the lower arm tube.�
Finally, the elbow brackets were revised to still permit the forearm
tubing to rest upon the lower arm tubing in the home position.� Please see Figure AD.2 for the final elbow
redesign.
While the design changes have not been
evaluated for their feasibility, experimental performance during the final
presentation for the 2000-2001 arm indicates that the modifications will
adequately support the forearm.� Since
bearing support and the resizing of the elbow brackets were the only major
modifications, the modifications will eliminate the flaws and produce a
successful design.
Table AD.1 � Elbow Revision
Bill of Materials
ELBOW REVISION BILL OF
MATERIALS
|
Description |
Part Number |
Vendor |
Qty. |
|
|
ET-02-5 |
PIC Design |
1 |