NASA CHALLENGE - HANDRAIL CLAMP ASSEMBLY

Last crawled date: 1 year, 11 months ago

HANDRAIL CLAMP ASSEMBLY (HCA) DESCRIPTION
In the design of the handrail clamp, the following points were taken into consideration in their order of importance.
1. Safety
a. Sharp edge human factors were carefully adhered to as per CHAMP requirements with all edges rounded to appropriate radii
b. A rigid connection between the clamp and rail was vital as described under point 2 below.
2. Function & strength
a. It was deemed of paramount importance that the assembly has a positive grip on the rail. This point is interleaved with Safety as sudden slippage or opening of the bracket is considered unsafe for the astronaut. This would be quite easily achieved with a 3 or 4 piece assembly by using cams, as is the case with the ISS current clamp assembly for example.
This design has two parts (see point 3) and this was achieved by a design with spiral cam arrangement explained below. The object was to achieve rigidity of the clamp-rail connection at least to the level of the rail interface strength achievable with the ABS printed part.
3. Mass and form
It was decided to limit the assembly to two printed parts for simplicity of assembly for minimum astronaut time.
The shape envelope of 1” around the rail has been not been exceeded.
The volume of the HCA assembly is 4.45 in³.
Figure 01 shows the HCA assembly just before the lock nut is turned to tighten the grip around the rail.
Figure 02 is a view behind the lock nut.
Figure 03 shows the HCA assembly with the nut in the LOCK position.
Figure 04 shows the L-Track snapped onto the rail and the lock nut prior to clipping onto the spiral ears. The lock nut has corresponding spirals and pulls the ears together during the 90 degree locking turn.
Figures 05 and 06 show the L-Track body and the lock nut disassembled.
Figure 07 shows a detail of the lock nut interface. The spiral surfaces of the ears and lock nut taper out away from the L-Track thereby preventing the lock nut from being pulled off the assembly.
Figure 08 shows a cross sectional view of the HCA assembly through the center of the lock nut.
The z-axis printing of the L-Track is in the rail direction and the lock-nut z-axis is along its axis. There is practically no scaffolding material due to the 45 degree angle printing rule.

The lock nut has a larger hole next to the rail than further away from it. Similarly, the clamp widens away from the rail. This results in a conical fit and the lock nut is snapped on and is free to rotate when it comes against the clamp until it is rotated into a locked position. In other words, the two parts have a conical fit that would require the lock nut to be pulled and snapped off with a force.
This will make sense if one observes the cross-section renderings above where the 1 degree taper can easily be seen.

Both parts comply with the maximum print size of 2.36” x 2.36” x 4.72”.