Articulated arm
A simple experiment such as for beam deflection can pose a number of challenges if you require it to move around or to have it deflect at a particular angle. This article discusses about an articulated arm capable of moving along 3 spatial axis and capable of rotation about those as well. The setup was designed to hold a right angle prism to deflect a beam towards a model at a specific angle and location on the model for experiments. The parts are designed capable of being 3D printed in place with threads. Some of the assembly components are to be 3D printed as 1 part.
This article will discuss about the basic design considerations for the arm with possible changes to improve them. The design files for the same will be uploaded below for use and modification.
The concept
The assembly is expected to be mounted on a wind tunnel with preexisting mounting bolts extended from the top of the tunnel. Figure 1 shows the assembly with different parts marked. The assembly will be mounted over those and secured in place with nuts. The final mount base and holding rods are mounted using 2 extension arms and a ball and socket joint to allow for rotation about the 3 spacial axis. This can be secured in place using a lock screw. The prism will be mounted in the seating rods and secured in place with a nut. The nut could be adjusted to allow for the rotation of the rods and the prism.
The assembly is completely manual and has no gradations. These can be included to have a more precise control over the attitude of the same.
Assembly components
The different components of the assembly are discussed as parts giving brief idea about the design, manufacturing and other details. The exploded view in figure 2 points to the relevant parts for discussion below.
Base Plate
The base plate is designed to be mounted with 2 flat faces which could be secured over a mounting bolt and against a perpendicular wall. The design is made to allow sliding of the plate to adjust the location in 1 direction. The central boss is the mounting location for the extension arm to be secured using an M16 nut and bolt. A wing nut is preferred as it can allow for easy adjustment while rotating the assembly.
This part is then reinforced with metal welding rods and 2 part epoxy adhesive to improve structural strength and prevent de-lamination. The final part with reinforced bars is shown below in figure 3. The orientation shown in figure 2 can be used as the 3D printing orientation. For reinforcing the part, the rods should be placed vertically or perpendicular to layering (Z) direction.
Extension Arm
The extension arms are used to provide required height with capability of linear movement and rotation about the mounting points. It is a simple section used to hold the mount arm in place. The same can be printed sideways with about 50% infill (have tested down till 35% without much concerns). Figure 4 shows the model in the printing orientation. and figure 3 shows the final printed part attached to the base plate.
Mount arm
Figure 5 shows the mount arm. This is a major part of the assembly which holds the mount base and offers structural support for locking the mount base and locks it in the required orientation. The lock nut and cap cover are assembled to allow for larger surface contact area to lock the mount base in place. The mount arm is suggested to be printed with the location for mounting the mount base flat on the build table.
Note: cap cover is not critical and assembly would still work fine without it. It just increases the area of contact for a more secure locking.
Reinforcing can be carried out to improve rigidity of the parts as shown in figure 6.
Mount base
Mount base is printed with the threaded attachment as a singe assembly. The ball is allowed to fit inside the mount arm and threaded attachment secures it in place allowing it to rotate and revolve. The ball can be locked in place using the lock nut inserted in the mount arm. There is a strip cutout in the front end of the part where a thin steel or iron strip can be attached to allow for magnets to stick to and help with assembly of width adjustment arms. These are secured with bolts at the required location and spacing set using the channels provided.
The part model is shown in figure 8 and figure 9 shows the printed model assembled with mount arm.
Width adjustment arm
This is shown in figure 10 and is suggested to be printed upright. There are slots for mounting rectangular magnets and threaded M6 holes for bolt attachment for securing them in place. The arms have a channel for adjustment of the spacing using an M10 bolt and nut assembly and a mounting hole for assembling the prism seating rod.
Prism seating rod
This is printed standing vertically to make sure threads come out well. These are designed to allow for a right angle prism to fit in the slot. A nut is used to tighten these to the base of the width adjustment arm. This nut can be used to fix or loosen the rod to allow for rotation. Figure 13 shows the model of the prism seating rod and figure 14 shows the printed part with reinforcements.
Final assembly
The complete setup is assembled as shown in figure ***. A simple test with a laser is carried out to point it at a given location using an optical quality prism in prism seating arm.
While manufacturing, the tolerances of the printer should be taken into account and final model adjusted accordingly. The parts printed had to be sanded lightly before assembly as the for assembly, larger clearances were required.
Several improvements to the design can be carried out and incorporated into the model. I would appreciate if any such suggestions can be provided or improved designs generated for a similar application. The files are given in the link below.
https://drive.google.com/drive/folders/18ffZZ5LuZAdVUoG1aGj-Vc1RcNYISEgL?usp=sharing