Variable Angle Device for Evaluation of Rovers (VADER)

Dr. Robert Ambrose and the RAD Lab at Texas A&M sponsored this capstone project. RAD Lab is a robotics developing novel rover designs for space exploration. Some Rovers they are developing can be seen below in Figure 1 and Figure 2.

With all of these rover concepts, it is important to be able to evaluate their performance in a repeatable and standardized way. It needs to be repeatable by resetting the testbed to the same condition each to ensure experiments produce consistent outcomes. Standardized testing means that the test bed and results can be compared to other rovers (i.e. not using a natural hill open to the elements for testing).  This requires a controlled inclining test environment with a lunar simulant material surface for their rovers.

There are several existing test systems for rovers, such as the NASA SLOPE Lab and the Georgia Tech CRAB Lab. These systems are effective for the organizations that use them but are both incorrect scale for the RAD Lab rovers. Thus the RAD Lab has tasked our team with creating a novel design for an inclining rover testbed specifically for their needs.

To begin to define the goals we first created a requirements checklist. This was made using both the explicit requirements initially presented to us by our sponsor as well as implicit requirements that were discovered through interviewing the sponsor about expectations and desired use cases of the test apparatus. The requirements list can be seen in Table 1 below.

Using the requirements developed above and further input from our sponsor, our team developed a solution neutral problem statement which can be seen below. 

To ensure we were exploring all possible solutions, we performed three different idea-generation methods. Our focus was to identify solutions that not only met the technical requirements for functionality but also a combination of efficiency and simplicity. The methods used were the 6-3-5 method, design by analogy, and research-based idea generation. 

The 6-3-5 method is performed by having six group members each sketch three concepts within five minutes. After the five minutes are over, the concepts are rotated among the group, and each member repeats the 6-3-5 process, generating three new concepts based on the concepts they received. 

Design by analogy involves looking at mechanisms and systems that have analogous functions or working concepts to our problem. This is my personal favorite as it involves creatively looking for similar issues or functions in the world around us, and it is interesting to see how different industries solve similar problems in different ways. 

Research-based idea generation involves searching through publications and patent databases for solutions to similar problems. This is similar to design by analogy, just strictly from patents and academia.

After ideas were generated, the ideas were discussed as a team to select the most promising one. In this step of concept refinement, more in-depth research on the feasibility, capability, and costs of each idea was performed. Additionally, detailed sketches were made for these concepts. 

An example of a refined concept model created for this step can be seen in Figure 3 below.

Finally, once concepts have been refined they need to be evaluated and compared. This was done using several comparison matrices. The ideas were first initially compared using a Pugh Chart, in which each concept is intuitively scored based on chosen selection criteria. Pugh chart is better for a quick estimate of general comparisons but can easily be inconclusive resulting in a tie.

The next method of comparison was much more in-depth; the quantitatively driven team effort selection matrix. This matrix was very similar to a trade study. It involved first selecting quantifiable selection criteria, then evaluating each concept performance for those criteria using engineering calculations and estimations, and then making those scores dimensionless by using interpolation. Each criterion is given a weight by using a system of equations comparing them to each other, and then the dimensionless scores are multiplied by the weights and summed to get the total score for each concept. 

Examples of each selection matrix can be seen below in Table 2 and Table 3.

Being a project with several complex functions to design for, this three step process was completed three times. This section will summarize the extensive documentation that was completed for these steps.

The first function where we generated idea, refined concepts, and selected a concept was inclination method. This was to fulfill the requirements of inclining up to 35 degrees with 1 degree resolution while holding the aggregate an rover payload (calculated as roughly 6000 pounds). The two main categories of concepts for this function were designing and welding a mechanism ourself or purchasing a dump trailer. The Dump trailer was something discovered in design by analogy, and it matched the dimensional and load capacity requirements while also taking far less time to design and build for roughly the same financial cost. The chart in Figure 4 below summarizes the ideas generated with the chosen concept in green.