Fall 2012 Jumping Robot Team

Team Members: Scott Allen, Kevin Miller, Travis Brack, Paras Ajay

Goal: Build a small vehicle capable of jumping using a mechanism.

Intro and initial prototype:

This semester, the team members listed above attempted to create a jumping mechanism for a vehicle that is capable of jumping at least a foot off of the ground. We began our analysis by looking at a couple of options of mechanisms: a four bar linkage and a crank-slider linkage. Based on our initial prototypes made out of wood, we determined that it would be more practical to use a four bar mechanism actuated by a torsional spring to provide the quick motion necessary for the jump.

Calculations:

We then performed some basic calculations to determine the link lengths, number of springs and the spring stiffnesses that we would need to perform a jump of 0.5 meters long and 0.25 meters high. From this analysis we determined that we would like to use 4x4 bar mechanisms to power the jumping, powered by some pretty large, stiff springs (we eventually chose McMaster Carr P/N: 9271K118). In addition, we performed some calculations and did some basic design work to determine the preliminary design of the legs. Finally, we designed the cam that would drive the mechanisms and did some basic calculations to determine the necessary torque our motor would need to drive the mechanisms (speed of the cam was not important to us at this point as we only need the mechanism to slip off the cam in order to perform the jump).

The hand calculations described above are included here:

Design Calculations by Hand.pdf

Furthermore, some preliminary, basic structural analysis was performed to assure that the material used would be strong enough to handle the loads it would encounter without failing. These calculations are included in the excel below.

Leg Static Force Analysis and Motor Selection.xlsx

Materials:

Now that we had performed the necessary calculations, we started to accumulate materials to build our final prototype. We decided to build the mechanism out of aluminum due to it's ready availability as well as our teams' familiarity with the material. In addition, it appeared that aluminum would provide the necessary strength with relatively light weight.

We also purchased a mobile platform from makershed.com, the instruction manuals for the car and arduino setup are attached here for convenience.

Mobile Platform Instruction Manual: http://www.dfrobot.com/image/data/ROB0003/ROB03-Instruction%20MannualV2.0.pdf

Make an Arduino-Controlled Robot.PDF

We obtained the DC motor (Polulu 131:1 Metal Gearmotor 37Dx57L mm with 64 CPR Encoder) we needed from Dr. Deshpande's lab: DC Motor.jpg

We used a gear and sprocket gear train to further gear down the motor to provide the necessary torque. We used a 5:1 gear train ratio.

The rest of our parts were those readily on hand in the machine shop or purchased from McMaster Carr.

Planning:

When planning to build our prototype, we created a large solidworks model of our entire planned jumping mechanisms. Due to time and material availability constraints, we had to reduce the number of springs and legs that we wished to build to 2 total 4 bar mechanisms with one torsional spring on each 4 bar mechanism. The Solidworks model is attatched below for convenience.

Final Cad.zip

Building and Test:

Next, we built up a working prototype to test. This prototype required a significant amount of time and effort from everyone on the team and we encountered many difficulties along the way. One of the main difficulties was using set screws to attach the d-shafts to the driving link interacting with the cam and the links on the four bar driven by this d-shaft. We had originally intended to use #2-56 set screws to attach these, but found that we did not have a small enough alan wrench to properly drive these into the holes. As a result, our mechanism slipped and the alignment of the mechanism was off such that it did not properly load the torsional springs. This design flaw could easily be remedied by using flanged attachments with set screws through them to attach to the legs and the d-shaft, and we intend to fix this problem and work on improving this prototype.

Here is a picture of our completed prototype: Prototype.jpg

Finally, we tested the prototype and it jumped! Video below:

Final Video.m4v