Brake Design Challange
Teams: The challenge is to be done in the sponsored project teams. If you are in a team of 2, then you can join another team of 2 or do this challenge separately.
Due Date: Wednesday 3/21 midnight (finals week). Upload documents to TritonEd.
When using simulation tools, validating computational results is of utmost importance. This assignment will develop the skills for using hand analysis to validate and guide computer optimization.
The objective is to maximize the braking torque on a shaft in Newton Meters (Nm), subject to the constraints listed below. The design should be validated with a simulation in Working Model 2D (WM2D), and also estimated by hand analysis. Optimization approaches to consider include:
Angle of brake pad contact
Variable mechanical advantage
Use of braking force to generate more braking force
To submit: digitally upload a PDF of your report, then upload the working model file to TritonEd. Two different uploads, and only one team member needs to submit them.
Brief description of at least 3 designs, including figure, and why you choose this design.
Hand analysis of each design with an estimation of the braking force.
WM2D simulation of each design, subject to constraints below. Briefly describe how you validated that simulation is correct including discussion of accuracy and pause settings (see description of baseline model).
Brief comparison of hand analysis to simulation.
Summary table showing all designs considered.
Grading will be based upon quality of write up, validity of analysis, and 50% will be base upon achieving the highest braking force in a valid WM2D simulation.
Constraints and Guidelines
It is recommended that each team start with the provided Brake Design Baseline file. The constraints are as follows:
The brake must be actuated ON and OFF by the piston force. Accordingly, if the piston force is off, the brake must remain non-active. Once the brake is activated, then the brake must be able to retract by reversing the piston force. Make sure to test this.
The piston can generate a maximum of 94N as determined in the previous piston analysis.
The maximum stroke of the piston is 20mm. This must be confirmed by measuring the point of force application as done on the baseline example.
The shaft has a diameter of 20mm
There must be an unobstructed space of 3mm surrounding the shaft prior to brake application (so the brake does not rub if heating or misalignments occur).
The maximum coefficient of friction between the brake pad and the shaft is 0.3. All parts of the brake that do not touch the shaft, such as internal pivots, do not have friction.
The brake design may not exceed a space of 20cm x 20cm surrounding the shaft as shown with the green rectangle in the baseline example (these rectangles or location of the shaft cannot be moved). The brake mechanism must be in 2D. The piston will be modeled by a force vector, a and there is no need to fit the piston into the 20cm x 20cm space.
For this analysis there is no need to retract the brake, and there is no need to calculate the buckling force of the brake piston, or any moment loads applied onto the piston.
Hand Analysis Example
Hand analysis of 3 brake configurations: a horizontal brake pad, an angled brake pad with counter-clockwise rotation, and an angled brake pad with clockwise rotation in which the braking friction force adds to the braking force. The comparison of the hand analysis and WM2D were as follows:
Horizontal brake pad: Braking torque = 0.283Nm for hand analysis, and 0=0.249Nm in WM2D simulation (12% difference)
Brake pad at 30 degrees with counter-clockwise rotation: Braking torque = 0.278Nm for hand analysis, and 0=0.282Nm in WM2D simulation (1.3% difference)
Brake pad at 30 degrees with clockwise rotation: Braking torque = 0.395Nm for hand analysis, and 0=0.398Nm in WM2D simulation (0.8% difference)
Working Model 2D Resources
Example of surgical shears
Baseline Brake Simulation (click to download file)
The baseline file provided already has the modifications described below. However, these modifications are described below so that you know what model you are working with.
The WM2D geometry is pretty simple;
a shaft with an applied torque.
a rectangular brake pad constrained by a linear slide. Default standard material settings are used, with a modification to set elasticity to zero to eliminate bouncing during contact with the shaft.
a force that presses the brake pad onto the shaft
For graphical purposes there are:
anchored rectangles that show the allowed 20cm x 20cm mechanism space.
an anchored outline showing 3mm surrounding the shaft. So that this outline does not interfere with the simulation it needs to be set to "do not collide" with the brake pad and the shaft. This is done by selecting the outline and brake pad (hold shift key down), then select menu: Object => Do Not Collide. The same procedure is implemented for the outline and the shaft.
A number of settings have been created so that the braking forces can be measured automatically:
Gravity is turned off: World => Gravity => None
The accuracy has been adjusted as follows:
World => Accuracy => Accurate
Change Overlap Error to: 0.0001 m (0.1 mm)
The torque on the shaft has been set:
It only become active after a Torque Delay in seconds, so that the shaft does not start spinning before the brake becomes engaged. A text input box allows setting the Torque Delay.
The torque increase as time increases, so that we can find the torque at which the shaft begins to rotate (this is the maximum braking torque). A Torque Multiplier allows the torque to increase faster as a function of time. This multiplier is initially set to 1, but you may want to increase it if your braking forces get high. Also a directional multiplier of +/- is included, so one can change the direction of applied torque.
Pause control is set so that the simulation stops as soon as the shaft begins to move.
The pause criteria is set as: Abs((Body.p.r*0.017) )> 1
Body 1 is the shaft, and p.r designates "position" and rotation", the 0.017 converts to degrees and > 1 degree is a threshold for motion.
Note, using position as a criteria for pausing is more reliable than using velocity, since a velocity spike can occur when the brake pad impacts the shaft leading to a premature pause.
Measurements are shown of:
Shaft torque to illustrate maximum braking force.
Motion of point of force application, so that one can confirm that the maximum piston travel is not exceeded (you will need to compare the x and y initial position to final position)
Time of simulation. This is important if you are using Virtual Labs and have a pause control set to end at a certain time. You need to check that the simulation stopped when the shaft began to rotate, not when the pause control kicked in.