Optimised Design of a Helical Compression Spring for a UGV Coil-Over Shock Absorber
Assignment Brief
Use MATLAB “fminsearch” to design a helical compression spring for a coil-over shock absorber in a small unmanned ground vehicle (UGV) based on the following specifications. You must attach hard copy of your code and MATLAB output. minimum weight must fit over 0.57 inch DIA shock body minimum working force Fw = 15 lbf at working length Lw = 1.5 inch minimum factor of safety NFS of 1.0 to prevent yield at shut length Ls (fully compressed) free length Lf = 3.0 inch, total number of coils Nt = 14 round steel music wire or round zinc-plated steel music wire squared (closed) ends or squared-and-ground ends.
Current design – Nt = 14, Lf = 3.0 in, OD = 0.80 in, d = 0.081 in, w = 0.046 lbf, NFS = 1.30 2) Select a spring that most closely matches your optimal design from McMaster-Carr. Optimal design McMaster-Carr wire diameter d [in] ____________________ ____________________ coil OD [in] ____________________ ____________________ total number of coils Nt 14 ____________________ free length Lf [in] 3.0 ____________________ weight [lbf] ____________________ ____________________ coil ID [in] ____________________ ____________________ spring rate k [lbf/in] ____________________ ____________________ force at Lw [lbf] ____________________ ____________________ shut length Ls [in] ____________________ ____________________ factor of safety NFS at Ls ____________________ ____________________ McMaster-Carr part number ____________________ cost each ____________________ 3) Will your optimal spring buckle at Lw? yes no Show your work! Extra credit – Explore the sensitivity of your design to number of coils and free length.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ % t_fminsearch.m - test fminsearch % HJSIII, 14.10.16 % initial guess x_start = [ 1 1 ]`; % call [ x_solution, min_val ] = fminsearch( `biquad`, x_start ) % bottom of t_fminsearch +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ function z = biquad( x ) % biquadratic test function for fminsearch % HJSIII, 14.10.16 % minimum = 3 at x(1)=2 and x(2)=5 z = ( x(1)^2 - 4*x(1) + 4 ) + ( x(2)^2 - 10*x(2) + 25 ) + 3; % penalty function to provide inequality constraint % constrained minimum = 3.8 at x(1)=2.4 and x(2)=4.2 %t = 0.5 * x(1) + 3; %if x(2) > t, % z = z + 100; %end % bottom of biquad +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ » t_fminsearch x_solution = 2.0000 5.0000 min_val = 3.0000
