Motor Mount Optimisation

[Assembly context renders]

Four CAD views of the motor mount bracket. — [Final model]

Early revisions removed material from low-stress regions around the motor face and outer profile. Later revisions reshaped the lower reinforcement, reducing stress concentrations without adding bulk. Thickening the load-carrying region proved more effective than simply adding material.

Motor mount design progression: V0, V1, V3, V4, V5, V6, V7, V8, V9, V10, V11 and V14 stress plots. — [Design progression, V0–V14.]

Motor mount FEA iterations V0, V5, V10 and V14 with their individual stress legends. — [FEA close ups]

Mass fell from 0.494 kg to 0.301 kg, while predicted peak von Mises stress decreased from 113 MPa to 95 MPa and maximum deflection from 0.472 mm to 0.441 mm. These correspond to reductions of 39%, 15.9% and 6.6%. A weighted Part Quality Index (PQI) compared mass, safety factor, stress margin and deflection against the baseline, with mass reduction given the largest weight.

Motor mount optimisation plots across design iterations.

\begin{gathered} \mathrm{PQI}_i=\begin{cases} 0,&\sigma_{\max,i}\geq\sigma_y,\\[6pt] \left(\dfrac{m_0}{m_i}\right)^{0.400} \left(\dfrac{g(SF_i)}{g(SF_0)}\right)^{0.275} \left(\dfrac{1-\sigma_{\max,i}/\sigma_y}{1-\sigma_{\max,0}/\sigma_y}\right)^{0.150} \left(\dfrac{\delta_0}{\delta_i}\right)^{0.175},&\sigma_{\max,i}<\sigma_y. \end{cases}\\[12pt] g(SF)=\dfrac{SF_{\mathrm{target}}}{SF}\exp\!\left(1-\dfrac{SF_{\mathrm{target}}}{SF}\right),\qquad SF_{\mathrm{target}}=1.5 \end{gathered}

PQI is normalised to 1 for the baseline and set to 0 at or above yield. m: mass; SF: safety factor; σmax: peak von Mises stress; σy: yield strength; δ: maximum deflection. Subscripts 0 and i denote the baseline and current revision. The function g(SF) peaks at the target safety factor of 1.5.

Dimensioned motor mount bracket assembly drawing. — [Dimensioned Engineering Drawing]