In this test, 10 pounds were added to TrotBot with 3 versions of feet:
1. feet with heel and toe linkages
2. feet with only heel linkage
3. feet without heels or toes. As can be seen in the video, TrotBots without heels and toes should be built in a 12 leg version to handle heavy loads.
Also, we added 10 pounds to a toe-less TrotBot that used LEGO's plastic axles, but its bumpier gait required more torque than the plastic axles could handle. Those axles twisted so much that TrotBot could barely walk, so we replaced them with steel axles before filming this test. We should have included a clip of the plastic axle version to better show how heavy walkers with bumpy gaits may need LEGO's plastic axles replaced with steel axles to handle the torque.
An alternative to adding heel/toe linkages to TrotBot is to build it in a 12-leg version, which results in a similar increase in foot-contact with the ground. However, it's a wider build, so the longer crank/axle system will twist more if LEGO's plastic axles are used. For this reason we usually replace at least the inner leg's plastic axles with steel axles when building 12-legged walkers.