Steel is best, Georgi- Aluminum will erode rather quickly because of sand and grit on the tire surface.
Not state of the art but entirely adequate, especially if actuated by plastic lined bicycle cable.
I ran through the numbers before deciding on scrub brakes.
A 500 lb gyro traveling 20 mph has a kinetic energy of 6753 ft-lb. (1/2 mv²)
6753 ft-lb of kinetic energy equals 8.7 BTU.
Steel has a specific heat of 0.12 BTU/degree F/lb. Meaning 0.12 BTU will raise the temperature of 1 lb. of steel by 1ºF.
So, with each scrub brake pad dissipating ½ of the gyro’s kinetic energy and each pad weighing ~ ½ lb., we have 8.7/2 = 4.35 BTU/wheel and since each pad weighs ½ lb, it is (4.35 x 2)/0.12 = 72.5ºF over ambient, pretty warm but not hot enough to melt rubber.
And that’s ignoring the cooling of the pad during the stop via conduction, convection and radiation as well as the braking effort of the rotor.
