A Porter-Cable Dual-Action "buffer" has about an 8MM stroke or, the diameter of the oscillation. A Rupes bigfoot like you have has a 15MM stroke. It`s almost twice as big, meaning the circular path from the oscillation is much longer. Just because the Rupes oscillated "slower" in number does not mean it covers LESS distance than the PC-DA. One of the "problems" of DA`s is the lack of forced rotation when pressure is put on the buffer; IE, it stalls or the rotational stroke from the oscillation is reduced because of the lack of power of the motor AND the design of the oscillation motion. Factor in the size of the pad as well, and you have other issues a well. I use only 3" pads on a PC-DA to overcome this because the radius of a 6" pad at the edge will travel much faster and generate more heat at the edge, BUT it will deflect (bend) more. So you loose some of the mechanical advantage from a larger pad transferring the torque due to deflection, and also requires much more motor power to overcome as you press harder and will "stall out" easier. The disadvantage is a smaller pad covers less area and takes more time to polish the same area as a 6" pad, but with "better" results.
Think of it this way: if you are trying to lift 100 lbs, which is easier to do: Lifting close to your body OR with your arms straight out? Its MUCH easier to lift close to you because of the physical property called moment arm torque (no pun intended). The further out a weight is, the more torque is required to move it. Torque in pound-feet is the measurement for power. Electrical motor power is in Amps. Everyone associates horsepower with power, and technically, this is not true. Diesel engines are good examples. They generate small horsepower ratings, BUT output large amounts of torque due to the very long stroke of the connecting rod within the engine and the high compression ratio associated diesel designs compared to conventional gasoline-powered engines of the similar size or displacement. They will not rev very high, BUT their output of power is at a lower RPM, again due to the longer stroke of the piston connecting rod. Sorry for the mechanical physics lesson, but it is not well understood. Our resident detailing physics and mathematics professor, Kevin Brown, has a much better explanation of this subject matter and his applied science is used in some of the detailing products he has developed and sold, along with some of his methodologies. He is living proof that there is a "rocket science" to detailing , but most of us just do not understand it.
As an extension of this idea, this is one of the reasons Flex came out with gear-driven head/backing plate of the 3401 VRG. The gear drive is more "direct" and transfers more of the torque to the head and hence, to the pad. The drawback in this design is the vibration it produces and the resulting user-fatigue it induces, which is another reason some like using the new long-throw dual-action buffers (Rupes Bigfoots, Griots Garage BOSS, and host of reversed-engineered/imitator producers sold under a variety of nameplates coming to market) that have seem to overcome or mitigate this vibration problem, yet still produce the necessary motion and power to produce rotary-like polishing results.
