Todd, you know I respect your opinion. You are one of those people whose knowledge, opinion, practice and results I admire. That said, I'm pretty simple minded and while I'm no engineer have a good understanding of most things mechanical. So... forgive me if these comments run counter to yours as I'm not trying to be confrontational. I just feel that the free wheeling test assumes too much
My purpose originally in this thread was to explain to you why the pad balance appeared off on the RUPES BigFoot, a tool that is well reputed for it's amazing balance given the ground-breaking stroke lengths the engineers were able to pioneer. The reason for the wobble was because the tall pad was not warmed up and had been resting on the edge. This behavior is certainly not par for anybody who uses the RUPES' system.
I don't believe that spinning freely in the air is an accurate predictor of how the machine will work under an actual load.
I agree and disagree. When it comes to predicting the vibration inherent to the system, I have been told by many mechanical engineers including the team at RUPES, the product lead engineer of RUPES, and the former owner of Cyclo (a mechanical engineer from Harvard) that the most accurate measurement of system vibration is in free air. When it comes to the total experience, vibration is just one part of it (although very valuable part).
There are far too many other factors that help to determine whether the machine operates smoothly under a load, not simply the pad or a pad weighted with polish.
I am not sure if I am just not being clear when I attempted to differentiate between system vibration and user experience, and am growing frustrated at my own inability to explain this clearly.
Yes, there are many factors that add into the tool operating "smoothly." The smooth feel of the tool is something user will experience and thus I have attempted to separate this from system vibration by calling it the user experience. The particular pad's ability to absorb frequency (vibration), load, panel type, expectation, will all effect what the user feels. Even slight differences in nerve allocation and type will have an impact as well are all calibrated differently.
However, there when testing system vibration and the accuracy of the counter weight's ability to cancel out vibration on both the x and y axis, the best test is to operate the tool in free air.
It is much more difficult to make the system operate with near-zero vibration in free air than it is when the tool is enjoying the dampening benefits of a foam pad. With orbital tools there is a direct correlation between the two, although as you noted below, many other factors play into what the user experiences.
I further agree with everybody who has stated that comparisons should be done with the tool on the paint, in real-world conditions. After all the user is going to be concerned with the user experience. The engineers and tool manufacturers are going to be more focused on things like tool and system vibration. I am only attempting to use what I have learned to draw the parallel between the two.
The motor itself, gear alignment and depth of engagement, bearings and their side or end load, tolerances and clearances that change under heat and pressure, the weight of the pad etc are all factors to be considered. These can all come into to play under real world use conditions. The way gears mesh under a load will always be somewhat different than when free wheeling.
Agreed.
While the machine may operate smoothly in the air, I do not believe this is the sole or necessarily the best indicator of how it will perform while in use.
Again, I hope it is clear that I agree (for the most part). Placing load on the tool, heating up various parts (which expand at different rates), etc is all going to play a valuable role in how the tool operates. This is why I have attempted to clarify my differentiation between user experience (smooth running in the the real world) and vibration (load forces on the tool as a factor of imbalance in the rotating assembly ).
I do however believe it's a good place to start. Yeah, my 2 cents are probably only worth .5 cents.
Stepping down from my soap box.
According to the engineers that I have had exhausting conversations with in an attempt to better my education and understanding of such principles, it absolutely the best place to start for a number of reasons.
However, at this point I have done my absolute best to explain what has been explained to me and if I have failed, then I apologize sincerely. I don't want to take this thread any further off topic and take away from the fun and informative video that the Autopia crew filmed.
And I never take yours (or anybodies) comments as confrontational, even if we disagree or if it highlights something that I need to improve my explanations of. I appreciate the conversation and challenges, but past this post, I feel it becomes disrespectful continue to beat a dead horse to the crew who runs this forum.
