Jim is standing well off to the side when the statically balanced crank is spinning fast and shaking about.
The fellow who dynamically balanced my 1360 crank and the 920 crank uses a Hines Dynamic Balancer which has the same open v blocks as in Jim's machine. I don't know what rpm he takes the crank up to, but my 1360 went from nearly un ridable to a very pleasant 8 hour bike just with the dynamic balance vs static balance.
My take on it is that if there is very little rocking couple, the static balance will get a good result. If there is a lot of rocking couple, the static balance is about useless.
The problem is, you don't know whether the rocking couple exists unless you put the crank on a Dynamic balancer.
As far as the shaking forces in the first video, my understanding is that the machine measures all of them including uplift and then tells you exactly where to drill or add weight in order to cancel those forces. The fellow who dynamically balanced my crank starts out with very low speed, maybe 25 or 30 rpm. He starts correcting the rocking couple while working toward or maintain the desired BF. By the time he gets the crank up to high rpm it is running very smoothly, like the dynamically balanced crank in Jim's second video.
Jim's first video is to demonstrate where the problem is with static balancing, so it was necessary to get it up to speed to show how wonky it really is, even with a perfect static balance.
I recall when he first showed that video, the safety police came out in large numbers.
Glen
