Video is not the best format in which to present some information so I wrote a companion PDF file which can be viewed and/or downloaded from here: s3-us-west-1.amazonaws.com/hmt-forum/tony_foale_hardness_tester.pdf this also gives a permanent record to keep. Also there is additional information available here: www.homemadetools.net/forum/everyone-needs-hardness-tester-83780#post175021
Hi Tony, This is really interesting and I think it would be a great addition to any workshop as so many don't actually know that level of hardness they are working with... I am off to watch part two now.... Take care. Paul,,
Hi Tony, would using a transducer (piezo, or microphone) integrated into the base of the tube to detect and time the bounce be a simpler design with high accuracy?
It was possible to use only one optocoupler. Calculate the shading time of the ball of this optocoupler. The first time during the fall, the second time during the rebound.
So, making the ratio from incidence and rebound speed is a ratio bitween cinetic energies (taking the measurement really closed to the impact point makes drag losses irrelevants) . It's like if you are calculating the efficiency of the material in not absorbing energy. If I understand it right perfectly rigid material will have a ratio=1...and a jelly material a ratio=0. Is it correct?
I have already answered this same question for you on LinkedIn. The energy ratio is not the same as the velocity ratio, it is the square of the velocity ratio. A ratio of 1 is infinitely hard material, a ratio of 0 means very little but could be considered to signify zero hardness or "dead" material like sand. What does zero hardness mean? Zero hardness will not stop the ball, which will continue accelerating and go straight through. So the concept of zero hardness is a nonsense.
Another solution could be using an ultrasound (car parking) sensor on the top of the tube. There are sensors with 0.5m of range really cheap and easy to use.
Yes the price is right, the range is plenty but you have not mentioned resolution nor accuracy. I suggest that you think about the wavelength of the ultrasound.
Thinking again in what I wrote, I think a ratio = 1 is impossible to obtain because of the "softness" of the ball. For materials harder than the testing ball the results will be not trustable.
Yes a ratio of one is infinite hardness and such material has yet to be found. As long as measurements are repeatable and consistent they can be trusted. The ball characteristics are part of the whole system response but that is no reason not to trust the results. Consider a tennis ball, very soft. Drop it on concrete and it bounces high, drop it on dirt and it bounces less. Then you have a tennis ball hardness scale. As I pointed out hardness is a number dependent on your testing machine.
@@4623620 I got my first, an R60, around 60 years ago. Here is a link to the last special one that I built motochassis.com/wp-content/uploads/2018/06/Milan2.jpg More here motochassis.com/photos/My%20QL/
