Back story: MOSTLY PRINTED PICKLEBALL BAT TEST RIG
The son of a friend is an apparently well known manufacturer of Pickle Ball bats and accessories. He (the father) and I have spent many happy hours playing with materials, shapes, cores and surfacing - and general prototyping of bats. We experiment with combinations of glues and a wild variety of cores, make templates and jigs and whatever else we think is needed, thickness the cores, and then he goes home to play, building the actual prototypes.
Then they are tested by a few pro players, and then put in the “Maybe good for production” pile, and on we go.
Our “Problem”
We’d like to build a test rig to determine durability of the cores - I think using a weighted lever and a ball, that can repeatedly strike somewhere in the bat’s sweet spot. In principle a lever on a cam that runs backwards and forwards on another cam that raises and lowers the gadget will probably work.
It will take a bit of nutting out and if anyone has some ideas I’m happy to listen (and yes I know the top cam as drawn will not work), but the bits I’d love some suggestions/help on in particular are:
What sort of motor should we use.
How do we rig a counter (I presume something against the lower cam would work, but I don’t know what “something” is)
How do we rig a simple reversing setup? I’m sure theres’ a Pi/Arduino answer in there, which even if you explain in words of single syllables I will barely understand, but I’ll try!
Or should we just ask the factory in China to work it out?
Well I did have a thought.
For some reason I see a lot of people using wiper blade motors for a lot of stuff, especially stuff tied to robotics.
Maybe because of the 12v power requirement, or longevity of the motors. Maybe because of the ability to find them readily available in a junk yard. Not sure.
But depending on the speed needed for the rotation……
Wipers are interesting because they have a pretty clever mechanism to convert a constant rotation into an oscillating rotation:
The motors would be fine too. But if you built that linkage, you’d be able to use any universal motor.
One issue is that at the end of the travel, it is moving the slowest. So you need to “punch through” the mechanism to hit it with any force.
Honestly, a simpler solution would be to just give it a lot of space, let the ball arm swing 360 degrees and put the bat on a spring to let it get out of the way after it gets hit.
Also, the bats will probably last a long time in the hands of players. So they will last a really long time if the test bench can’t hit as hard as a human. Ideally, it would break the bat many times faster/harder than a player so you can get to the answer faster.
That sounds a bit dangerous. Make sure you consider safety and don’t trust procedures to keep people from getting clobbered. If you can avoid software, it will make it much easier to “prove” it is safe.
And my other thought is that you’ll have to build the test rig to be tough if you don’t want it to break. It is trying to do damage and every action has an equal and opposite reaction. It should be at least an order of magnitude harder to break than the bats.
Thank you all so far! For now we are trying to test for delamination rather than “breaking point” - the core materials we are playing with are “secret” but crushable foams, so it’s a question of how many matches the racket (thanks @pony1023 ) will last. Current core materials are PVC honeycomb, and rackets can be “played in” and then discarded (used for practice) after their peak rebound time has expired. We think this is mostly psychological, but we are an 80 year old beginner and yours truly who doesn’t play at all, so we’d like to measure that eventually.
But for now we’ll be content to just measure the point at which delamination occurs. If I was geeky enough I reckon I could rig up a recording device which could do that by sound! First though - lets see what the mechanical machine looks like.
The acoustic measurement may actually be something to key on. Track the impact frequency vs time and note when it shifts significantly because that would indicate something has changed.
I imagine the trick in all this fatigue and impact testing is to keep the bat light and still rigid enough to produce the desired bounce. Sounds like a good engineering problem.
On areospace test fixtures, we put multiple three axis accelerometers on the test article and then look for changes in the dynamic response of the test article. Yes, this does reveal a lot about the failure modes of the object.
We also compare the response against the solid model as you can also learn a lot about process related failures where something you do in manufacturing has unexpected ways it compromises the as-built item. We learn a lot about how not to build things from such testing.
