Proves that there's literally an app to do anything. I'm amazed. Good job!
thank you :)
Show HN: Racketmeter – Measure Badminton String Tension Using Sound Frequency
11–14 of 14 posts
Re: Show HN: Racketmeter – Measure Badminton String Tension Using Sound Frequency
#12It sounds like you've done plenty of experiments and don't need any theory to make this work, but have you looked at the physics/mathematics of the vibrations? Does the frequency you detect correspond to https://en.wikipedia.org/wiki/Vibration_of_a_circular_membra... , for example? I'm guessing that the interlocking strings are best modelled as a membrane rather than individual strings ( https://en.wikipedia.org/wiki…
Ah, the string spacing cancels out, doesn't it? I'd expect the frequency to be proportional to sqrt(t/d)/a, where t is the string tension in Newtons, d is the linear density of the strings in kg/m, and a is the diameter of the racquet head (assuming they're all the same shape and measured in the same way, which probably isn't true, unfortunately).
yeah. Spot on. For the app, I don't take into account the density, but racket head is taken into account. Prominent shapes are oval and isometric, so I have separate co-efficients for those, which were learned using regression.
One challenge that I haven't figured out yet is when 2 different types of strings are used. It seems, some advanced players use different strings at different tensions for the horizontal and vertical strings. Like 32x28lbs or other similar configurations.
Re: Show HN: Racketmeter – Measure Badminton String Tension Using Sound Frequency
#13The Gates company make the Gates Carbon Belt to replace bike chains with a carbon fiber belt (encased in some polymer). My Priority Bicycle 600x has this belt drive, along with matching sprockets and a Pinion C1.12 "transmission", where all gearing/shifting takes place.
To check proper tension, Gates supplies an app [0] that also has you pluck the belt to measure the frequency. For my bike the appropriate tension is at 60Hz. Tension is adjusted by moving the rear axle backward or forward.
[0] https://play.google.com/store/apps/details?id=com.gates.carb...
EDIT: the advantages are ... no fragile derailleur; no chain lube; long belt lifespan; low maintenance
Re: Show HN: Racketmeter – Measure Badminton String Tension Using Sound Frequency
#14Great work, I love this.
I tested it with my recently restrung BG80 at 27lb and it came out with 26.69lb!
One improvement I'd ask for, is in the string thickness selection. I had to go look up the thickness of BG80. It would be cool if you could preload some of the popular strings in there.
Also, the string tension number is good, but I'll get it to a peak and then I'll stop to press the stop recording button and it's dropped back down. It would be nice to have a "Peak tension" or a graph of the tension.
Thanks