[HN Gopher] Show HN: Racketmeter - Measure Badminton String Tens...
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Show HN: Racketmeter - Measure Badminton String Tension Using Sound
Frequency
Racketmeter lets badminton players measure string tension using the
sound frequency produced when tapping the racket strings. It's 100%
free, works in your browser on mobile and desktop, and requires no
sign-up or installation. I built it to solve a personal problem. I
started playing badminton regularly in 2016 and quickly learned
that players often ask stringers to string rackets at specific
tensions (like 22 or 26 lbs). But after a few stringing jobs, I
began to feel like the tension was inconsistent. Other players told
me they just tap the strings and go by ear where "sharper sound
meant higher tension." One day while tuning my guitar, I could see
exact sound frequencies on my tuner app. That's when it clicked. It
should be possible to build a tuner for badminton strings as well!
I searched online and found some tension-frequency data shared by
professional stringers, but it wasn't clean or comprehensive. So I
visited 5 or 6 local stringers, gave them a frequency measuring
app, and asked them to record racket head size, string thickness,
tension, and sound frequency for each job. Some asked for a small
payment, but most helped for free. Within a week, I had over 200
solid data points. I trained a simple regression model using that
data and validated it with newly strung rackets. It turned out to
be surprisingly accurate. I shared it with friends and fellow
players, and it started to spread in badminton forums. There was
another app that launched a few months later with big celebrity
endorsements, but it was less accurate, harder to use, and required
in-app purchases. Mine wasn't built to compete, but it ended up
being more useful. I originally released it as a mobile app, but
constant changes in Google Play policies kept taking it down. So I
rebuilt it as a simple browser-based tool. Would love feedback,
suggestions for improvements, or ideas on how to sustain it without
cluttering it with ads or paywalls. Let me know what you think.
Author : zhacker
Score : 32 points
Date : 2025-05-18 17:08 UTC (5 hours ago)
(HTM) web link (www.racketmeter.com)
(TXT) w3m dump (www.racketmeter.com)
| fock wrote:
| While I don't play Badminton (and so can't test with a racket on
| hand) this seems very cool! I also thought about something
| similar for judging bikewheel spoke tension - I guess I have to
| research this a bit more now.
|
| As for monetization: I personally don't have problems with static
| ads served from your domain. Find some celebrity or brand and ask
| them if they want to have you serve their banner.
| zhacker wrote:
| if spokes come in standard guages, it should work for
| bikewheels as well. There may be some differences due to the
| bike rim material, but in case of badminton, I found out that
| frame material could be ignored safely.
| cr125rider wrote:
| Great solution to a real problem. Very "hacker" of you - nice
| job!
| zhacker wrote:
| haha, thanks :D
| HyprMusic wrote:
| Very useful. I just tried it with my spare racquet, and it seems
| about right. I have always wondered if my main racquet has lost
| tension, so it'll be really useful for that.
|
| For making money, I'd suggest reaching out to professional re-
| stringers and asking if they want to advertise (once you have
| some nice analytics to brag about). Maybe even localise them
| based on geolocation data so you can have more re-stringers
| without cluttering it up. It's a value-add to your users so
| everyone should be happy.
|
| You could probably even reach out to some YouTubers (I personally
| like BadmintonInsight). Since it's free, I would imagine some of
| them would do a video on it just to help their viewers.
| zhacker wrote:
| Finding stringers nearby is really cool idea. Yeah,
| BadmintonInsight is a really good channel. I'll try reaching
| out.
| bloak wrote:
| It 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/String_vibration) but the racquet
| head isn't circular, so it's a bit beyond my level of maths to do
| that properly.
|
| I suppose that to do the maths we'd need to know the spacing of
| the strings and the mass per unit length of the strings. (And the
| dimensions of the racquet head, of course, but that must be easy
| to look up.)
|
| Also, would this work just as well for tennis and squash
| racquets?
|
| EDIT: Perhaps https://en.wikipedia.org/wiki/Dimensional_analysis
| would give you the formula, and the constant you could get by
| experiment, and then the same formula might be applicable to any
| similarly shaped racquet.
| bloak wrote:
| 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).
| zhacker wrote:
| 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.
| BarryGuff wrote:
| Proves that there's literally an app to do anything. I'm amazed.
| Good job!
| zhacker wrote:
| thank you :)
| nwatson wrote:
| The 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
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