What would be the easiest way to get the rpms of a bicycle tire?

[GreenAce92]

This might be easier since it is stationary.

I was thinking about a clamp-on IR beam-blocker which I would place a black sticker on the rim, and assuming the shiny part of the rim reflects, then I should get a difference between non-sticker, and sticker part of the rim.

I would then use the measured radius from the hub to the sticker to calculate rpms right?

Do you think that the IR reader can get a good enough threshold/range/difference between bounce/no-bounce?

So with the shiny part it's bouncing same rate, then hits the black part, should absorb some of the waves... this sounds like a bad design

Maybe a spoke-clip on thing that reflects the signal back to the emitter.

 

[c_mitra]

Yes, your idea is good but consider using a modulated beam so that interference from ambient light is reduced. Perhaps you can use one of the detectors used for the remote control in TVs (and other related gadgets). They use a rather simple design and can be quite sensitive.

 

[BradtheRad]

I once drew uniform black lines on a steel flywheel inside a cassette deck. I wanted to measure its speed. The black marker made lines 1/8 or 1/4 inch wide. I lit them up with a bulb. These were able to be detected by a phototransistor placed close to the flywheel.

Your idea seems okay, in view of it being in the same league with my method.

 

[GreenAce92]

Thanks for the input guys.

It would ideally be easily reproduced by other people who are less-tech inclined but right now just getting the basics.

I'm just envisioning a clip, clothes-line style and a bendable arm like those desk lamps, clip it onto the frame, then aim it at the rim.

I think maybe an A design would be in mind, where a photoresistor is on one end and the IR led is on the other, unless side by side is the best.

The A would have problems with adjusting proper depth to reflect at the right angle.

 

[c_mitra]

I guess side by side is the best and use a piece of sticker tape that uses the corner reflectors.

 

[GreenAce92]

Corner reflectors? Is that just regular reflective tape?

 

[c_mitra]

Right. They use small cubic reflecting particles that always reflects the light back by 180, whatsoever its orientation may be. Regular reflective tapes have them in plenty...

 

[BradtheRad]

Also consider detecting the tire valve. It's a larger diameter than spokes, therefore its silhouette is wider. You would need to find a way to distinguish it from spokes. Your detector needs to be mounted on the opposite side of the tire from the led.

 

[KlausST]

Hi,

The light/reflection method is sensitive to dirt.
That's why they use the clip on magnets.

Calculation:
For RPM you don't need to know the radius.
But for speed you need to know the radius.

Klaus

 

[hobbyckts]

Check this link...It may be useful..

https://endless-sphere.com/forums/viewtopic.php?f=28&t=16114

 

[GreenAce92]

Hi,

The light/reflection method is sensitive to dirt.
That's why they use the clip on magnets.

Calculation:
For RPM you don't need to know the radius.
But for speed you need to know the radius.

Klaus

I can see the magnetic version (magnetometer?)

I'm curious why rpm doesn't need radius?

Well... although the tip velocity will vary by diameter, the whole spoke is still rotating at the same RPM?

What would matter then, the size of the surface area? I mean how would you even calibrate it in the first place?

Unless it's just counting break, working, break... which I would think is influenced by the size of the breaker (width).

Interesting catch

Also although I might not have specified, this is for indoor application, riding a bicycle while wearing a VR headset, the rpms/turning inputs are fed into the app to modify the experience, speed, playback, etc...

That's the thought anyway

- - - Updated - - -

Also consider detecting the tire valve. It's a larger diameter than spokes, therefore its silhouette is wider. You would need to find a way to distinguish it from spokes. Your detector needs to be mounted on the opposite side of the tire from the led.

yeah could have a U - design where the U goes over the tire provided a sufficient distance maybe a screw that you twist like a vice to vary the distance between the transmitter/receiver and the reflector panel.

C_mitra, thanks for the tip regarding the reflective tape.

Thanks for the link hobbyckts.

 

[c_mitra]

About the sensitivity: you can experiment with a simple reflective tape (white metallic color) fixed on a black cardboard and your remote control for the TV. The remote uses an IR LED and you cannot see the beam but the result can be seen. You can also put a bit of mud on the reflecting tape and see the effect for yourself. Remember that the reflecting tape always reflects the beam by 180 deg whatsoever the orientation of the tape may be and you need to stand on the same side of the TV (or whatsoever receiver is being tested).

 

[GreenAce92]

Believe it or not, I don't have a TV.

Many monitors and computers.

About the mud, this is intended for indoor stationary bike but this is a good thing to keep in mind.

I had an idea (not directly related) but to treat the tire as a brushless motor.

Put a bunch of magnets on the rim, then have two eletromagnets on ejrhed side, to push the tire.

If would seem to me that applying the force with the largest moment arm (rim), does not require a lot of power. But that's two poles. Maybe bump it up to four, but that's an even number not divisible by three(not three phase)

I figured could skip transmission by direct drive like a brushless outrunner motor.

I'm not even sure if the stator/magnets would even be oriented right.

 

[KlausST]

Hi,

I'm curious why rpm doesn't need radius?

RPM = revolutions per minute.

RPM = 60 x pps (pulses per second)

if you see one pulse per second, then it is 60 RPM, independent of wheel size.

***

If you use 28-406 wheel the the circumference is about 1451mm

speed is: circumference x pps = 1451 mm x 1 pps = 1451 mm/s = 1.45m/s = 5.22 km/h ( with 1 pps)

Klaus

 

[GreenAce92]

Hi,


RPM = revolutions per minute.

RPM = 60 x pps (pulses per second)

if you see one pulse per second, then it is 60 RPM, independent of wheel size.

***

If you use 28-406 wheel the the circumference is about 1451mm

speed is: circumference x pps = 1451 mm x 1 pps = 1451 mm/s = 1.45m/s = 5.22 km/h ( with 1 pps)

Klaus

Thanks for that explanation.

Revolution gets me, aye need to read up ha.