How Fast Can We Spin A Titanium Skateboard Wheel?

How fast can we spin a titanium skateboard wheel? There's only one way to find out. I made a custom wheel in pursuit of our goal of reaching 200,000 RPM. We used our 60,000PSI waterjet to spin it up to outrageous speeds.

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[WaterjetChannel]

What would you guys suggest on how to get our RPMs higher? Our next three strategies are to try lighter materials (magnesium or carbon fiber), hollowed out wheels, and finally smaller diameter wheels. At this point those seem to be our only bottle necks, anything we’re over looking?

[yourbifriendaspen]

If you're asking if it would produce a sonic boom, that's a no. A spinning object doesn't produce the kind of compression force needed for a boom. A sonic boom is produced when air is compressed at a faster rate than it can expand itself. The wheel would have to be moving, not spinning.
Since the wheel is a uniform shape, there's nowhere along the wheel for air to accumulate and compress.

As far as producing a different pitch or tone, though... That's beyond me. I'm not familiar with that part of physics

[JustHarrison]

Should have just drawn a white line on the wheel

[jacksonjohnson]

Jet engine engineer here.

First, fun to see the resin wheel break into thirds, that's exactly how a disk would be expected to "burst" as it's called at my company. You can see the damage that little thing did to your machine. Imagine what would happen if a 200lb chunk of nickel broke up like that.

Second, do NOT hollow out the inside. Material closest to the rotation axis is actually what is doing all the work to hold the disk together. It's also the most efficient material in terms of added strength/weight.

Third, while I don't know the dimensions of your wheel, the outer diameter might already be breaking the sound barrier. A 60mm wheel would have to spin to 109k RPM for the outer edge to reach the sound barrier. As others have stated, due to the smooth outer surface, there really isn't anything to generate a shockwave and make an audible sound. This is outside my lane, but I question your speed estimation methodology. How do you know the frequency you are picking up is the once-per-rev tone and not something like the passing frequency of the bearing balls

[AuburnTigers]

This is the type of unhinged video that got me hooked on youtube back in its early days.

[MushookieMan]

I'm an engineer. The limiting factor on wheel RPM is parasitic drag from air resistance and bearing friction; not the weight of the material. If you had low enough friction, the outer surface would achieve the same velocity as the jet. The best way to achieve lower air drag is to polish the surface of the wheel, and place the whole contraption in a somewhat airtight cylindrical container, so a rotating mass of air can form around it, instead of accelerating the stationary air in the room. But by far the biggest improvement could be had by removing the grease from the bearing. After all you only need it to work once.

[the.other.ian.]

Since the titanium isn't gonna get gouged out as much, to maximize the speed you are gonna want to have it hit the wheel further out so the water stream is hitting at an angle closer to tangent of the surface of the wheel.

[SMG-PERFORMANCE]

It accounts as ALL OF IT. -certified googler here.

[Scyth]

0:10 I laughed way too hard and I have no idea why lmao

[keithmiller]

I know! I'll just leave it on the ground!"

Sent me to space, MY SIDES

[joanrucker]

The little sayings complete with original video clips are killing me😂❤

[matthewlambermon-southam]

my guess would be the tachometer functions on contrast to generate a differential pulse wave, then just spits out pulses per second to pulses per minute to get RPM, the blue anodization may have hindered the contrast (red laser), so maybe try a white spray paint and the sharpie black line, a wider black line may be beneficial because at higher RPM the contrast would produce a fainter pulse signal for a thin one with respect to the sensors sample rate.

[Gunbudder]

you calculate the upper limit on rotational velocity for the titanium wheel. the wheel will never spin faster than the surface velocity of the water hitting it. so you use the formula to convert surface velocity of a wheel to rotational (using the radius of your wheel) and that is your absolute upper limit. you know it will actually be less than that because the frictional forces of the bearing and the air will slow it down. you can combine all frictional forces into an overall coefficient of friction. you can get the drag coefficient for a stationary spinning wheel from an engineering data table, and you can get the coefficient of friction for that bearing from the supplier (or just do ceramic on ceramic). my WAG would be the actual rotational velocity maximum after friction is probably 80% of the frictionless value.

The slowmo doesn't actually tell you the whole picture though either. it appears to be spinning 3 frames for full rotation, but you could be spinning a lot more than that. the sample rate of the camera could be relative slow such that the wheel spins multiple times per frame and simply shows up in a different location. there are a LOT of formulas for calculating and accounting for this to try and get a range of possible values.

also the frequency is going to be tied to the density and volume of the disc, so it wouldn't map perfectly to the aluminum disc

[fearlabsaudio]

I got about 56300rpm using a spectrum analyzer on the audio. 1 rotation = 1 period/rotation. It made a fundamental tone at roughly 938hz * 60.

[esolo]

Strongbad reference =subscribed. Way back in the archives of the interwebs.

[kswis]

One of the most underrated shows on the tube

[brandonb]

No bearings find a way to suspend a much smaller wheel with magnetism.

[biomechannibal]

Thank you for the Strong Bad reference.

[MrAPCProductions]

The Cheat is to the Limit, cmon fhqwhgads .

[Ofna]

Great entertainment. I can tell you have working around this shop forever as your ability to cover all ideas or theorys with tests along with funny spats makes this very fun to watch! Great job!