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Comment by keyle | Hacker News Reader

Very cool but the original board was never designed to go at such speeds. I suspect you'll ruin the wheels fairly quickly, not to mention you might lose control at high speed fairly fast. I'm not a skateboarder myself, but I've moded some bikes and adding speed is the easiest part, making it useful speed is way harder.

Also, I hope the engine can go in reverse or this guy has no breaking power; and as he gets comfortable riding it, sooner or later, a surprise will happen and he will have no choice but jump ship.

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Regular longboards go much faster than an electric one like those described here. I recently built an electric skateboard using one of the ESCs in this post and on flat ground it can't go much over 20mph. It goes far faster than that on even a slight slope. Maintaining control at that speed is dependent on the trucks.

The ESCs do have brakes. They make downhills easy to manage. The only problem is that, without some special components, the brakes don't function on a 100% full charge. (The brakes are regenerative, so the ESC watches the voltage and doesn't allow the motors to overcharge the batteries.) That's not a problem in 99% of cases -- it only matters if you start your trip on a large downhill.

That said, anyone learning to ride an electric skateboard should learn how to bail. You'll have to do it eventually.

A longboard downhill can easily go over that speed.

But then you get speed wobbles...

https://imgur.com/auUscXX

When longboarding downhill at high speed you need to put most of your weight on the nose of your board. This will prevent speed wobble completely (may depend on your board.) Source: bombing hills myself

Yeah I think if you are a downhill skater (I'm not) then maybe you it's not a problem, but seriously if you are not a good skater I really would not recommend going any faster than you can run on one of those things (or even a regular skateboard for that matter), pads or no pads. Source: skating parks for over 30 years (and still suck).

What you're talking about is yaw inertia, and as another comment points out it's solved by moving the weight to the front wheels.

See an explanation here: https://en.wikipedia.org/wiki/Automobile_handling#Yaw_and_pi...

And a 30 second visualistion here: https://www.youtube.com/watch?v=4jk9H5AB4lM

Would that I had that knowledge 30 years ago!

Easy, lots of things you can do to prevent that. On the hardware side, tighten your trucks a bit (not too much as it will damage the bushings over time), use harder bushings (cheap), use a lower-angle baseplate for the rear truck (a bit more investment).

As hug mentioned, shifting weight helps. Also as you begin to catch wobbles, you can relax your stance a little bit to counteract them - but that takes practice. Finally, you simply control your speed - usually by sliding, but I can imagine on an e-board slides will be very cumbersome.

Of course if you know all of this, you probably already have realized that e-boards are barely good for anything but cruising from point A to B, and there's infinitely more breadth and depth to this sport than just that.

Source: I'm a roll cat ;)

I hit that speed regularly on mild downhills. Bombing a hill you can hit 80km/h pretty easily. I think the record is around 140km. Certainly not bragging, as it's not that impressive among downhill longboarders. Just trying to give some perspective.

What are you using to measure your speed? Do longboarders have an equivalent of Strava?

Sure, you can easily wear a GPS watch while longboarding.

Yeah I wasn’t asking hypothetically. I wanted to know what they actually used to record their speed.

GPS Phone apps and device like this.

http://www.lifehacker.co.uk/2015/10/27/the-lancaster-gps-spe...

I use this Speedometer app: https://itunes.apple.com/us/app/speedometer-speed-box-app/id...

There are some exotic cars that use GPS to measure their speed to save weight by not using a typical speedometer.

Do you have a source for this? It doesn't seem to make any sense because the speed sensor is normally used as an input for the engine and brake control systems. Not to mention the fact that the sensor is already extremely light because it's just a rotary encoder. GPS is also wildly inaccurate for speed measurement at low speeds and near tall buildings. I can certainly see using it in addition to a normal speed sensor for better accuracy at speed but as a replacement for weight savings it seems very unwise.

Indeed, I'd actually expect exotics of all cars to have 4-wheel speed sensors for traction control, launch control, etc.

I'd expect to use this 4-wheel sensor data along with the multi-axis acceleration data to calibrate the GPS, not the other way around.

It was a custom car on Jay Leno's garage though I forget which one. Maybe a lotus.

The latest record (2017) is ~150kmh

Yep, high speed can definitely ruin a wheel(!):

https://twitter.com/machinepix/status/969654857895301120

That's a bit more than 50 km/h.

not fair as those water jets can cut through just about everything.

In this case the water jet isn't cutting anything, just spinning the wheel very, very fast.

>Also, I hope the engine can go in reverse or ..

Small nit, there are motors out there that offer resistance/braking without reversibility.

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