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Comment by jlhonora | Hacker News Reader

Hi there,

If you liked this article perhaps you'll be interested in a project I've been working on. My wife has a Hedgehog (yeah, like Sonic) and he's pretty shy. He also has a wheel and runs ALL night.

To feel that he interacts a little more I connected a wireless node with a magnetic switch so I could count how many laps he runs every night, and therefore the equivalent distance. Every morning he tweets how much he ran, just like RunKeeper :)

Check out his twitter account here: https://twitter.com/runhedgie

And, of course, the code is hosted on github: https://github.com/jlhonora/iot

I just finished this project yesterday, but I have many more ideas to add. I'd like to correlate running activity with temperature (hedgies are pretty sensitive to cold weather) and ambient light. I'd also like to make a public API so that anyone can analyze his activity patterns.

So, stay tuned and follow!

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... now I feel terrible at slacking off at my jogging. Little guy is like 4 inches tall and running 5.8km last night.

Well, there's a catch with all of this. The wheel has some inertia, so running in it should be easier than running the same distance on the floor. The ran distance is still the same , regardless of this fact.

And I'm trying to keep up with my jogging as well :)

A body also has inertia that makes it easier to keep running. The wheel may have more, but that also means that it takes more effort to bring it up to speed.

Also, one should take air resistance (of the running body or the spinning wheel) into account.

In physics it's generally safe to assume that all the different air resistances and drags and so on cancel out. You just draw a force diagram and everything always cancels, otherwise the hedgehog would have constant acceleration which we know isn't true.

Boundary drag on the wheel as it spins causes a loss of angular momentum, and so it slows over time unless force is applied (via adorable hedgehog legs) to keep it constant. Additionally, there are likely normal frictional forces at the meeting of the wheel and the supports, as I highly doubt they gave the pet a wheel with magnetic bearings in a vacuum.

And yes, the hedgehog must exert constant force in order to overcome this viscous friction.

On a related note, this viscous damping term scales as velocity, so the faster the wheel turns the harder the little thing has to work to keep it at a constant velocity.

In high school homework physics, it is.

This is easily a business. Easily.

Also, how about hooking up a dynamo and trickle charging devices?

Yeah, I think so too. At least a Kickstarter project. You could sell an integrated wheel with this tweeting device.

I'm already a startup founder at http://satelinx.com and http://beetrack.in , apart from teaching Computer Architecture. I do have experience making and selling hardware, what I don't have is free time :)

I'm preparing a more technical description about the system (I designed and built the hardware myself), I should post it on the feed over the weekend.

As for the dynamo, definitely! But I'd rather let the hedgehog run as smoothly as possible.

> As for the dynamo, definitely! But I'd rather let the hedgehog run as smoothly as possible.

It wouldn't take much of a dynamo to provide enough power to trickle-charge a tiny battery for a microcontroller that can connect to wifi.

Also, if you're setting up a kickstarter, don't underestimate the marketing power of powering electronics off of a hamster wheel.

You are now the only twitter account I'm following. That's awesome.

Could make videos, they could be automatic montages of different parts of his run.

Definitely. I'm saving for an infrared raspberry pi camera: http://www.raspberrypi.org/tag/pi-noir/

I like what you are doing. Where are you from and how can I help you get one of these(it's very cheap, I am happy to buy a cool gadget for someone who does cool stuff). If you'd like, then send me an email to my nick at gmail.

Nice! I never quite finished my identical project 3 years back: see https://github.com/anthonydanza/whatsuphedgehog

At first it seemed like it would be posted automatically. But you read and interpret the data for your little friend, right?

It is totally automatic. I'm still working out the tweeting time, so some variability should be expected.

The phrases are random, check the code for them here: https://github.com/jlhonora/iot/blob/master/rpi/twitter_mana... . The "mood" for the phrases depends on the ran distance.

The graph I posted was generated with matplotlip and I tweeted it manually. When I finish struggling with D3 I'll put an on-demand graph with the data.

over 14km a day for such a small creature? That's insane.

I thought just the same. At first I thought there was an error with the counting, but there's a debounce of 0.2s for every pulse https://github.com/jlhonora/iot/blob/master/arduino/IoT/pir..... The wheel is not perfectly symmetric, and I'm placing the magnet on the opposite side of the reed switch used to count each lap, so that there's no risk of getting the switch stuck generating lots of pulses.

The activity graph (shown on the twitter feed) is for that same night, which seems to be quite consistent over time. There are no peaks either, so I think it should be accurate. After all, he does run all night.

Apparently it's pretty natural for these small animals to run such long distances. My wife has a hamster and they are known to run at least 9km a night. We had to find it a different room to live in because it will be up ALL night running, and running, and running.

A) this is really cool and B) your Antu the Hedgehog has shamed me into running again.

The units used on Twitter seem a bit odd, what are mts? I'm guessing kms is KM? Would that make mts meters?

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