Is it possible to build a hamster chariot?
September 9, 2013 2:55 PM   Subscribe

A single hamster inside a sphere can propel itself around a room. Likewise, one could imagine that two hamsters in tiny harnesses would be able to pull something small… perhaps another hamster on a tiny skateboard. My question is whether it would be possible to translate the locomotive energy of hamsters (perhaps using pulleys and hamster wheels) enough that it could pull a light vehicle seating a ~50 kg person (the chariot), or whether the friction and the necessary weight of the apparatus itself would place an upper-limit on the amount of energy one could extract from hamsters.

I realize it's a silly question, but it's something I have pondered for a very long time.
posted by Frankieist to Travel & Transportation (15 answers total) 13 users marked this as a favorite
This seems like a great question for Randall Munroe.
posted by shesbookish at 3:01 PM on September 9, 2013 [2 favorites]

I think you need to specify a minimum speed. Given steep enough gearing I think you could do this with a single hamster, the movement of the vehicle would just be imperceptibly slow (i.e. the hamster wheel might have to go around thousands of times for one rotation of the chariot wheels.)
posted by contraption at 3:02 PM on September 9, 2013 [1 favorite]

That's a good point. Assume a perfectly flat surface and a terminal velocity of at least 3 km/h (or, if it's less than that, what would the top terminal velocity be?).
posted by Frankieist at 3:05 PM on September 9, 2013

In theory, yes, it should be scalable. One hamster can run enough to turn a wheel, plus a certain amount of extra friction. The limit is when one hamsterweight clinging to the front wall of the wheel is insufficient force to turn the wheel. So, for a 120g hamster, that's ~1 Newton of force. Or take 120g, gravity, and the size of the wheel, calculate its moment of inertia, and get an angular acceleration. Then just multiply by the number of hamsters and wheels until you get enough angular acceleration to convert into forward force (by your mechanism of choice) that you overcome static friction.

One obvious upper limit on speed would be the speed that hamsters like to run at, which the internet cites as being ~1.8 miles per hour.

But how do you convince that many hamsters that they all want to start running on the wheels at the same time?
posted by aimedwander at 3:20 PM on September 9, 2013

You'll probably want to rig up something with freewheels and reverse gears so that the hamsters would always be working together no matter which direction they run.
posted by ckape at 3:46 PM on September 9, 2013

Wouldn't the most straightforward approach be to rig up many many hamster wheels to generators?

They could then trickle charge a battery and you could drive your chariot around.
posted by Just this guy, y'know at 3:59 PM on September 9, 2013 [1 favorite]

How would you get them to all run in the same direction? If you find a way to solve this, a hamster would need to be attached to a very long string, of reasonable materiel, indeed to no longer be contributing productive force.
posted by Blasdelb at 4:06 PM on September 9, 2013

Hey there, I've just done a really quick calculation to see if this feasible:

By googling around I found this forum where someone has attached a generator to their hamster wheel. They measured a peak output of around 150mA at 3V.

So this gives us peak hamster power output (PHPO if you will) as P = IV = 0.15 A * 3 V ~ 0.5 W.

Then I went on Wolfram Alpha, and used this calculator for cycling. Wolfram says for 1 min at 3kph we will use 2 Cal of energy = 8.37 KJ. I have no idea how their calculator works or whether it's accurate for such a low speed, but hopefully it is.

As power is energy / time, we can work out the power the bike needs to move, P = 8370 J / 60 sec ~ 150 W.

By comparing this to our PHPO you can see that it would take approximately 300 hamsters running flat out to pull a 50kg person at 3kph. This is probably an underestimate as I'm assuming that your chariot/hamster set up will be as efficient as a bike/person one, which to be honest I doubt. However, I reckon if you increased the number of hamsters by a factor of ten you should be ok.

Also note that the forum said that the hamster would tire quickly at the 150mA output, but at 50mA he'd keep going for 3-4 hours. So if you want a marathon rather than a sprint just triple the number of hamsters.

So, now I've done the hard work, I'd like to see a photo of you on a bike being powered by three thousand hamsters please.
posted by Ned G at 4:06 PM on September 9, 2013 [28 favorites]

But how do you convince that many hamsters that they all want to start running on the wheels at the same time?

This is probably where the cat comes in...
posted by ouke at 6:35 AM on September 10, 2013

Thanks Ned G for the well-researched response. Your answer helps hint at how many hamsters might be needed, but it doesn't address the central engineering problem—namely, how to scale the motive power of many hamsters. Solutions with generators or batteries are cheating (my interest is not in a hamster car, but a hamster chariot).

If I can build this I'll absolutely post pics. Though it might just end up being a schematic. Does Adam Savage still read AskMe? :-)
posted by Frankieist at 9:04 AM on September 10, 2013

You need a power storage device because I don't think you can get the required number of hamsters to work in unison to create enough power to get that amount of weight moving. You say generators or batteries are cheating but there are plenty of other ways to store potential energy including mechanical means. Pumping water to a tank with enough head to power the chariot is the oldest method of storing potential energy. This is something easily within the realm of a few hamsters working diligently over time and you would be hard-pressed to call that cheating.

Any direct mechanical means would still require storage of potential energy otherwise the number of hamsters and wheeled dynamos will be near infinite. The more you need will add weight and require more. It will be a vicious cycle in more ways than one.
posted by JJ86 at 10:45 AM on September 10, 2013

With 3,000 hamsters in a confined space you're going to run into sanitation concerns too, as the urine/feces/partially cannibalized hamster corpses will quickly start to gum up the works.
posted by contraption at 5:38 PM on September 10, 2013

I'm picturing some sort of cow catcher arrangement in the form of a trough at the bottom of the hamster wheel that would scoop up all that detritus (poop, dead hamsters, hamsters too weakened or lazy to keep up) and periodically flip to one side and jettison it all onto the roadway. Then you'd just need to pour in a couple dozen fresh hamsters every once in a while and you could ride in style indefinitely.
posted by contraption at 5:45 PM on September 10, 2013

I'm picturing an extravagantly mustachioed guy stripped to the waist and shovelling hamsters in through a hatch.
posted by Just this guy, y'know at 7:56 AM on September 11, 2013 [1 favorite]

Well he's not pulling the truck, but the hamster is "steering" it.
posted by sardonyx at 8:22 PM on September 20, 2013

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