You Can Build A Little Car That Goes Farther Than You Push It

Can you build a car that travels farther than you push it? [Tom Stanton] shows us that you can, using a capacitor and some nifty design tricks.

[Tom]’s video shows us the construction of a small 3D printed trike with a curious drivetrain. There’s a simple generator on board, which charges a capacitor when the trike is pushed along the ground. When the trike is let go, however, this generator instead acts as a motor, using energy stored in the capacitor to drive the trike further.

When put to the test by [Tom], both a freewheeling car and the capacitor car are pushed up to a set speed. But the capacitor car goes farther. The trick is simple – the capacitor car can go further because it has more energy. But how?

It’s all because more work is being done to push the capacitor car up to speed. It stores energy in the capacitor while it’s being accelerated by the human pushing it. In contrast, after being pushed, the freewheeling car merely coasts to a stop as it loses kinetic energy. However, the capacitor car has similar kinetic energy plus the energy stored in its capacitor, which it can use to run its motor.

It’s a neat exploration of some basic physics, and useful learning if you’ve ever wondered about the prospects of perpetual motion machines.

25 thoughts on “You Can Build A Little Car That Goes Farther Than You Push It

  1. You don’t need a generator for this. It works just as well with a geared down flywheel. That’s how those push-along toys operate. Work is done spinning up the flywheel, and then when you let go the flywheel drives the wheels.

    1. This is mentioned in the video. You could also store the energy in some sort of spring, which is how the rubber-band driven guys work, too.

      The difference, as he notes, is that because those are mechanically connected to the wheels, you can’t just pick it up, stop the wheels, and just carry it around because the flywheel/spring will just drive the wheels entirely. Because the energy’s stored electrically and it’s got a dead zone (due to the reed switch) it’s kinda neat because you could just charge it up, stop it, hand it to someone and tell them to give it a push, and it’ll zip off by itself without them understanding where the energy came from.

        1. Yeah. It’s a cute trick. You hand it to someone, say there’s no battery at all in it, have them push it and it goes, etc. etc. Just a cute toy idea to get a kid thinking.

          1. Saying there’s no batter when it has a capacitor seems disingenuous.

            Yes, capacitors, super caps, and batteries are all different things, but when you say it doesn’t have batteries, most people interpret that to mean it’s not powered by electricity (assuming there’s no cord).

      1. I did, and yes, he gets to it at the end, but its like watching a 1hr special of a historical dig to find there was nothing at the end, so the entire video is set as some discovery of something, when it could have been said at the beginning in 30seconds, then we could have followed his journey. Atop this, HAD also give this misleading trap of tittle and bait to perpetuate it.
        And to all the flamers who say dont watch then or go away, sorry not fanboying anything, there needs to be criticism and counter arguments to achieve better. Otherwise imageing scientific peer reviews all wanking off each other instead of questioning, we would be teaching flat earth today.

        1. “Atop this, HAD also give this misleading trap of tittle and bait to perpetuate it.”

          Huh? What the heck are you talking about? Did you somehow think it’s magic that you can build a car that goes farther than you push it?

          So you never used one of those cars as a kid where you pull it back a bit to wind a spring or something and then let it go and it zips off?

          1. Yeah , Can you build a car that travels farther than you push it? I was what kind of question is that? I mean when the starter (or it was the battery?) of car is not working, you can still push it until the engine starts and then travel miles!

    1. F1 racing use this ”electric flywheel” technic to store the energy from the braking force into a curve to accelerate out of the curve.

      Yes it takes more force to push the capacitor car but if you need to brake anyway its better to use that force than heat up the brake discs.

        1. Hey, if you want to get pedantic, any vehicle with an alternator *period* recaptures energy when it’s slowing down so long as it’s not in neutral or clutched. All vehicles have been electric to some degree for like, 100 years: if you were clever you could *technically* improve gas mileage a bit by being smart about when you let the alternator charge the battery, but the benefits would probably be pretty low.

          If you look specifically at the idea of motor/generators, that idea’s actually from the late 1800s, and was used commercially in trains in the 30s. So yeah, really really old.

          1. Yes, it does.

            You’re actually wrong on two counts: first, for a huge number of vehicles still out there, there is no charge controller for the battery. It’s just a straight ~14.5V regulator and the battery takes whatever current it needs. Lead-acids are fine with a constant-voltage charge. Yes, newer cars are smarter about it, but they don’t need to.

            But second, and more importantly: the battery isn’t the only electrical load in the system. If you’re well above idle RPM (say going 2000-3000 RPM) and you take your foot off the pedal, the fuel injection system’s going to cut the fuel intake to zero.

            So where do you think all the energy to run the ECU, lights, infotainment, etc. comes from? It comes from the wheels, which are spinning the engine, which is spinning the alternator.

            Not exactly rocket science – this is why you don’t put cars into neutral to coast to a stop. Because it takes more fuel.

    1. And more efficiently as well. Friction in the gears and flywheel bearing are the only loss points with a flywheel … the motor/wheel/capacitor/gears/etc has several, not to mention a much larger air drag surface.

    2. It’s not the exact same thing as this uses a capacitor instead of a flywheel. That’s the whole point. He is not claiming it’s a brand new invention. Also those toys never stopped being cool, even for adults.

  2. Any car with less than infinite resistance will go farther than you push it. It’s not instantly going to stop once you are done pushing it. But that’s just semantics.

    You can also make a car go further than a passive car with just wheels. One way is to increase the push force and store the extra energy in a flywheel or capacitor like discussed in this video.

    But there is another way.
    You can do regenerative braking right after the push and then continue the rest of the trip at lower speed from the stored energy. At half speed you have a quarter of the air resistance. If your round trip loss is lower than the reduction in loss due to air resistance you can get further.

  3. It would be cool to do this on a bike. Skim off a little pedal energy – not enough to make you feel the drag – and effectively give yourself the momentum of a heavier bike when you coast.

  4. The comparison “same weight of the car” seems reasonable at first glance. But the extra weight is just used as cargo! I would have expected to have a flywheel version using the full extra weight budget for the flywheel mechanism.

    But I guess the generator/ motor would not stand a chance any more. And the results would be less click-worthy.

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