3244: Pullback Drive

2026-05-13T06:53:05Z

92.208.67.235: /* Explanation */ Reference to Bacigalupi's novel "The WIndup Girl" added.

{{comic
| number = 3244
| date = May 11, 2026
| title = Pullback Drive
| image = pullback_drive_2x.png
| imagesize = 303x292px
| noexpand = true
| titletext = "How does the spring not run out almost immediately?" "We pull it back REALLY far."
}}

==Explanation==
{{incomplete|This page was created by A STOMP ROCKET POWERED CAR. Don't remove this notice too soon.}}

This comic is a reference to toy cars with {{w|pullback motor}}s. Normally used for small toy cars, a spring motor stores potential energy when the car is pulled backwards, and the potential energy (including the final energy used in holding the car against its spring) is suddenly released as kinetic energy when the car is released.

The very simple version of pull-back car will only go as far forward as it is drawn backwards in the first place. More complicated versions can use a change in effective gearing (through the use of a 'flappy' gear that meshes differently depending upon the relative direction of movement of the cogs it is meshed with) between 'charging' the spring by back-pulling, and then letting it 'expend' in the forward direction. This can allow it to store a lot of torque from a little pre-pulled distance and then expend it to give far more effective speed/distance to the very light toy. Through a free-wheel gearing at the end of its 'powered' phase, the car may run on 'unpowered' for a significant further distance. However, since there is a finite amount of energy that can be stored in the spring, they may hit a hard limit where the spring cannot be wound any further, or commonly a slip-gear will simply click as the mechanism no longer tries to convert pull-back movement into sprung potential (letting the child know that their toy is at maximum readiness).

In this comic, [[Hairy]] suggests a full-scale version of a pullback car, including the mechanism that clicks as it hits the limit of its spring-winding. Making this type of energy store work on the scale of a full-size car would be extremely impractical, due to the {{w|Energy density#In material deformation|low power}} and the requirement to pull it back far enough to then go anywhere meaningful, even assuming a multiplying effect on forward travel compared to the initial backwards travel. Hairy tries to sell the car by saying that [[Cueball]] won't need to worry about gas or electricity prices. This is [[technically]] true, but cars that run on petroleum or electricity have the advantage of their energy supply being refillable, while this pullback car seemingly does not (without another factory-style 'pull back' facility).

A car which is powered by such a simple spring mechanism would have the significant disadvantage of not being able to have a "Reverse" gear setting.

The worries about electricity and gas prices may be a reference to the closure of the {{w|Strait of Hormuz}} due to the {{w|2026 Iran war}}. The strait was a very common waterway used for the international trade of natural gas and petroleum from the Middle East, but the Iranian government is currently not allowing any foreign ships to pass through it. If this type of propulsion works, this would negate the need to fuel the car, making it a good energy-efficient alternative if it could be practically implemented. But hopefully they don’t give the car too {{What If|61|much energy.}}

It would be possible to "recharge" such a car by repeating the process of pulling it backwards, or perhaps by placing it on a treadmill-style arrangement and running this forward relative to the car, while holding the vehicle stationary. However, the energy being stored in the spring motor would have to come from somewhere. No clue is even given to what form of mechanical device is used to pull the car back at the factory and if/when it needs to be retensioned again, but the means used to power ''that'' might entirely defeat the main purpose of the pullback car (that that it doesn't rely on various fuels to keep it going) if it relies on such fuels itself.

A flywheel connected to the motor could occasionally be lowered onto the road when the car is under braking and then automatically raised, which might work as a form of charging if the released kinetic energy could be diverted to the main wheels. However, the automatic lowering and raising of the flywheel would require an external energy source, and it would be much simpler to just use an electric car at that point. Plus, this would produce diminishing returns and the car would need to be "recharged" every so often.

Also the power relies on the car 'being pulled back', which would present challenges and, as Cueball points out in the title text, such a motor would store very little energy and (in a vehicle the size of an actual car) would run out almost immediately compared to a traditional combustion or electric engine. Hairy responds that they "pull it back '''''REALLY''''' far", which would not actually solve the practical problems of it being an incredibly inefficient energy source, or the various other difficulties, particularly as it is bound by the inbuilt 'clicking-limit' that already is implied to have been reached.

To some extent, the spring-powered car is a direct analogue to electric cars (whether pre-charged at the factory or not), where forms of externally-generated power are transfered to a 'potential' held within the vehicle to be re-expended (with acceptable losses in conversion efficiencies) as movement. By contrast, fuel-powered cars provide the energy in the form of potential-holding material (LPG, fuel-oils, or even solid fuel like coal or wood, depending upon the vehicle), which is expelled after use and refilled with new supplies. The advantages of electrical power are that it can be relatively easily generated by means ''other'' than burning fossil fuels, and (while not currently at energy densities comparable to common engine fuels), the weight of batteries required to power a car over a given distance isn't anything like as problematic as the equivalent spring-based system would be.

Fun Fact: Paolo Bacigalupi's 2009 dystopic SF novel "The Windup Girl" is set in a post-petroleum world where this kind of propulsion is normal. Spring technology is incredibly advanced compared to our present. Cars are powered by springs that are wound-up in factories on treadmills with genetically engineered mastodons. These springs can then be placed into cars and other machines. They are exchangeable, so if one spring runs out, you replace it with another. Fuel-powered cars still exist, but are only used by the military, and the motor sounds they produce have a terrifying effect on the general population, because they are not used to those sounds anymore.

==Transcript==

:[Hairy and Cueball are standing to the right of a medium-size car. Hairy has raised one hand slightly to point to the car.]
:Hairy: You won't have to worry about gas prices '''''or''''' electricity prices with our new pullback drive model.
:Hairy: At the factory, we put the car on the ground and tow it all the way backward until it starts clicking.
:Hairy: To drive forward, you just release the brake and it goes.

{{comic discussion}}<noinclude>

[[Category:Comics featuring Hairy]]
[[Category:Comics featuring Cueball]]
[[Category:Physics]]

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3244: Pullback Drive