Why we don't use gears

This might be a really dumb question but I'm trying to understand why we only have a motor and no gears. Besides lacking simplicity, wouldn't gears allow for better power usage (and we could in theory use a shitty motor too)? Just trying to understand

-Akshay Gaitonde

Gas / diesel engines have a non-linear torque curve that makes transmissions necessary, electric motors have a Linear torque curve

Gearing isn’t all that efficient, we use it in gas motors to make up for a lack of RPM or lack of torque, something that electric motors don’t suffer from

-Sidharth Babu

Fundamentally, the issue is that gas motors are driven by a bunch of small impulses from burning gas in each cylinder, so having the main drive shaft In a cylinder go too slow will result in a very jerky torque profile (unless you have a shit ton of cylinders), and since friction is difficult to characterize at low speeds + it's really hard to dynamically vary the amount of gas you aerosolize into a cylinder and do the sensing of temp and gas composition you need to make an accurate guess as to the torque that main crankshaft would get, so it's hard to just reduce the amount of propellant

In sum, IC engines stop working well at very low speeds (jerky movement) and at low torque (hard to cycle reliably)

In practice, the low torque thing is actually semi solvable but the low rpm isn't (it's a function of how many cylinders you have and more cylinders =complexity/time/money) so you typically have gas engines shoot for a high enough rpm so that the torque impulses blend together into a semi continuous profile (same concept as half rectifier plus a cap), then using gearing to reduce the speed where nessecary

TL;DR: an IC engine is like a power supply that has a voltage that varies wildly if you don't pull a certain amount of current from it, so in typical use, you would pull high current low voltage to keep your power output relatively steady and use a boost converter to get it to a usable range (in this context, a gearing system is a boost converter)

Adding gear trains is also an energy sink which is pretty bad since solar racing is defined by low power availability, the general rule is that each gear interface in a gear train reduces the output power by ~10%. This application would also qualify as a high speed gearbox, and those are super difficult to design (See preload and fatigue/wear calcs)

-Jacob Yan