I don’t quite understand the use of a gearbox. What is the purpose of it?
Say for example some machine use a gearbox for some reason is it possible to replace it with a motor and a speed contorller?
Thank You.
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It is very common to use electrical motors with gearboxes too. The gearing will typically be fixed but it is still a gearbox.
The reason is the torque and power you can get out of an electric motor with a specific RPM depend on the size of the motor. The torque of an electric motor will remain close to constant up to a specific RPM but the power increase linearly to that point https://images.theconversation.com/files/269180/original/file-20190414-76843-99pwbb.png
If you have 3:1 gearing and a smaller motor at 3000 RPM you can get the same torque and power as a larger motor at 1000 RPM. A small motor and gearing can be lighter and cheaper than a larger motor with no gearing for a specific torque, power, and RPM requirement.
Cost and weight are why electric motors typically have gearing. Advanced speed control can be used with gearing to provide enough power and torque at the RPM you what too. It is not an either-or situation.
An electric motor has a larger usable RPM range and especially at close to 0 RPM compared to an internal combustion engine. The curve of them looks like https://images.theconversation.com/files/269179/original/file-20190414-76843-15kch50.png A typical ICE (internal combustion engine) car engine will operate at 2000-300 RPM most of the time and requires a changeable gear to handle the speed range you like to drive.
Electric cars have gearing and motors that have their speed controlled to provide max torque. If you use as large part as possible of the electric motor RPM range you can use a smaller motor and gearing to get out the same amount of power and torque. There is a limited speed range cars operate the wheel RPM will never be as high as the max operation RPM of an electric motor. a typical car has a wheel circumfluent of around 2.3 meters. At 6000 RPM the speed would be 828 km/h. The speed record for engine driven- land vehicles are 648km/h. Electric motors can often operate at 15000 RPM, aht is a speed of 2000km/h or mach 1.7. Regular cart tires would rip themself apart at speed like that. Cars have mange supersonic speed with jet engines, they used solid metal wheels.
The speed control part will cost money too so if you can have the electric Synchronous Induction Motor operate directly attached to the power grid the RPM you get depends on it winding and the power grid frequently. Here is a table od the synchronous speed https://slidetodoc.com/presentation_image_h/13597912199d12a740032f62bccdc080/image-25.jpg So you can build a cheaper system by having a Synchronous Induction Motor with a fixed RPM and then use gearing to get the RPM you need.
Selecting between an ICE and an electric motor is not about the need for gearing or not. It is about the availability of electrical power, the inconvenience of having a coord to a device, the cost of batters, problems with ICE exhaust, noise, limitations in battery recharging etc.
An ICE will be lighter, and cheaper than batteries and an eclectic motor if the power requirement and usage time is large enough. A lawn mover is a good example, you use electricity for noise and pollution reason not because the are cheaper.
When you get to cars the cost of of fuel vs elecicity can result in a electic car being cheaper ofve its total life, the initial cost will be higher. Then there is the enviomrnetal factors.
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