tesla, dc motors, torque, hub vs mid-drive

[ferrellms]

How many gears in a Tesla? (1) Are they slow off the line? Do they need more gears to climb hills?

Lots of posts here assume that Ebike motors need to "spin up" or that hub drives are slow off the line or that one drive train is "more efficient" than another due to torque multiplication that can take advantage of faster motor speeds.

DC motor have their highest torque at 0 rpm. Torque of a DC motor is mostly proportional to physical size. It is not the case that torque multiplication is important for ebikes unless the motor is too small (for example, a typical mid drive or geared hub drive) to provide enough torque to get up a hill. Big direct drive hubs have more torque to begin with and don't need any multiplication. And since the torque is there at the lowest speeds in any DC motor, a wheel speed rpm is fine.

Direct drive hubs have advantages - smoother, quieter, easier shifting, more efficient due to no mechanical losses, possibly more reliable due to fewer moving parts, less wear and tear on the drive train, and the ability to regenerate the battery (slightly) while riding. Mid drives have advantages - cheaper (do not underestimate the importance of this to manufacturers making design choices for their products), lighter, better front to back balance for going over big bumps (mountain bikes need mid drive) and no drag (albeit slight) from the motor when not pedalling.

And don't forget that a lot of the "feel" of an ebike is due to the controller systems that feed the motor juice and how they respond to pedalling, etc.

Teslas do have gear reduction in front of the one speed drive. But that is because a direct drive would require a physically huge motor to push a car without gear reduction, not because it would not work. E bikes can use direct drive with a reasonably sized hub motor.

Remember the 1 speed Tesla and just how fast it is before you buy the intuitively appealing but false argument that "torque multiplication" is important on a properly designed ebike and, in particular, that mid drives have an advantage over bigger hub drives in this regard.

 

[rich c]

Have you ridden a Bosch or Brose mid drive? I think you are presenting opinions based on Bafang mid drives since I've never ridden anything quieter or smoother than a Brose mid drive.

 

[Ravi Kempaiah]

@ferrellms ,

Seems like, you're a geek just like me. I can understand many of the sentiments here. It is frustrating when common mass buys into the idea that mid-drives are better in all aspects.
Most dealers are not engineers and they have no clue as to what the system. They just buy into the marketing gibberish. This thing gets perpetuated endlessly.

My friend runs a huge YouTube channel called "Learn Engineering" with 1.1 million subscribers. He does an extraordinary job in explaining things clearly. This particular video may be of interest to this thread.

 

[ferrellms]

@ferrellms ,

Seems like, you're a geek just like me. I can understand many of the sentiments here. It is frustrating when common mass buys into the idea that mid-drives are better in all aspects.
Most dealers are not engineers and they have no clue as to what the system. They just buy into the marketing gibberish. This thing gets perpetuated endlessly.

My friend runs a huge YouTube channel called "Learn Engineering" with 1.1 million subscribers. He does an extraordinary job in explaining things clearly. This particular video may of interest to this thread.

OK, good video.

 

[Trail Cruiser]

How many gears in a Tesla? (1) Are they slow off the line? Do they need more gears to climb hills?

Lots of posts here assume that Ebike motors need to "spin up" or that hub drives are slow off the line or that one drive train is "more efficient" than another due to torque multiplication that can take advantage of faster motor speeds.

DC motor have their highest torque at 0 rpm. Torque of a DC motor is mostly proportional to physical size. It is not the case that torque multiplication is important for ebikes unless the motor is too small (for example, a typical mid drive or geared hub drive) to provide enough torque to get up a hill. Big direct drive hubs have more torque to begin with and don't need any multiplication. And since the torque is there at the lowest speeds in any DC motor, a wheel speed rpm is fine.

Direct drive hubs have advantages - smoother, quieter, easier shifting, more efficient due to no mechanical losses, possibly more reliable due to fewer moving parts, less wear and tear on the drive train, and the ability to regenerate the battery (slightly) while riding. Mid drives have advantages - cheaper (do not underestimate the importance of this to manufacturers making design choices for their products), lighter, better front to back balance for going over big bumps (mountain bikes need mid drive) and no drag (albeit slight) from the motor when not pedalling.

And don't forget that a lot of the "feel" of an ebike is due to the controller systems that feed the motor juice and how they respond to pedalling, etc.

Teslas do have gear reduction in front of the one speed drive. But that is because a direct drive would require a physically huge motor to push a car without gear reduction, not because it would not work. E bikes can use direct drive with a reasonably sized hub motor.

Remember the 1 speed Tesla and just how fast it is before you buy the intuitively appealing but false argument that "torque multiplication" is important on a properly designed ebike and, in particular, that mid drives have an advantage over bigger hub drives in this regard.

How many gears in a Tesla? (1) Are they slow off the line? Do they need more gears to climb hills?

Tesla is not an ebike. The electric car trend goes toward single speed. The ebike trend goes toward light weight mid drive with multiple speeds. Two different things.

Lots of posts here assume that Ebike motors need to "spin up" or that hub drives are slow off the line or that one drive train is "more efficient" than another due to torque multiplication that can take advantage of faster motor speeds.

True, Bosch extensively did their research and development of their ebike motors, they actually engineered it so the efficiency window also falls within the efficient operating range of a human cyclist.
There is an efficiency window for an ebike motor.

DC motor have their highest torque at 0 rpm. Torque of a DC motor is mostly proportional to physical size. It is not the case that torque multiplication is important for ebikes unless the motor is too small (for example, a typical mid drive or geared hub drive) to provide enough torque to get up a hill. Big direct drive hubs have more torque to begin with and don't need any multiplication. And since the torque is there at the lowest speeds in any DC motor, a wheel speed rpm is fine.

That would be valid up to a limit. Try riding your hub drive and making stops along the way on a 30% grade hill. Your battery will drain much faster and your motor will quickly over heat. Sure it could go faster if given room to launch but the efficiency still goes down badly.

Tesla has been using AC motors not DC motors (for your information). Please be informed before you start your analogies and arguments. https://teslamotorsclub.com/tmc/threads/why-does-tesla-use-an-ac-motor.25917/page-2

Direct drive hubs have advantages - smoother, quieter, easier shifting, more efficient due to no mechanical losses, possibly more reliable due to fewer moving parts, less wear and tear on the drive train, and the ability to regenerate the battery (slightly) while riding. Mid drives have advantages - cheaper (do not underestimate the importance of this to manufacturers making design choices for their products), lighter, better front to back balance for going over big bumps (mountain bikes need mid drive) and no drag (albeit slight) from the motor when not pedalling.

Let's not forget that motor size and copper mass also has an inherent parasitic efficiency lose. The smaller the motor, the less parasitic lose.

Teslas do have gear reduction in front of the one speed drive. But that is because a direct drive would require a physically huge motor to push a car without gear reduction, not because it would not work. E bikes can use direct drive with a reasonably sized hub motor.

Actually, the automotive engineering vehicle propulsion guide for electric cars recommended a 2 speed transmission as adequate for the car's requirement, in contrast to a multiple speed transmission for the internal combustion engine cars. However, in actual practice the transmission did not hold up, so the solution was to use a more robust single speed with the gear ratio closer to the second gear for acceptable highway cruising but the motor has to be beefed up (HEAVIER) so it can endure a high power input (with assoc inc torque and heat) when moving from a stop or when climbing.
https://www.autoblog.com/2008/01/23/breaking-tesla-has-a-solution-for-their-transmission-woes-get/

Remember the 1 speed Tesla and just how fast it is before you buy the intuitively appealing but false argument that "torque multiplication" is important on a properly designed ebike and, in particular, that mid drives have an advantage over bigger hub drives in this regard

Once again. Tesla is not an ebike. The electric car trend goes toward more ROBUST single speed. The ebike trend goes toward LIGHT WEIGHT and EFFICIENT mid drive with multiple speeds. Two different things. You are making your own false argument.

 

[Ravi Kempaiah]

How many gears in a Tesla? (1) Are they slow off the line? Do they need more gears to climb hills?

Tesla is not an ebike. The electric car trend goes toward single speed. The ebike trend goes toward light weight mid drive with multiple speeds. Two different things.

Lots of posts here assume that Ebike motors need to "spin up" or that hub drives are slow off the line or that one drive train is "more efficient" than another due to torque multiplication that can take advantage of faster motor speeds.

Once again. Tesla is not an ebike. The electric car trend goes toward more ROBUST single speed. The ebike trend goes toward LIGHT WEIGHT and EFFICIENT mid drive with multiple speeds. Two different things. You are making your own false argument.

Mark,

No worries. This is not a competition. We are all learning here.
I too had many misunderstanding but over time, experience and outside knowledge has been invaluable.

There is no one solution for all. While I thoroughly enjoy the hub drives, I do think they are a must for off-road. This is an evolving technological space but certain truths of physics don't change over time. You provide some excellent reference material here for people to read and enjoy.

Take it easy.