Motor configuration

[Sidepod]

It just dawned on me that the TQ motor (Haibike) seems to be rare in that it is truly concentric in its design. All of the other motors (that I’m aware of so far) have the motor shaft and pedal crank shafts misaligned and rely on drive belts. This seems to me to be the obvious way to approach the problem

Doubtless someone will correct me.

Just an observation.

 

[DtEW]

It just dawned on me that the TQ motor (Haibike) seems to be rare in that it is truly concentric in its design. All of the other motors (that I’m aware of so far) have the motor shaft and pedal crank shafts misaligned and rely on drive belts. This seems to me to be the obvious way to approach the problem

Doubtless someone will correct me.

Just an observation.

And this is based something other than mere aesthetics of an exploded diagram?

If your rear wheel can be in the next county, sure. If short chainstays and/or large-tire clearance are priorities, or wanted as options, then no.

Also, you will need large-ID bearings for all the concentric parts (like the motor) to allow the crank axle to pass through. That has ramifications on weight, sealing, drag, etc.

Also, you will need to support all the bearings in a casing design out of parts that can be easily cast, and convey strength in the assembled structure.

I mean, how many car transmissions (another reduction gearset) do you know that are concentric?

 

[Mteam]

chainstay length and suspension pivot positions would be affected by a concentric type design, whether they are good or bad effects depending on the intent of the design

 

[Sidepod]

All good valid points.

Chainstay/swing arm pivot points all seem to be roughly around the periphery of the chain ring regardless of the type of motor so that may/may not be a consideration/limitation for the geometry department. The TQ casing is the same dia as the chain ring.

I'm not sure a vehicle transmission is the correct comparison, there are an awful lot more considerations when packaging an engine/gearbox unit in a car. Perhaps a MGU from a race car? Concentric "pancake" motor unit and inline with crank/gearbox input.
It would be interesting to measure actual torque levels at the pedal crank shaft as opposed to motor output shaft to get a true comparison of the losses between the two designs. Manufacturers do love to quote power/torque levels at the "brochure" as opposed to the wheels.
Interestingly I understand the TQ motor is rated at 300Nm but de-rated to 120 for e-bike use. Plenty of redundancy there.

Larger bearings means larger surface area so reduced load. Obviously a weight penalty but then offset by any belt drive hardware?

For me a big advantage of the concentric design is the down/battery tube remains intact. The battery can slide out downwards past the motor.
Cutting a large hole in the frame to allow battery access can only reduce torsional rigidity, a weight penalty being added to gain that stiffness back with increased lay up thickness perhaps?

 

[DtEW]

For me a big advantage of the concentric design is the down/battery tube remains intact. The battery can slide out downwards past the motor.
Cutting a large hole in the frame to allow battery access can only reduce torsional rigidity, a weight penalty being added to gain that stiffness back with increased lay up thickness perhaps?

Please see the Specialized Turbo Levo. You don’t need a concentric motor to make possible a fully tubular downtube w/a removable battery. You just need a motor manufacturer willing to tailor a casing for your design.

 

[Mteam]

For me a big advantage of the concentric design is the down/battery tube remains intact. The battery can slide out downwards past the motor.
Cutting a large hole in the frame to allow battery access can only reduce torsional rigidity, a weight penalty being added to gain that stiffness back with increased lay up thickness perhaps?

Can do that already with the existing motors - see whyte with the bosch gen 4, and specialized with the brose

 

[Sidepod]

Yup the Levo design is nice.

Just to be clear, I have no axe to grind here or preference for any particular bike, just an interest in the different design approaches.