New power/speed allowable performance envelope

[matthewslack]

It'll never happen, but the following would highly suit my style of low energy, long distance touring.

1. Actual delivered power not a thing of particular concern, provided speed is not above 25km/h.
2. Absolute cap of 250W on delivered power above 25km/h but otherwise no assistance speed limit.

All subservient to the needs of more vulnerable users of shared routes, of course.

I've reached the limit of what an upright riding position can do, and when I get to the much better aerodynamic performance of my forthcoming e-trike, I think I may find less benefit to daily averages than I would like under the current rules.

 

[saneagle]

Which 250w? How are you going to measure it? How are you going to control it?

 

[matthewslack]

For a hub motor I'd measure it by telling the controller all about the motor, and letting it make a calculation from easily measured input V and I.

For a torque sensored mid-drive, it already knows from torque and rpm of the crank, so just needs a reasonable allowance for drivetrain efficiency.

For my experimental work with a torque sensored mid-drive whose inner workings I don't have direct access to, I would just apply a blanket assumption about likely efficiency, and combine that with easily measured input V and I.

 

[saneagle]

For a hub motor I'd measure it by telling the controller all about the motor, and letting it make a calculation from easily measured input V and I.

For a torque sensored mid-drive, it already knows from torque and rpm of the crank, so just needs a reasonable allowance for drivetrain efficiency.

For my experimental work with a torque sensored mid-drive whose inner workings I don't have direct access to, I would just apply a blanket assumption about likely efficiency, and combine that with easily measured input V and I.

With a crank motor, you can use the gears to keep the motor running at the rpm that you based your calculation on, but you can't do that with a hub motor. How will your controller know what torque there is at the crank?

 

[matthewslack]

With a crank motor, you can use the gears to keep the motor running at the rpm that you based your calculation on, but you can't do that with a hub motor. How will your controller know what torque there is at the crank?

Scenario 1 above. It doesn't need to know. Treat the controller and motor as a unit, and allow the controller to understand the performance curves of the motor. Then measuring input V and I (and of course rpm, sorry I left that out before) allows output power to be calculated with sufficient accuracy.

 

[saneagle]

Scenario 1 above. It doesn't need to know. Treat the controller and motor as a unit, and allow the controller to understand the performance curves of the motor. Then measuring input V and I (and of course rpm, sorry I left that out before) allows output power to be calculated with sufficient accuracy.

Hardly anybody on this forum can understand the performance curve of the motor, whatever that is, so how is a dumb controller going to do that, or are you going to incorporate DeepSeek AI into it?

You have the other problem that the battery voltage is constantly changing too.

 

[matthewslack]

Controllers don't have to be dumb.

 

[Bikes4two]

How will your controller know what torque there is at the crank?

..... with a bottom bracket torque sensor as you can get with some of the kits from the likes of @Woosh (and pre-built ebikes fitted with the Mahle X20 ad X30 motors now have torque sensors in the BB - clearly a growing trend).

Just saying........

 

[saneagle]

..... with a bottom bracket torque sensor as you can get with some of the kits from the likes of @Woosh (and pre-built ebikes fitted with the Mahle X20 ad X30 motors now have torque sensors in the BB - clearly a growing trend).

Just saying........

We're not talking about pedal input torque, and the torque sensor can't measure the output torque.
Just saying........

 

[Sturmey]

1. Actual delivered power not a thing of particular concern, provided speed is not above 25km/h.
2. Absolute cap of 250W on delivered power above 25km/h but otherwise no assistance speed limit.

I wonder would just an ordinary low rpm motor work for you as the power naturally tapers down at about 20Km/hr due to back EMF. I fitted one of the original (210 rpm) Yose 250W front and it worked like that and is broadly similar to what is modeled below. You could experiment with the model by increasing/decreasing rpm/V setting and controller current setting etc.
PS. The red line below is total power output in mechanical watts.

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

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