How does torque factor into drawing power from the motor?

[GrayFox]

Most of the discussions that I have read on this forum about how the power is supplied to the system seem to involve using a high cadence.

I have reached a certain age where I can no longer pedal at a high cadence. My average seems to be stuck in the mid 50's where I can average 14.4-16 mph... Basically I have become a 'grinder' instead of a 'spinner'.

I have noticed that when I go up a hill that it feels like the harder I mash the pedals that it feels 'easier'.

ie More Torque Means More Power. Is there any documentation to support this idea?

 

[dodgeman]

Just the general reaction I get from riding my Trek is the harder you work the more power you get from the motor.

 

[retiredNH]

Torque and power are two different things. To make things even trickier, different drive systems will have different torque curves vs pedal RPM, wheel RPM, crank torque and so forth. Back to your original question, power = torque x distance. Translated, power is torque roughly times pedal RPM. But this doesn't translate that easily to how your bike feels, so be glad it works for you as it is!

 

[PedalUma]

@GrayFox,
Have you tried a different pedaling technique? This makes for a swimming-like motion. Torque sensor motors love it. I read your opening post and understand but still you might try this. If you imagine the right pedal positions like hours on a clock face, noon would be up at top dead center. The technique I suggest puts the focus on 7 to 10. Try sweeping back and up. Range, Power and Smoothness will all be greatly enhanced. One of the things it does is make the controller less spiky. Look for some videos on How To Pedal Like a Pro.

 

[Stefan Mikes]

@GrayFox: Talking only on torque sensing is some oversimplification here. Specialized e-bikes use several sensors to determine the necessary assistance. What is actually amplified, or boosted is your leg power. You can actually either mash or spin the cranks to much the same effect: either high leg force at low cadence, or low leg force at high cadence can produce exactly the same leg power.

The power you deliver to the cranks will be multiplied by the controller, and the proper amount of electricity will feed the motor to assist you. The more power you input the more assistance you will get from the motor. In Turbo mode, you can actually max the motor out if you pedal very hard.

So, whichever way you deliver your leg power to the cranks, the more rider's power the more battery charge used at the same assistance level.

However, there's also motor performance curve. Mid-drives become efficient at cadence above 70 rpm (new Vado/Como/Tero all show you the optimal cadence on the Mastermind display).

The technique Uma described is very good to practice higher cadence. I concur. Downshifting more can help getting higher cadence, too.

 

[retiredNH]

@GrayFox: Talking only on torque sensing is some oversimplification here. Specialized e-bikes use several sensors to determine the necessary assistance. What is actually amplified, or boosted is your leg power. You can actually either mash or spin the cranks to much the same effect: either high leg force at low cadence, or low leg force at high cadence can produce exactly the same leg power.

The power you deliver to the cranks will be multiplied by the controller, and the proper amount of electricity will feed the motor to assist you. The more power you input the more assistance you will get from the motor. In Turbo mode, you can actually max the motor out if you pedal very hard.

So, whichever way you deliver your leg power to the cranks, the more rider's power the more battery charge used at the same assistance level.

However, there's also motor performance curve. Mid-drives become efficient at cadence above 70 rpm (new Vado/Como/Tero all show you the optimal cadence on the Mastermind display).

The technique Uma described is very good to practice higher cadence. I concur. Downshifting more can help getting higher cadence, too.

This is true for quality mid drives, but may not be true for other systems, especially hub drives.

We don't know what kind of system the OP has, or what brand, which might tell us how sophisticated the drive system and its controller are.

 

[Stefan Mikes]

We don't know what kind of system the OP has, or what brand

It's Vado SL 5.0 Have you noticed we are in the Specialized sub-forum?

 

[SoCalDave]

In response to the OP's question, in terms of basic physics, power is simply torque times RPM (the correct units must be used when doing this calculation). In an internal combustion engine (ICE) in an automobile, the engine produces a certain amount of torque at a certain RPM. The graph of this is the torque curve of the engine. If the torque curve were close to flat, then an engine operating at a higher RPM will have a higher power output.

Now, to apply this to ebikes, I am most familiar with Bosch mid drive ebikes. The sensors measure your cadence (RPM), and measure the torque you are applying to the pedals, and can calculate your power output. Software then decides how much assist that the motor will provide. The amount of assist will depend on your cadence and how much torque you are applying to the pedals, and the assist level you have set (ECO, TOUR, SPORT, TURBO). The thing I like about the Bosch software and hardware is that it feels very natural if you are coming from an early Dylan (non-electric) biking background. It will reward you for spinning and being in the right gear. If you are on an early Dylan bike and are in a high gear, and try to climb a steep hill, your cadence will be too slow and the torque required will be too high - especially bad for aging knees. You want to be in a low gear and spin. That doesn't mean that you have to spin at 120 RPM, but it does mean that the system won't work well if you are only pedaling at 40 RPM.

 

[Stefan Mikes]

an early Dylan bike

Worth every cent!

 

[PedalUma]

I love the Dylan reference. In 1965 he plugged in at the Newport Folk Festival. Many purists called him a tarator. I think of better electric bikes as being acoustic/electric. They still feel like a bike. Just amplified.

 

[briandmunn]

Sweet……Al Kooper, and Michael Bloomfield as well.

 

[Pork Rind]

I think of better electric bikes as being acoustic/electric. They still feel like a bike. Just amplified.

Judas!