Virtual electronic freewheeling question - direct drive motor drag

[sirensynapse]

As always, more noob questions here. Filling the brain up.
I gather that a direct drive motors' magnets drag when not pedaling. Is that significant? So just lightly pedaling avoids that?
I saw Grin's tech can overcome that by its "virtual electronic freewheeling." Anyone know how much battery that eats?

 

[E-HP]

If you lift the back wheel and twist the throttle and spin up to the speed you'd normally be freewheeling at, and then check the watts, that's approximately the amount that virtual electronic freewheeling will consume.

 

[Elmo]

E-HP's tip is spot on. try spinning the wheel and checking watts to get an idea of power consumption for virtual freewheeling. clever way to estimate it!

 

[neptronix]

Depends on the motor. The bigger, the more drag, generally.

Grin's all axle motor has really low drag and is about 1kw rated. I rode my ebike without a battery for a while, it wasn't too bad, just docked me 1-2mph over my natural speed. It would only need a tiny amount of virtual freewheeling current to feel like a normal wheel.

Grin's RH212 is another story because it has more poles and certainly has higher magnetic losses.

Leafbike 1.5kw ( in reality more like a 2kw rated motor ) has quite low drag for it's size but other motors in it's class tend to have significantly more. Virtual electronic freewheeling would be nice in that situation. I chose to not run it so i'm always feeling the natural behavior of the motor.

Grin's geared hubmotors that have regen could use electronic freewheeling because the drag is significant when it's clutch is locked in place.

 

[gromike]

E-HP's tip is spot on. try spinning the wheel and checking watts to get an idea of power consumption for virtual freewheeling. clever way to estimate it!

When I toggle the baserunner from off to on at 0 PAS on my DD hub motor, the CA3 display reads 1 w.
You can sure feel the difference between pedaling at no power and with that 1w on 0 PAS. Seems like way more than 1w on pedal effort when cogging the motor..

 

[sirensynapse]

If you lift the back wheel and twist the throttle and spin up to the speed you'd normally be freewheeling at, and then check the watts, that's approximately the amount that virtual electronic freewheeling will consume.

Ok, but I didn't buy the motor yet.

 

[sirensynapse]

When I toggle the baserunner from off to on at 0 PAS on my DD hub motor, the CA3 display reads 1 w.
You can sure feel the difference between pedaling at no power and with that 1w on 0 PAS. Seems like way more than 1w on pedal effort when cogging the motor..

You lost me there. You are saying your baserunner is programmed to use virtual freewheeling and it's doing 1w, but it feels like way more?

 

[gromike]

You lost me there. You are saying your baserunner is programmed to use virtual freewheeling and it's doing 1w, but it feels like way more?

Yes.

 

[sirensynapse]

Yes.

Meant to ask too: how much wattage are you using when using a mid-range assist? To compare.
1 Watt sounds impossibly low, indeed.

 

[gromike]

When I'm pedaling at speed on1 PAS it's under 200w. At 0 PAS the controller feeds the motor 1w, and that eliminates the resistance of the DD hub motor due to the magnets cogging as the wheel turns. The bike pedals at 0 PAS just like a regular, albeit heavy, bike.

 

[sirensynapse]

1 Watt still sounds crazy low. Maybe someone smarter than me can give an opine?

 

[99t4]

The cogging (magnetic drag) occurs when unpowered, whether pedaling or coasting. That 1W is just to overcome the cogging loss (magnetic drag) when pedaling unpowered or coasting; it's not providing any assist. Just enough to make it feel like a common non-motor hub.

 

[sirensynapse]

The cogging (magnetic drag) occurs when unpowered, whether pedaling or coasting. That 1W is just to overcome the cogging loss (magnetic drag) when pedaling unpowered or coasting; it's not providing any assist. Just enough to make it feel like a common non-motor hub.

`Ja, I get that, but 1 watt is like what we use to spin a PC fan, and a bike motor's guts are vastly heavier than that.

 

[neptronix]

yeah, to spin a PC fan at thousands of RPM whereas a bike might be coasting at ~250rpm.

 

[sirensynapse]

700 rpm, 1,8 watts, etc. Ja, they are pushing air...so heavier than it seems, I suppose.

 

[Hummina Shadeeba]

Cogging is the pull and push of the magnets in combination with the steel stator you can feel as ratcheting and is not a loss. The more magnet poles the motor has the less it will cog. It will run smoother with less ratcheting but produce more losses as more magnets are producing hysteresis. I guess not more eddies if the same magnet mass n strength.