* * * MOTOR UNIVERSITY (Lab 101) * * *

[xyster]

In terms of electric motors, simple physics throws out the extremes, as you couldn't push enough amps at low voltage to produce a direct drive space shuttle mover. On the other end, tiny high RPM inrunner RC motors still have no trouble being geared down for use in cars, boats, planes etc.

Agreed with present-day tech. With superconductive ~zero-resistance materials, pushing those amps would take fewer volts.

 

[TylerDurden]

Lowell is correct, TD is not. <snip>
If it weren't the case that power is equivalent to acceleration, we would not gain acceleration by only overvolting our motors -- but we do.

Try that without your controller...

:lol:

 

[fechter]

Lowell is correct, TD is not. <snip>
If it weren't the case that power is equivalent to acceleration, we would not gain acceleration by only overvolting our motors -- but we do.

Try that without your controller...

:lol:

When you increase the system voltage the controller can boost the current more at low throttle settings, resulting in more current. Acceleration is a function of thrust, which will be directly porportional to current in a single speed system. Higher voltage allows more current to flow to the motor.

 

[Lowell]

Fechter sinks BS faster than an Exocet missile :lol:

 

[TylerDurden]

Fechter sinks BS faster than an Exocet missile :lol:

I'm not sure I would call Xyster's comment BS; but rather, a logical error.

8)

 

[Lowell]

Fechter sinks BS faster than an Exocet missile :lol:

I'm not sure I would call Xyster's comment BS; but rather, a logical error.

8)

That's your ship sinking, not Xysters.

 

[TylerDurden]

Fechter sinks BS faster than an Exocet missile :lol:

I'm not sure I would call Xyster's comment BS; but rather, a logical error.

8)

That's your ship sinking, not Xysters.

Think so?

My reading of Dad's post:
Overvolting only aids acceleration if a controller converts the V to A.

eg. Without a controller, more V only gets you higher RPM.

You need CURRENT, torpedo-breath!

8)

 

[xyster]

Without a controller, more V only gets you higher RPM.

Without more amps, more V gets you the same torque at a higher RPM -- hence more power and better acceleration even if there's no controller in between (think: with same amps, more V gets you to a higher RPM in same amount of time it got you to a lower RPM at the lower voltage. That's better acceleration.)

The controller conversion fechter mentioned simply adds to the effect.

 

[TylerDurden]

with same amps, more V gets you to a higher RPM in same amount of time it got you to a lower RPM at the lower voltage.

Same amount of time??

How so, if you got no addn'l torque...

 

[xyster]

with same amps, more V gets you to a higher RPM in same amount of time it got you to a lower RPM at the lower voltage.

Same amount of time??

How so, if you got no addn'l torque...

Go play with the 4qd acceleration calculator for a few minutes.
http://www.4qd.co.uk/faq/current.html
Plug in anything for the variables, then switch between 48 volts and 24 volts and watch the current necessary to accelerate in X seconds be half at 48 volts of what it is at 24 volts. The calculator also 'splains the math.

See where it says "motor current needed for this acceleration"?

 

[TylerDurden]

Plug in anything for the variables, then switch between 48 volts and 24 volts and watch the current necessary to accelerate in X seconds be half at 48 volts of what it is at 24 volts.

Only if you keep the duration of acceleration constant.

If you change the accel time (RPM) to correlate w/ the change in V, there is no increase in current.

Conservation of energy & all that...

 

[xyster]

Plug in anything for the variables, then switch between 48 volts and 24 volts and watch the current necessary to accelerate in X seconds be half at 48 volts of what it is at 24 volts.

Only if you keep the duration of acceleration constant.

Duh! That's what "X" seconds means. Pick an acceleration and keep it the same while massaging the other variables. And the physics is the same controller or no controller. Do you really believe that if you directly connected your bike's motor to 100 volts and 10 amps, it would accelerate at the same pace as if you directly connected it to 10 volts and 10 amps?
Why do think the venerable speed and power calculator for regular bikes (no controller) uses "Power" (volts X amps) to calculate hill-climbing ability rather than "torque"?
http://www.kreuzotter.de/english/espeed.htm
Is not hill-climbing ability the same as acceleration since gravity is expressed as an acceleration (9.8m/s^2)?

 

[xyster]

Another question:
Look at where peak torque is on every motor in every configuration on the hubmotor simulator:
http://www.ebikes.ca/simulator/

It's at zero speed, right?

And torque decreases between zero speed and top speed, right?

What does your intuition tell you:
Is peak acceleration near the point of peak torque (at 0kph)?

Or is peak acceleration nearer the point of peak power (the redline)?

 

[TylerDurden]

Is not hill-climbing ability the same as acceleration since gravity is expressed as an acceleration (9.8m/s^2)?

Ja, man. Dats why we like to know slope for safe's crippled controller.

Call me a retard.

But...

2X the voltage gets you 2x the RPM, not 2X the torque.

Conservation of energy, blah blah...

The reason the 4qd calc shows .5x the current, is 'cause it does not 2x the RPM.

 

[TylerDurden]

Another question:
Look at where peak torque is on every motor in every configuration on the hubmotor simulator:
http://www.ebikes.ca/simulator/

It's at zero speed, right?

And torque decreases between zero speed and top speed, right?

What does your intuition tell you:
Is peak acceleration near the point of peak torque (at 0kph)?

Or is peak acceleration nearer the point of peak power (the redline)?

Without the Socratic exercise... where ya goin here?

 

[TylerDurden]

Do you really believe that if you directly connected your bike's motor to 100 volts and 10 amps, it would accelerate at the same pace as if you directly connected it to 10 volts and 10 amps?

Pretty much...

A better example might be 1000V vs. 100V, but yeah. Until somebody shows me some math that proves otherwise.

 

[TylerDurden]

Why do think the venerable speed and power calculator for regular bikes (no controller) uses "Power" (volts X amps) to calculate hill-climbing ability rather than "torque"?

As far as I can tell, the 'zotter uses watts to describe power. Perhaps since horsepower would result in fractional (decimal) results.

Cyclists are more concerned with energy expenditure over time, rather than with rotational force.

I know I am... but I'm a piss-poor cyclist these days.

:lol:

 

[Miles]

Cyclists are more concerned with energy expenditure over time, rather than with rotational force.

Yeah, who needs gears...........

 

[TylerDurden]

Cyclists are more concerned with energy expenditure over time, rather than with rotational force.

Yeah, who needs gears...........

If ya got a hubmotor... :lol:

 

[Miles]

Cyclists are more concerned with energy expenditure over time, rather than with rotational force.

Yeah, who needs gears...........

If ya got a hubmotor... :lol:

:lol:

 

[xyster]

Without the Socratic exercise... where ya goin here?

I give up. Lowell, Safe, Fechter, me & now Socrates all regard you a hopeless case....on this point at least.

 

[TylerDurden]

I give up. Lowell, Safe, Fechter, me & now Socrates all regard you a hopeless case....on this point at least.

Sheesh. I thought ya wuz good for a few more rounds than that...

Although, bringing intuition into the picture was almost as weak as safe's absurdities.

Simply show me where increasing volts, without current multiplication by a controller, increases acceleration... I'm not too proud to be anonymously wrong... :lol:

 

[xyster]

Simply show me where increasing volts, without current multiplication by a controller, increases acceleration... I'm not too proud to be anonymously wrong...

You mean Tyler Durden isn't your real name? I'm shocked. Xyster is my real name.

I'll have to think about how else to approach substantiating this point since neither one of us is likely to directly connect our batteries to our motors and perform time trials. And even if I did, you'd probably suppose better acceleration was caused by the higher voltage pushing more amps...so we'd have to develop a non-pwm current limiter.
One more Socratic query: if 100 volts 10 amps accelerates your bike at the same rate as 10 volts 10 amps (as you said you thought it would), what happens to all the extra power (90 volts X 10 amps = 900 watts had to go somewhere!)? I'm saying the extra wattage (power) goes to faster acceleration.

 

[TylerDurden]

Xyster is my real name.
One more Socratic query: if 100 volts 10 amps accelerates your bike at the same rate as 10 volts 10 amps (as you said you thought it would), what happens to all the extra power (90 volts X 10 amps = 900 watts had to go somewhere!)? I'm saying the extra wattage (power) goes to faster acceleration.

Man... I woulda lost a bet that you made that name up. :?

Ja, I'll contend that if 10V gets you to max 100rpm in 10sec, 100V will too... but the 100V test will continue to rise in RPM to 1000rpm or whatever.

 

[Lowell]

The 90v motor circuit would need a higher wind to keep current the same as the 10v circuit without the benefit of a speed controller. My money is on 90v for the win...