"User Friendly" Motor Physics

[safe]

Torque at stall is basically a "space heater" though. You lose just about everything to get the torque.

What I'm trying to do is to calculate the effects of all these parameters to see what is really the best way to go. I think the "ideal" would be:

Motor Size - Legal Limit of Horsepower (whatever that is in your state)

Gears - To give better efficiency, better hill climbing, better top speed. (which might get you into trouble)

Good Aerodynamics - So you don't throw money to the Wind.

Good Handling - Good Tires - Good Brakes

Of course, if I committed to moving up into the "motorcycle class" then all these restrictions could be avoided. But then you need all kinds of legal crap and it gets complicated.

 

[Leeps]

I do agree with you on what you said there.
When it comes to picking a motor there is more to efficiency than just size, so be careful, but in general your right, unless somebody does something stupid like picking a 1200 watt motor to drive a 300 watt load ( something as simple as gearing for a too low top speed).
Joe

 

[xyster]

Any other positives?

A few come to mind:

-In general, hubmotors are quieter.

-Hubmotors can be waterproofed more easily.

-Bicycle chains, gears and such (I'm surmising) may not in general handle the same power (2.5-5kw) commercial hubmotors can (of course with gears, they don't so much need to...but with light lithium batteries, good ol' inefficient brute force can be used to overpower gear driven shifting systems)

-Hubmotor installation is much simpler, also allowing simple hubmotor swapping experiments.

-Small hubmotors are more stealth than bb drives, etc...

-Hubmotors can be run front, rear, or both simultaneously far more simply than other systems.

-Side-by-side hubmotors can obviate the need for differentials on trikes and quads.

-Simpler (w/o an extra freewheel) chain driven systems do not coast, but require the user to peddle whenever the bike is in motion. Not so with hubmotors.

-No required shifting to distract one's concentration.

 

[safe]

No required shifting to distract one's concentration.

Hmmmmm... turn a negative into a positive I guess...

Moving on to other thoughts:

What about two hub motors?

One in front that is geared for top end speed and one in rear to deal with a 15% grade. They could both be running at the same time, but one would "overlap" the others powerband. When one is in a "weak area" the other could be in a "strong area" of their powerbands.

Anyone tried this?

You could use a lighter weight hub motor on each and it would help to resolve the "center of balance" problem with a 25 lb rear hub.

 

[safe]

1492

No, I don't plan to talk about Christopher Columbus or anything historical. The bottom line for me is that I'm going to want to obey the laws here in my state which allow up to two horsepower as the absolute maximum. 1492 Watts is two horsepower. (1500 Watts is "close enough")

Gearing might get me into trouble because the legal limit is supposed to be 30 mph here, but I think it's going to be easier to talk myself out of a gearing related issue than a motor size issue.

So I'm just thinking that for issues not related to technicalities I can't go in the direction of the 72 Volt 35 Amp machine because that produces:

2520

...watts of power. That's not just slightly over the limit that's 69% over the legal limt. At that point your bike is a MOTORCYCLE. (3.4 hp)

So when you ask a different question you get a different answer. In order to obey the laws and get the performance one desires the better approach is to use gearing. In a world without restrictions I think the "unrestrained" hub motor is quite possibly the better approach.

 

[xyster]

2520

...watts of power. That's not just slightly over the limit that's 69% over the legal limt. At that point your bike is a MOTORCYCLE. (3.4 hp)

50
...miles per hour is 60% higher than your stated legal limit of 30 mph!
----------------

Well, some of us are more restrained by reason, and consideration for others, than the strict, and often arbitrary and backwards letter of law.

I don't go the speeds you wrote you wanted to. I use the power to get up steep hills more easily, and, when warranted, accelerate away from trouble (like unrestrained pit bulls) more safely.

In light of your stated desire to obtain 50mph on your ebike, and tackle tight turns at high speeds, your concern for wattage limits does not appear internally self-consistent.

All my future projections were for a top speed around 50+ mph and the ability to climb a 15% grade and they look attainable with an 8 speed internally geared hub.

I'm seriously thinking this [hubmotor] won't do it for me...

 

[mr.electric]

If you really want to stay under 1500 watts I would get a curry s-1000 or i-zip - 1000 watt 36v motor and run it at 48 volts.
you will get about 1333 watts from a cheap high torque motor. This is a rare earth magnet motor with cooling fins that costs $80 new. It will bolt up to any curry bicycle or scooter. Of course you will need the right controller and batteries. This is an i-zip 1000 watt 36v motor with curry bicycle gear head.

 

[safe]

I have theory about the "PWM Current Warping" effect. (Buck Converter)

Since the numbers in the Simulation model place a value of roughly 50% as the percentage of the current that is actually supposed to get through and help the motor with extra torque I have a theory about why it's roughly that way.

When you have a waveform you are basically dividing time up into "on" and "off" sections. This is the "duty cycle" for the controller. When you take an average of "on" and "off" current bursts and most of this is in the 50% equivalent throttle setting (50% on/50% off) the result would an average of the "highs" and the "lows" so you end up getting 50% of what you theoretically could get. I would guess that the effect is probably more efficient at higher voltage than lower because at some point the "pump" loses pressure and can't move the voltage fast enough. I know that the actual electrical properties are more complex than that, but 50% seems like a realistic value to me.

"Good enough"

It's for horseshoes, hand grenades and PWM controllers?

 

[Leeps]

please google buck converters
Joe