Regen

john61ct said:

MadRhino said:

... The ONLY good reason to power a bike with 2 motors is traction

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Assuming gearing.

If using DD hubs only, 2 motors will enable torque for loads that no single existing motor can handle.

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True, only when you have one of the biggest motors already, and that it is fed close to saturation.

Two 15 lbs motors will not make the power of one that is 30 lbs. Now, if you have a 30 lbs motor already and want more power, it might be difficult to find one that does beat two of them. Yet, a 100 lbs motor can beat 160 hp, and that is much more power than three 30 lbs motors are capable of. The logic is that a considerable part of a motor weight is in the support, and the bigger the motor, the bigger the percentage of it can be copper and magnets.

MadRhino said:

john61ct said:

MadRhino said:

... The ONLY good reason to power a bike with 2 motors is traction

Click to expand...

Assuming gearing.

If using DD hubs only, 2 motors will enable torque for loads that no single existing motor can handle.

Click to expand...

True, only when you have one of the biggest motors already, and that it is fed close to saturation.

Two 15 lbs motors will not make the power of one that is 30 lbs. Now, if you have a 30 lbs motor already and want more power, it might be difficult to find one that does beat two of them. Yet, a 100 lbs motor can beat 160 hp, and that is much more power than three 30 lbs motors are capable of. The logic is that a considerable part of a motor weight is in the support, and the bigger the motor, the bigger the percentage of it can be copper and magnets.

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I was not talking HP (watts) but Amps (torque) specifically.

400lb (500?) heading up a steep 4-mile grade, including maybe standing starts part way. Assume enough battery, at least 72V, 80+ more likely, **heat** is the limiting factor.

Want to **try** to get up over 10mph but needs a lot of help standing on the pedals.

QS273 and biggest FOC possible, with CAv3 preventing overtemp.

Any and all suggestions welcome, other than talking about mid-drives or gears.

Pretty sure I need at least two DDs.

niwrad said:

I think the regen% on CA should be interpreted best as, 'how much larger battery I would have needed', i.e. if you recover 100% of your energy then you would have infinite range, which makes sense.

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I guess you never know what's going to make sense to someone else, but it's probably best to think of it as what it is, the ratio of regen to battery draw. Since it's rarely much of a difference, it doesn't really matter a whole lot, it just comes up once in while when people come in with astounding regen percentages, where the real percentage is still pretty good but a couple percent lower.

So if I run dry and had 15% regen, then without regen I would have only made it 85% of the way home, or I needed a 15% larger battery. Or if I didn't run dry, then I could use X% smaller battery for the same trip

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If you had only enough to go 85% of the way, then you need 100/.85 - 100 percent larger battery, 17.6%.

john61ct said:

I was not talking HP (watts) but Amps (torque) specifically.

400lb (500?) heading up a steep 4-mile grade, including maybe standing starts part way. Assume enough battery, at least 72V, 80+ more likely, **heat** is the limiting factor.

Want to **try** to get up over 10mph but needs a lot of help standing on the pedals.

QS273 and biggest FOC possible, with CAv3 preventing overtemp.

Any and all suggestions welcome, other than talking about mid-drives or gears.

Pretty sure I need at least two DDs.

Click to expand...

I believe that you are underestimating the power of big motors.

I climb 10% at 50 mph, and it doesn’t take long to get there from a dead stop on the slope. That is with a 205, much smaller than a 273, and it doesn’t even get warm doing it. Heat is a problem at 10 mph of course, if the climb is long especially. That kind of low speed is not hub motor territory, unless it is a custom very slow winding.

You don’t need a big motor to do 0-10 mph on a slope, you need it slow, or you need to gear it down. With the average big hub motor, 0-10 can be done in a second, you just don’t want to stay there very long because it is far out of its efficient zone. Order a custom winding, or drive a chain if that is your target speed.

I've been "sharply educated" by the top gurus here that the lower kV makes no difference in this case, higher the voltage the better.

But multiple DD motors will help, given no gearing.

The issue is the 500lbs, and **getting from** zero up past 5-10mph, key is splitting the heat dissipation in half.

Once above 12 or so, then less of a problem, but of course need to plan for worst case, or I'll be pushing it up with my back and legs. . .

One big motor, and 2000w into it, will get 500 pounds up the rocky mountians. Ben there, done it. Talking long hills, and mostly, they max out at 8%. Short hills get much steeper though. Two 1000 w motors will also do it, but I have not personally built that. It was just so much simpler to run a 5304 once I got one.

Lower speed motors are good for going slower that it. Not more torque.

But you can eventually get up a longer steep hill with more load on the bike by using a slow motor. This is talking about overloaded motors, typically a 1000w controller that can't go up 10% very fast with a 400 pound load. Its still overloaded but the slow motor can tolerate lower rpm and gets to the top. There are much better ways to solve the problem, ( like small wheels) but you can get to the top of the mountain with less overheat with a slow overloaded motor than with a fast overloaded motor.

It don't work near as good as a big motor, and give it power. In other words, don't overload it. That's what really works. And then you can carry extra battery and fast chargers, or trailers with panels, etc.

The most efficient bike I ever built for loads up to 400 pounds, used a 500w slow wind DD motor in 20" rim. If I kept the total load down to 300 pounds, meaning no cargo, it climbed mountains with good efficiency. But mostly, it was long range simply because between the small wheel, 48v voltage, and low rpm wind, its top speed was 18 mph. So it would go much farther than my 2000w bike, which I tended to ride 25 mph.

That low speed bike could do a lot more than 400 pounds load on the flat of course. But up the rockies, 400 was as heavy as I tested it.

Yes other factor didn't mention, need big fat tires, most usage off pavement, desert dirt tracks gravel, logging access roads

with fattie tires dunno what rim, but figure 26" outside diameter?

so loses the "gearing" of a 20" wheel unfortunately

john61ct said:

I've been "sharply educated" by the top gurus here that the lower kV makes no difference in this case, higher the voltage the better.

But multiple DD motors will help, given no gearing.

The issue is the 500lbs, and **getting from** zero up past 5-10mph, key is splitting the heat dissipation in half.

Once above 12 or so, then less of a problem, but of course need to plan for worst case, or I'll be pushing it up with my back and legs. . .

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Well, my guess is that you got it wrong. The KV does not make a difference in the power available but:
The KV of the motor does make a big difference if you target 10 mph, for it is making it in the motor efficient zone. With a high KV you would need to run it at 15v to be efficient at that speed, and the Amps would need to be huge to supply the climbing power at low voltage.

I run high KV motors at 24s. The performance is amazing, but the efficiency at 10 mph is very poor.

There are not so many ways to be efficient at low speed. Low KV, low gearing, small wheel. You can try dual motors if you want, they will never give the torque and efficiency of a big motor that is built to be efficient at the speed that you target. The only situation where 2 small motors are better than a big one, is slippery surface.

Sorry did not mean to write kV makes no difference, I know I want lowest winding possible.

The big revelation for me was going to say 72V battery would be better than 48V, even for that crazy-torque need and even if I never went over 15mph as a top speed.

I realize and accept, when the huge torque is required at low rpm, efficiency goes out the window.

Again, the bottleneck is the heat shedding, and I don't see how sharing that across 2 DD motors won't help with that.

But if dogman says the QS273 at 90A will get my 500lb cargo over the Rockies, I'll certainly start out by trying it with one of them first.

You don’t need a 50 lbs motor, unless you really want to climb the rockies all day. But, QS motor is a good idea because they are the most likely to supply the winding that you need within reasonable delay. If you can tune the efficiency zone at the speed that you ride, a 205 will be overkill already. I feed my 205 bursts of 25 kw in acceleration, repeatedly without any overheating. 90A is vey small power for a 30 lbs motor.

A midrive works good on hills regen is only about 8 percent. And needs great torque arms. What motor and controller do you have ?

MadRhino said:

90A is very small power for a 30 lbs motor.

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Battery amps, over 10-20min continuous, at very low rpm?

As long as it is running in its efficient RPM zone, 90A won't overheat a 30lbs motor in 20minutes, because most of the power is transformed into motion. Consider that a motor will not pull that much very long anyway. After the running speed is achieved, the power required to maintain it is much lower. It is the time spent in the inefficient zone that consumes a lot of power, and does make a lot of heat. I am feeding power that could overheat a 205 in 30 seconds, but even when I hold full throttle the motor does pull full power only a few seconds in primary acceleration.

MadRhino said:

As long as it is running in its efficient RPM zone

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The whole point of the use case I've outlined is nowhere near that zone

> time spent in the inefficient zone that consumes a lot of power, and does make a lot of heat

lugging at very very little motion (volts) very low rpm, and very high torque (amps with )

efficiency not even a consideration, a massive struggle just to keep the windings from melting.

Which is exactly why splitting the heat dissipation load is helpful.

Of course in a scenario where speed can rise over 10-12mph, then all worries are over, and the second motor becomes dead weight.

But that doesn't make it less vital, necessary for the worst case.

Maybe, we shall see.

You keep describing exactly the situation where gearing works exceptionally well.

Agreed with gearing.
I mean, if you plan to ride 3 mph on steep hills the hub (s) is not even an option. Would there be 2, the rear one will fry while the front one loses traction. The harder the acceleration or steeper the climb, the less a front motor has traction because the more of the load is on the rear. It is the same reason why the rear brake is useless on hard braking, or steep downhill. This does explain why proper bikes have good power on the rear and good brake on the front.

My guess is that you need a big mid drive, if your overheating worries are justified. But, some just need to go to the end of their idea. It doesn’t cost much to fry a hub. I have fried a good dozen myself before I realized the proper motor size, power, building and riding that are required up the mountain trails. There is a moment when you need to make a choice: either you accelerate quickly out of the inefficient zone, or you build mid drive.

Uhh,, where did I say 500 pounds up the hill? Or geared motor?

Sorry if I wasn't very clear, I only know about what I did, and worked. That was a slow wind 500 w rated DD motor. 9 continent type if you will. And it went 400 pounds, in 26 wheel , and about 1200w max , fine. 500 pounds and the rockies will smoke it.

But yes, while not the very most efficient, two of them running 1200w each, then you get twice the heat dissipation, or half the heat input to each.... And meanwhile, if you do heave 2400w at it, you aint going slow and inefficient anymore.

One thing I never tried, but could be worth a try, is a dd motor in back that runs all day, combined with a geared front motor that runs only up the mountains. Pick a DD motor that goes the speed you want at full throttle. Then when it lugs, hit a horn button that kicks on the second motor.

But really, the big motor worked so good, I just never bothered to try the two motors.