High Torque Hub Motors

[Lurkin]

I don't think you understand what Chalo has pointed out.

Wheel size choice is totally preference dependent. You can choose to put the needs of the operation of the bike first, or your own preferences without considering the motors preference. In my case, it definitely isn't ideal to go down a size. I.e. the motors efficiency is only one attribute to consider and depends on builder preferences to choose its priority.

For example, if clearance is an issue, larger wheel sizes are ideal. This is putting the needs of the user first, not the efficiency or preference of the operation of a motor/electric bike set up.

In any case, this thread has already had it stated often enough that smaller wheels = more torque, we get it. Why not try and answer some of the other questions posed?

 

[999zip999]

Well not.everybody has a battery that can deliver 100amps and please don't push lipo. Me no worry me run A123 20ah.
Lurkin I like running my 5t so fast the motor emf is meet and it's amp demands are lower and I top out at 38 miles per hour as fast I want to go on a bicycle. But 25mph up hills.

 

[macribs]

I would melt the 3t 100amp on the beach in soft wet sand faster. How has a 36v 100 amp sinewave bike size controller ? And when will they sell 8ga. Thru the axle wire hubs.

If you melt a 3T in wet sand maybe your problem is not the winding but the wheel size? If you know you will need to run slow speed with high torque a DD hub motor is not your best motor choice in the first place, maybe better to use mid drive? But if we stick to hub motor, you can ease the working condition for the motor by choosing smaller wheel diameter. 17" or even 16.

I think it's funny how clueless your advice is here. Do you think a small wheel behaves the same way on sand as a larger one? It will bog down more deeply, more than negating any motor-specific benefits of the smaller wheel.

That's sort of emblematic of the problem with a lot of the big-motor hot rod bikes I see around here. Y'all are adapting the bike to do what's good for the motor instead of adapting the motor to do what's good for the bike. You end up with a fast, powerful bike that sucks. An American motoring tradition brought to the e-bike world!

Well back in the days we used to play in wet sand down the banks of a local river, some of us on 125 cc dirtbikes with 17 or 18" in the rear and some used those kids sized 80 cc dirt bikes. IIRC those used 12" wheels. And guess what, because the riders often was lighter and the bike lighter as well even those tiny 12" wheels did well on the sand of the river banks. Even high marking a steep sandy fall to the riverside on dry powder sand those 12" wheel could climb almost as high as the 125's.

Remember higher RPM combined with tires made for sand will propel you forward with enough force so you don't get bogged down.

 

[macribs]

I don't think you understand what Chalo has pointed out.

Wheel size choice is totally preference dependent. You can choose to put the needs of the operation of the bike first, or your own preferences without considering the motors preference. In my case, it definitely isn't ideal to go down a size. I.e. the motors efficiency is only one attribute to consider and depends on builder preferences to choose its priority.

For example, if clearance is an issue, larger wheel sizes are ideal. This is putting the needs of the user first, not the efficiency or preference of the operation of a motor/electric bike set up.

In any case, this thread has already had it stated often enough that smaller wheels = more torque, we get it. Why not try and answer some of the other questions posed?

You might be right and if so, my bad. English is not my native language and sometimes things get lost in translation. What I tried to point out is that "looks" should not be the #1 focus point when building an ebike for off road use. Sure those 26" looks great, but if you get more with less wheel why not harvest the benefits? At least if you do great part of riding in the sand, your focus should be propulsion over look. One thing to keep in mind is that if you choose a sturdy m/c rim in smaller diameter you can also get real sand tires made for dirt bikes. Wider and much more grippy then your 26" mtb tire. Better propulsion with more torque, higher RPM and much better traction then what a mtb tire can deliver.

 

[John in CR]

One last time differently wound motors are still the same motor. Assume same battery capacity and capability. Also assume same total copper wrapped around the teeth with one motor having twice as many turns as the other. Now let's call the battery a pair of 36V packs. With the slow motor you connect them in series for 72V and with the fast motor you connect them in parallel for 36V. In the slow wind motor the copper is half as thick and twice as long, so it's resistance is 4X the faster motor. The faster wound motor requires double the current for the same torque as the slow motor, and the slow motor requires double the voltage for the same speed as the fast one.

The battery cells of both each see exactly the same current, so neither is more stressful for the battery. Yes, the 36V has to deliver twice the current to the fast motor, but there are double the cells in parallel 999zip999.

Heat is also the same in both motors. Yes copper loss goes up by the square of current, but resistance is 1/4 for the faster wind motor.

So what's the difference in this example. As far as the motor is concerned there is no difference. They have the same torque, speed, efficiency, heat generated, maximum torque potential, hill climbing ability, hill climbing efficiency, etc. The slow wind motor is less flexible going forward, because it's about shot it's wad in terms of power speed potential due to practical voltage limitations. It's also more prone to heat failure, because it's easier to feed it too much current.

Now let's look at the differences in the system outside of the motor. Since the fast wind motor needs twice the current it requires a beefier controller as wiring. While that cost more, getting double the current capacity is cheap and easy compared to a few years ago. In the caparison that's partially offset by the fact that a higher voltage controller for the slow motor adds cost. A higher voltage BMS also costs more and is more complex with double the failure points. Higher voltage chargers cost more. Precharge resistor circuitry becomes mandatory instead of not really needed. Other parts like lighting, horns, etc. are far less common, so you pretty much need a DC/DC converter. High voltage also comes with higher risk of electrocution and fire.

As far as tire size goes, Macribs was 100% correct. Smaller diameter wheels on a hubmotor are especially beneficial in tough conditions like soft sand. Whatever small difference, if any, there is in rolling resistance is more than offset by the tremendous reduction in heat for a given forward thrust. eg In high load conditions like riding in soft sand or climbing hills (the kinds of things that overheat hubbies) a hubmotor makes almost 50% less heat with a 20" diameter wheel than with a 26" wheel for the same amount of forward thrust. When using a hubmotor, instead of approaching wheel size as just a "personal preference", you're far better off using as small a wheel as you can live with.

 

[dogman dan]

Definitely dumb to choose the slow motor, then up the current and the voltage to get the same speeds as the fast motor. I did learn that the hard way, as John pointed out, by overheating quite a few motors. Now I run the same motors on less power, and end up with a good setup for going slow.

Choose a slow motor when what you want is to go slower. A good example of this is the trike kit. Those adult trikes are dangerous as hell above 15 mph, so the trike kit uses a slow motor primarily to limit speed to 15 mph or less. We could limit speed by limiting power, but that would result in poor performance up hills. With the slow motor, we can limit speed, but not limit power to less than 750w. This works better for that specific situation than having a jerky speed limiter kick in, or just having a lame 250w setup.

So choose a slow motor ONLY when the specific situation makes it a good choice. 90% of the time, the faster motor is best. Only a few situations call for the slower motor, and that choice does result in losing quite a bit. You add this, subtract that. choose the slow only when the total ends up on the plus side. For most bikes, it's a far better choice to get a faster wind geared motor, than a slow dd or geared motor.

And when you really need that torque, well, the mid drives are coming hard, and they get better every year. Ride the Bosch if you want to really be impressed with the torque they get out of 350w.

 

[teslanv]

Now let's look at the differences in the system outside of the motor. Since the fast wind motor needs twice the current it requires a beefier controller as wiring. While that cost more, getting double the current capacity is cheap and easy compared to a few years ago. In the caparison that's partially offset by the fact that a higher voltage controller for the slow motor adds cost. A higher voltage BMS also costs more and is more complex with double the failure points. Higher voltage chargers cost more. Precharge resistor circuitry becomes mandatory instead of not really needed. Other parts like lighting, horns, etc. are far less common, so you pretty much need a DC/DC converter. High voltage also comes with higher risk of electrocution and fire.

This is the very crux of the issue, John.

Doubling the current capability of the controller from one system to the other is NOT as simple or inexpensive as you suggest. (And I could care less if you think I have overpriced Controllers. It's not the point.) This is true for any two similar controller options. We are talking about a 50A Controller vs a 100A controller here. A 12FET IRFB4110 controller vs a 24FET IRFB3077 Controller would be an appropriate comparison. Please enlighten us as to your recommendation for two options here.

As far as DC-DC converters go, I think this is irrelevant. You still need one to drop down from 36V to 12V/3.3V, or you can use a product like Grin's Lighting, which is good from 12V to 100V.

http://www.ebikes.ca/shop/ebike-parts/lights.html

Doubling the conductor sizes is no simple task either. 10-12AWG is cheap, easy and very suitable for 50A systems, while you have to step up to 8AWG or maybe even 6AWG to keep the same electrical efficiency at 100A. You will have to swage those 6AWG conductors, which is a PITA, and trying to squeeze them into the controller box and solder them onto the controller board... forget it. You would likely need a controller that has screw terminals, in that option.

BMS systems is a topic unto itself. There are few really good BMS systems. Most of them suck, whether they are 10S or 20S. Many will choose a battery set-up exactly as you had described, two 36V batteries in series, which by my math, means you have the same number of balance connections to fail, compared to using two 36V batteries in parallel. Or they are building a custom 36V high-current battery, which would have it's own challenges.

High-Voltage = High danger. Sure, there is a little more risk here, but remember that it's not voltage that kills, but total power. Even a Slow-Wind Set-up is under 100V, usually.

https://en.wikipedia.org/wiki/Electric_shock

Your theory about motor windings (with equal copper fill) being the same is fine. I agree with all of that. But to say that a person could and SHOULD always build with the faster motor is just bogus. Building a 50A system vs a 100A system is "apples and oranges". That's where my problem with your argument lies.

 

[999zip999]

So I need a back up motor to go with my 72v A123 20 ah and 12fet 40a controller. Just as well go faster in a 26in mtb rim. A 3t muxsu 3,000 at 3,200 watts using that battery and controller combo. Or by the A123 20ah battery as it can be split to 12s or if what ? A 36v 100 amp sinewave controller ? Never seen one hear. ??? Price ? Size ?
Or better ? A 1,500 35mm for weight. Maybe go there as it is a bike ?
Don't get wrong I love my 3,000 but maybe a 1,500 or 35mm might be.easier on my rim or lighter batteries and lose some weight. I weight less then you John.
P.S. finger trying and no eyes 99cent store glasses.

 

[Lurkin]

I do not understand what you mean.

 

[999zip999]

Looking for JohnCr wisdom on motors to match my battery and controller combo. Because I can go 36v 40ah or 72v 20 ah.

 

[jmz]

In order to do that, you really need to know:

Proposed wheel diameter
Target top speed
Target top power
Available motor kV selection

The proposed wheel diameter will tell you the rpm at your desired top speed. You want to be able to deliver close to maximum power at this speed. Using the motor kV, you can find the estimated no-load RPM for each combination of kV and dc voltage. Using a rule of thumb of 70-80% of the no-load speed, or better yet, the dyno charts, you can work out where the max power rpm is, and compare this to your target top speed rpm, for the available motor kVs.

If your calculated max power rpm for a given wind/battery is less than your target, you're just starting to cut into top speed (assuming your estimated wind/hill loads are right), leaving you just starting on the power downslope, which is a pretty good place to be.

If your calculated max power rpm is above this target, then your wind is unnecessarily fast for the application and you are burning more power in your FETs and phase wires than is necessary.

edit: make sure to also allow for battery sag and state-of-charge.

 

[999zip999]

Funny o.k.

 

[dogman dan]

My wisdom, if you can call it that, would be pick the faster, or at least "normal" rpm motor. Only choose the slow motor if you had the specific need for it, such as you want to ride WOT with lots of potential power, yet still be going slow.

Except for those situations, it is dumb as hell to choose the slow motor.

 

[999zip999]

EFM is efficiency ? Plus ? State of grace.

 

[John in CR]

Looking for JohnCr wisdom on motors to match my battery and controller combo. Because I can go 36v 40ah or 72v 20 ah.

My wisdom is for you to have a very happy new year! As far as ebike specific, my advice is to let go of the myth in all its different wording and incarnations.

 

[Mundo]

This discussion has been an interesting read.

I know skyeg3 was wishing John would suggest a particular motor, controller and battery.

However, this is a decision you'll have to make.

I have two Mundo's. one is a mid-drive V4, with a geared motor (Mac 10T 48 VDC 20AH Ping). This bike works great and it has allot of torque for pulling loads (trailer and such), it is 4 or 5 years old, remains very practical

The other Mundo V2, is also a Mac 10T mounted in a wheel, this bike is underwhelming (36 VDC 40AH Ping). Sometime early spring, this bike will be re-done with direct-drive 72VDC 20AH.

I tell you this because we've all made decision on what to buy and sometimes it doesn't work as well as we thought.

My best advise, spend time with Motor Simulator at Justin's site!

http://www.ebikes.ca/tools/simulator.html

Look for performance, torque and efficiency

 

[dogman dan]

When I tested a motor nearly identical to the Mac 10t, on a heavy cargo bike towing a heavy load, it fried itself on the mountain I use to kill motors. My test was 48v, but bottom line, not enough power to haul a 400 pound total load up a miles long 7% grade. It stalled to 8 mph, then fried. The 10t is not really a slow motor btw, just the slower end of the normal speed rpm scale. I doubt a 12t would haul that much load up the mountain either.

Bottom line on your mundo, you really need more power to be anything but underwhelming with a hubmotor and 26" wheel. I'm not sure you need that much volts though, unless you want it to go 35-40 mph. Same dd motor on 48v 40 amps will be a more safe to ride top speed, and still have the 2000w or so you need to make a heavily loaded long tail cargo bike fun to ride. A larger motor, of normal wind, is what you need. I have an old 5304, but the newer HS or HT clyte is near ideal for big cargo bikes.

And yeah, HT stands for high torque, which is total bullshit. But if you want the bike to go less than 30 mph, then choose the slower wind HT. I'd prefer the HS where I live, since 30 mph is completely legal here.

Choosing the HT, then running it at 72v, gets you nothing, it's dumb.

 

[999zip999]

How about a leaf 1,500 watt motor 35mm. Or a new muxus 1,500 watt 35mm. I hate the crystalyte 3525 and 3540 has funky axle and wires.

 

[cwah]

How about a leaf 1,500 watt motor 35mm. Or a new muxus 1,500 watt 35mm. I hate the crystalyte 3525 and 3540 has funky axle and wires.

But I suppose for torque you need thicker stator. So 45mm or more should be the way to go?

 

[999zip999]

JohnCR much love. I tried working with you and a 36v battery can't get the watts . Remember I have two 36v batteries so 36v or 72 v. I can only get the wattage at 72v. As Im not chopping it apart for a 48v. So maybe the compromise is 1,500 35mm @ 72 v 60 amp 4,600 watt with temp sensor 4t ?

 

[John in CR]

JohnCR much love. I tried working with you and a 36v battery can't get the watts . Remember I have two 36v batteries so 36v or 72 v. I can only get the wattage at 72v. As Im not chopping it apart for a 48v. So maybe the compromise is 1,500 35mm @ 72 v 60 amp 4,600 watt with temp sensor 4t ?

You obviously haven't worked with me or you'd know that your two 36V packs in parallel will deliver exactly the same watts possible as they can in series for 72V. Just like doubling the motor Kv, arranged as 36 the electric pathway is twice as thick and half as long for 1/4th internal resistance to allow double the current with the same heat. As always of course, the right motor and gearing are required, so you'll need to stop purchasing whatever greatest thing since sliced bread all the noobs are buying, and instead look at your system as a whole so you can make absolute reliability a priority.

 

[madin88]

I don't understand your point about the end windings if it's still the same number of strands around each tooth.

John in CR, you are of course correct about the torque production efficiency equivalence of the different winds.

There is a minor caveat around the construction details of the end windings and the phase wires; these will lead to variance around the nominal motor constant/torque efficiency depending on the vagaries of the construction and the fixed contribution from the phase wires. Based on the factory-supplied data from QS motor (including supplied resistance data, not measured by me), I calculated a consistent trend towards slightly lower efficiency in the faster winds:

https://imgur.com/g8Zkqql

If you subtract the contribution from the phase wires (I believe these are best properly regarded and analysed as being part of the inverter/battery system rather than the motor), what you are really left with is variations in the *impedance* of the motor. The effective winding inductance goes up with the square of the turn count. The battery and inverter system, by virtue of having a known voltage and current at a fixed power level (seen most obviously on the DC side), effectively has an characteristic impedance of its own. Advanced players are encouraged to investigate the 'per-unit' system of normalising powers and impedances to system voltage levels.

The system designer has the role of judiciously matching the motor and battery to ensure that maximum power is still available at the highest design speed, whilst not going unnecessarily further past this point into still faster winds so as to minimise the loss in the conversion system (FETs + phase wires). Note that this also implies running bus voltages as high as you can *within the constraints of the chosen controller/FETs*.

John, it's not so hard to explain why a low turn winding has higher copper losses as a high turn count winding - even if the copper fill in the teeth is the same.
look, lets say you have a 1-turn motor: here there are assumed 70% of the total length of the winding located in the teeth, and 30% of the winding is located outside the teeth used for interconnections between them.
now compare it with a 10-trun motor: here you have lets say 95% of the total winding length in the teeth, and only 5% of the entire length is used for the interconnections.

thats the reason why the lower the turn count, the higher the losses even if the copper fill is the same, so jmz is absolutely right!

GUYS, if you comparing setup A with 100V and 50A, and setup B with 50V and 100A for instance, the low volt system would need 4-times larger wires for keeping losses similar, and NOT only 2-times like often believed. Also the controller needs to have 4-times lower resistance since P loss = I² x R
HERE is the Problem. We don't have such controllers and who wants to have and work with heavy, hardly solderable wires like a garden house on a high power e-bike?

 

[dogman dan]

For the mundo owner, yes, the 35 mm motors mentioned a few posts back would also work better than a mac for a heavy cargo bike.

Lots of motor choices, and I'm out of date on what's in favor lately. My main point is get a bigger motor than one rated for 500w. Something in a direct drive, wider than 28 mm magnets.

But really for the win using a hub motor on a cargo bike, dump the mundo for a cargo bike with a 20" rear wheel. Get an edgerunner. But that will cost a lot, so though not stellar in efficiency, feeding a larger hubmotor plenty of power will do er.

 

[Chalo]

[...]who wants to have and work with heavy, hardly solderable wires like a garden house on a high power e-bike?

John in CR!

I mean, your ride isn't cool until the cable harness weighs more than the bike frame, right?

Where'd I put my hydraulic crimper and $15 cable lugs?

 

[madin88]

low turn count means:

- a bit higher copper losses in the winding
- higher losses everywhere outside the motor, because nobody will run wires which are 4-times bigger when using only half the voltage and twice the current for instance
- same with the controller losses: nobody will use a controller with 4-times lower resistance when using only twice the current

another thing is charging: imagine a 1800W 36V charger for instance. it would need HUGE wires and connectors compared to a 72V charger.