Hub drive torque limitations. Steep hills while towing a child?

After building several electric gokarts ranging from 350w to 13kw I'm now looking into building an ebike.

My fast kart weighs 200lbs, I can't ride any of my karts outside of my subdivision, and I'd like something that I can go out further and tow my daughter behind me.

I'm looking at rear hub motors instead of mid-drive due to simplicity and lower cost. I just want to verify that they have the torque for steep hills while lacking the advantage of multiple gear ratios. I'd also over-volt the motor so I can hit 45mph for when I'm riding solo.

Thank you

A 25 pound hub motor, meaning a massive and very power consuming motor .

Look at what Volton in Santa Barbara , California has done and
also
the member who lives in Costa Rica these days, I forgot his username it is something like ... CR in Paradise

For hills lower voltages and higher amperages .

For speed higher voltages .

So perhaps for you 2 different batteries , with a Cycle Analyst to adjust the low voltage cut off for the different batteries . This is what I do depending if I am riding mostly flat areas or hills on any ride. Sometimes take two batteries and adjust the LVC on the Cycle Analyst when switching battery packs.

Huh, I always thought watts were watts with the only difference being high voltage means less amps with less heat and resistance.

Bmr4life said:

Huh, I always thought watts were watts with the only difference being high voltage means less amps with less heat and resistance.

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Watts are watts. But different motors are different at better things; one motor (with a low Kv rating) might do great on hills but have a low top speed, while another (with a high kV rating) might not generate enough torque for hills without a disastrous amount of current through the windings.

Yes the same motor can be rewound to **either** deliver more torque / amps / heat at low speed (start from stop, steep hills and/or more weight),

**or** arrive at a higher top speed, which is a function of high voltage.

To get both rather than compromising, you need gearing.

And the former is very energy inefficient and stressful, so if you do have gearing use that to get your torque, and set your windings to deliver top energy efficiency at your usual flat-cruising speed.

Higher voltages, staying well below component ratings, are less stressful.

Top speeds are very inefficient wrt range

billvon said:

Bmr4life said:

Huh, I always thought watts were watts with the only difference being high voltage means less amps with less heat and resistance.

Click to expand...

Watts are watts. But different motors are different at better things; one motor (with a low Kv rating) might do great on hills but have a low top speed, while another (with a high kV rating) might not generate enough torque for hills without a disastrous amount of current through the windings.

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Correct, same logic with RC brushless motors. Look for the lowest KV motor that hits the top speed I want at a given voltage.

john61ct said:

Yes the same motor can be rewound to **either** deliver more torque / amps / heat at low speed (start from stop, steep hills and/or more weight),

**or** arrive at a higher top speed, which is a function of high voltage.

To get both rather than compromising, you need gearing.

And the former is very energy inefficient and stressful, so if you do have gearing use that to get your torque, and set your windings to deliver top energy efficiency at your usual flat-cruising speed.

Higher voltages, staying well below component ratings, are less stressful.

Top speeds are very inefficient wrt range

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So the moral of the story is I will have to pedal with a hub motor but will be a lot easier than without one.

? @scooterman101

why not just use the higher voltage battery and lower throttle to get the same motor operation you would get from a lower voltage battery?

i can't understand what you would get by actually swapping batteries simply to get a higher or lower voltage to get a higher or lower motor speed.

the controller converts the one to the other based on your throttle usage and whatever it's programming is so it is completely unnecessary.

Bmr4life said:

After building several electric gokarts ranging from 350w to 13kw I'm not looking into building an ebike.

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if not an ebike or a kart, then what specifically are you looking to build?

I'm looking at rear hub motors instead of mid-drive due to simplicity and lower cost. I just want to verify that they have the torque for steep hills while lacking the advantage of multiple gear ratios.

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that entirely depends on:
-- exactly which version of which hubmotor you use
-- diameter of wheel you use it in
-- voltage you run it at
-- current limit of the controller and it's design and programming / settings
-- capability of the battery to supply the current the controller needs without sagging in voltage too much to give the wheelspeed needed

etc.

i would strongly recommend you go to http://ebikes.ca/simulator , read the entire page so you know how it works and what each thing does and how to use it, and then play with different systems until you get an idea of what you would need to do what you want, without overheating the motor.

most of what they have are ebike motors, but the simulations and systems still apply to your problem and will show you at least how to determine what you need, even if what's listed there doesnt' do what you want.

I'd also over-volt the motor so I can hit 45mph for when I'm riding solo.

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if you use the right motor there is no "overvolting" needed. you just pick a motor that's actually capable of what you're after, speed and torque, and then use your throttle to determine what speed / torque you get out of it.

So the moral of the story is I will have to pedal with a hub motor but will be a lot easier than without one.

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nope.

just pick the right motor, controller, and battery, and it will do whatever you want it to.

If you haven't already done so, give this page a good read.

https://www.ebikes.ca/learn/power-ratings.html

I don't know how heavy your child is but ive flared out torque arms while pulling a trailer, 30lb load, if youre pulling hard up a hill with weight and then regen braking downhill if theres any give in the fit it wiil flare out at the axle. youll feel it when it happens. get good fitting torque arms and use 2 of them. hs3540 motor, 15s battery at 40 amps,70km/h with a 26 inch hookworm. easy pedalling up a steep hill doing 25km/h with trailer behind. thinking of switching to a 4t mxus v3 turbo with a 26 inch rear o.d. tire and a 17s battery at 35/40 amps and statorade.

Bmr4life said:

So the moral of the story is I will have to pedal with a hub motor but will be a lot easier than without one.

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Depends on your design. I have a 1500 watt hub motor and I rarely have to pedal up anything. I would also point out that there are two speed hub motors that give you a low and a high gear.

Bmr4life said:

I just want to verify that they have the torque for steep hills while lacking the advantage of multiple gear ratios.

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What do you consider a steep hill. I think above 15% as steep, but depending on where people live, 7% may be steep. If the latter, then I think a hub motor would be fine.

PS. Don't tow your daughter directly behind the bike; in some places it may be child abuse. Consider a trailer of some sort.

E-HP said:

Bmr4life said:

I just want to verify that they have the torque for steep hills while lacking the advantage of multiple gear ratios.

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What do you consider a steep hill. I think above 15% as steep, but depending on where people live, 7% may be steep. If the latter, then I think a hub motor would be fine.

PS. Don't tow your daughter directly behind the bike; in some places it may be child abuse. Consider a trailer of some sort.

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According to Google is looks like a 5-7% gradient in certain places.

I have one of these for the towing.

Bmr4life said:

According to Google is looks like a 5-7% gradient in certain places.

I have one of these for the towing.

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so assuming you have a couple hundred pounds of vehicle, then say 300lbs of rider and passenger (since you gave no numbers, we go on the heavy side for calculations), total 500lbs to pull up the hill, then the default crystalyte hs3540 motor in a 26" wheel with a 40a controller and 72v battery, no human power, full throttle, gets you 3 minutes of riding up the 7% slope at 20mph before the motor melts at 250 degrees C.

using instead a 20" wheel, you actually get a faster speed of 22mph, and over 5 minutes before overheating.

if it's only 400lbs total, then you get 8 minutes at 26mph.

slow down to 10mph and you get almost half an hour before overheat; meaning it'd have to be more than a 5 mile long uphill at that speed and slope to overheat the motor
https://www.ebikes.ca/tools/simulator.html?grade=7&hp=0&mass=181&autothrot=true&cont=C40&batt=B7223_AC&throt=34.8&axis=mph&wheel=20i


that same setup on the last one but going on the flats would reach 37mph with no overheating.
https://www.ebikes.ca/tools/simulator.html?grade=0&hp=0&mass=181&autothrot=false&cont=C40&batt=B7223_AC&throt=100&axis=mph&wheel=20i
so a bigger wheel would make it go faster but at the cost of more heating on the hill

so some other motor that can take more heat for longer, or options like statorade and hubsinks, etc, or bigger motros no tin the simulator, would help with that if you really need them.

seriously, just poke around in the simulator for a while and yo'ull see you can do what you want to do.

i can't simulate what you need because you don't give all the conditions / specs /etc to us that are needed to do it. so you have to do it yourself.

Thank you, that was very helpful. It's nice they have those kind of simulations for slopes.

amberwolf said:

slow down to 10mph and you get almost half an hour before overheat; meaning it'd have to be more than a 5 mile long uphill at that speed and slope to overheat the motor
https://www.ebikes.ca/tools/simulator.html?grade=7&hp=0&mass=181&autothrot=true&cont=C40&batt=B7223_AC&throt=34.8&axis=mph&wheel=20i

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AND, if you add 100W of human power, then it never overheats.
https://www.ebikes.ca/tools/simulator.html?grade=7&hp=100&mass=181&autothrot=true&cont=C40&batt=B7223_AC&throt=33.2&axis=mph&wheel=20i

From what I've read a mid drive is better for uphills.

But to share: I do have a 1500w rear hub and a kid trailer similar to yours. I had a PhaseRunner sine wave controller and it had NO power going up hills. Even hills that weren't that steep. That costed $300 bucks.

Then I recently bought a cheap 48V-72V 50A trapezoid/square wave controller just to try for $40 and it rips! Pulls harder and has faster acceleration than the $300 one.

But I'm not sure though if hauling kids around at fast speeds is a good idea. As long as its reasonable, you should be ok. And also invest in a good rear view mirror.

rockstar195 said:

Then I recently bought a cheap 48V-72V 50A trapezoid/square wave controller just to try for $40 and it rips! Pulls harder and has faster acceleration than the $300 one.

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I believe a trapazoidal controller is the most efficient commutation method for a BLDC/trapazoidal motor, since the drive current's wave form is a closer match with the wave form of the back EMF. It also will provide the most starting torque. Too bad they aren't silent.

What is human power :lol:
What are chains :wink:
Shifters whaaaat

Kidding aside, any bit of extra pedaling helps a lot. Right now, I weigh in at 375lbs, on a 9C clone front hub, and I am on one gear only f & r 42T front and 18-20T rear which is bad for climbing hills but I can notice a huge difference in some circumstances when it comes to slight hills, or any hill that slows me down to a slow speed, and even a little bit of extra pedaling, however little pedal power put into the effort, helps out tremendously.

E-HP said:

AND, if you add 100W of human power, then it never overheats.

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So much misinformation in this thread. I thought we had gotten past the notion of 'torque' or 'speed' windings.

Differing windings are capable of exactly the same amount of torque per unit of heat generated, they just take different combinations of voltage & current to supply the wattage required.

danielrlee said:

So much misinformation in this thread. I thought we had gotten past the notion of 'torque' or 'speed' windings.

Differing windings are capable of exactly the same amount of torque per unit of heat generated, they just take different combinations of voltage & current to supply the wattage required.

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Everything else being equal (i.e. for a given controller and battery, and their peak voltage and current limitations), different motor winds DO produce different peak speeds and torques.

So in reality, there ARE torque and speed windings, and it is not misinformation.

serious_sam said:

.....So in reality, there ARE torque and speed windings, and it is not misinformation.

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That's just incorrect. As individual components, there's nothing to make them 'torque' or 'speed' windings. What you are doing is giving a specific context of a complete system with predefined parameters. It is the combination of all these parameters together that dictates the performance of the system, not the motors themselves.

I'm personally happy to refer to them as 'fast' and 'slow' windings, but not 'speed' and 'torque', as it is all too easy to take the labels out of context, as you have demonstrated.

danielrlee said:

What you are doing is giving a specific context of a complete system with predefined parameters. It is the combination of all these parameters together that dictates the performance of the system, not the motors themselves.

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Correct. That's exactly what I did. Provided a specific context (common controller/battery limit), in order to directly compare the different motor windings.

danielrlee said:

I'm personally happy to refer to them as 'fast' and 'slow' windings, but not 'speed' and 'torque', as it is all too easy to take the labels out of context, as you have demonstrated.

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If anything, I highlighted the fact that I was comparing the different winds in a specific context. I did not take anything out of context.

The fact is, that in the context I provided, one wind will provide higher peak speed (and lower torque), and one will provide higher peak torque (and lower speed).

https://www.ebikes.ca/tools/simulat...ust_150_250_0.03_T&cont_b=cust_150_250_0.03_T

danielrlee said:

That's just incorrect.

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No. Nothing I have said is incorrect. You may not be happy with my descriptions (torque/speed), but that doesn't make me incorrect.

Re windings,,, pick the winding that suits the speed you plan on riding. So 45 mph,, that's not the low rpm motor.

There are different rpm windings for sure, that is a fact. Its a myth that the low rpm winding has more torque. Both winds will have same, or nearly the same torque at 0 rpm and max watts supplied. They will react very differently to being overloaded though, and this often is felt by the rider as a different torque. Its not, its just a difference in what rpm the motor runs overloaded. Both motors overload to the same rpm up the hill, but the slow motor is not so far into the heat making rpm at that speed, because its slower wound.


If going slow is your intent, because you greatly overload all the time, then the lower rpm motor will waste less energy at low rpm and overloaded than the faster wind. Not overloaded, both winds will run efficiently at low rpm. The difference is seen when you overload.

The easier solution to this is not overloading. Don't climb hills with a 500w rated motor and vehicle weights over 300 pounds. To weigh more, bigger motor able to handle more watts. Simple really. Gearing down helps as well, such as smaller wheel diameter.

Back to your specific needs, and its solution.

All you need for your plan, is a heavy direct drive hub motor of typical rpm winding. Meaning at 25 pounds bare motor, its got more copper, and bigger magnets than the typical 500w rated, 15 pound dd motor typical in the "1000w" kit. Now you are not overloaded towing the trailer, and have a motor able to handle huge wattage with ease.

45 mph will require more than 3000w, so this gets you into really big, heavy, hard to carry high voltage batteries. Really, for 45 mph or more, get a gas motorcycle or scooter. Its just sooo expensive to go fast electric compared to a cheap well used motorcycle. If you have the batts around, its simply sooo hard to carry much range, when you blow out 2000 watt hours in 30 min. But you can get a controller with a wide voltage range, and vary your battery voltage for fast or slow riding if you would like that. Its just that the fast ride is generally always too short, or you carry so much battery the bike handles poorly. But 10 mile range fast is easy to carry, if that is long enough for you.

A real nice 30-35 mph cruise speed, and towing your kid up steep hills at 15 mph is relatively cheap and easy. Again, the bigger motor, plus a 48v 40 amps controller. 2000w will pull 400-450 pounds total vehicle weight up the rocky mountains, and the big motor will merely get warm, not overheat.

A 52v 20 ah battery is big, but not too big to carry, and will get you a decent length ride, even at 30 mph cruise.

Great explanation

dogman dan said:

pick the winding that suits the speed you plan on riding.

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Also if the big limiting factor is the high torque required at low rpm, trying to avoid overloading in that context, and speed is not desired at all

then a low winding is better, because

> the slow motor is not so far into the heat making rpm at that speed, because its slower wound.

> If going slow is your intent, because you greatly overload all the time, then the lower rpm motor will waste less energy at low rpm and overloaded than the faster wind.

well put.

danielrlee said:

I thought we had gotten past the notion of 'torque' or 'speed' windings.

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So maybe **you** should stop putting out misinformation? Torque vs Speed windings is perfectly accurate terminology, given the right context.