Low Speed, High Torque Hub Motor?

Daley

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Jun 8, 2021
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Hi guys.

I'm working on a project where I need a hub motor for very low speeds. The contraption should preferably use bicycle tires, for example 26". The speeds required are about 0-6 km/h. I have trouble finding a hub motor capable of accurately achieving these speeds. It also need sufficient torque to ensure a constant speed of the 70-80kg vehicle, regardless of incline or terrain (it will mostly be running on dirt). The motor can be either geared or direct drive, although direct is preferred. Does anyone know any motors that can do this job, or where I could go looking?

Speed: 0-6 km/h (0-3.7mph)
Suggested diameter: 26"
RPM: ca. 0-50 rpm
Vehicle weight: 70-80kg (154-176lbs)
Voltage: Any
Speed feedback: Yes


Thanks in advance for any and all help!
 
The problem without gearing is high amps at that low a voltage

you need controllers with heat sensors to stop before it melts

really big heavy ones will withstand the heat better

but look at gearing if you want to lighten the load.

Grin's simulator. . .
 
To be clear,.. it 'has' to be a in-wheel hub motor? Driving the wheel with an external motor and gearing could easily
achieve all those goals I would think. Just curious.
 
Any hub motor would struggle at those speeds if the load was very high, ie you are climbing a hill all day.

The magic pie and ASI hub motor would be the best choices here. They have the highest pole counts of any DD hub. Also using a smaller wheel ( 20" or less ) would increase the low end continuous torque capability.

This is also a very good application for a mid drive.
 
APL said:
To be clear,.. it 'has' to be a in-wheel hub motor? Driving the wheel with an external motor and gearing could easily
achieve all those goals I would think. Just curious.

Well, it doesn't have to be a hub motor, but it would be very advantageous for the structure and reliability of the vehicle. It is not meant to climb hills all day, it's only required to keep a steady speed across a field, with potentially a little incline. And the operation is only a few minutes at a time, with long brakes in between.
 
Daley said:
It is not meant to climb hills all day, it's only required to keep a steady speed across a field, with potentially a little incline. And the operation is only a few minutes at a time, with long brakes in between.

Well that is a completely different use case than your OP.

Literally any DD hub will do, so go for less weight.

Select one with a top speed just above what you need, not too high

at the voltage pack you decide on

in order to maximize the torque at the from-stop lowest speeds.

Again, get to know the Grin simulator.
 
DD is honestly not suited for this application. It will be needlessly heavy!

Just get a geared hubbie and call it a Day!
 
Daley said:
I'm working on a project where I need a hub motor for very low speeds. The contraption should preferably use bicycle tires, for example 26". The speeds required are about 0-6 km/h.

The low speed and high torque hub motor combination isn't a problem. But in a 26" bicycle wheel/tire is strange. As most of these applications used in a field use some sort of electric wheel barrow hub motor. So if the big bicycle wheel diameter isn't necessary then just use this: https://nl.aliexpress.com/item/3284...earchweb0_0,searchweb201602_,searchweb201603_



Wheel barrow hub motor wheel and tire.jpg
 
Vbruun said:
DD is honestly not suited for this application. It will be needlessly heavy!

Just get a geared hubbie and call it a Day!

Those will burn up even quicker in the wrong situation because they also perform poorly at super low RPM.

let the ebikes.ca motor simulator be your guide to this.
 
Hi, I have been looking around for similar specification but seems like with my required voltage and torque, I can't find anything suitable for me. any idea anyone?

My requirements are as follows:
Speed: 0-6 km/h (0-3.7mph)
Suggested diameter: 8-13"
Vehicle weight: 120-230kg
Voltage: 24V
Speed feedback: Encoder 1024ppr
Torque: up to 60Nm
Stall current: not more than 15A
 
Had a look on those motors, as I am looking for 24V, the output torque is not enough for my application
 
As you can't seem to be bothered explaining in more detail what you are building it is very hard to guess what is best for your application...
Probably a GMAC 12T motor in the smallest wheel/rim you can fit it into. But then you'd need a controller that will work with 24V and at high amps. Maybe a wheelchair worm-geared, brushed motor could work?
 
I have the controllers at 24V, the issue I have is that I am looking for a hub motor at 24V, high torque, and low speed. All these hub motors that are been used on scooters and bikes, all the 24V do not have high enough torque. I prefer it to be as one assembly too so this is a challenge too. I have been looking on brushless geared hub motors on Alibaba a lot but customer service are not the best to give accurate test curve of the motors etc.
 
Xrhstos_Cy said:
Hi, I have been looking around for similar specification but seems like with my required voltage and torque, I can't find anything suitable for me. any idea anyone?

My requirements are as follows:
Speed: 0-6 km/h (0-3.7mph)
Suggested diameter: 8-13"
Vehicle weight: 120-230kg
Voltage: 24V
Speed feedback: Encoder 1024ppr
Torque: up to 60Nm
Stall current: not more than 15A

Ali won't help with application requirements. You need to convert this to technical specs:
from torque to Kv:
Kt = 60Nm / 15A = 4Nm/A
Kv = 15/2π = 2.39rpm/V

from Kv to rpm:
2.39rpm/V * 24V = 57rpm

from rpm to diameter:
6km/h = 6,000,000mm/h
circumference = 6,000,000mm/h / 57rpm*60 = 1744mm
diameter = C/π = 1744mm / π = 555mm = 22in

As you can see, common direct drive hubmotors are not valid for these types of applications.
This Alibaba category will get you closest.
Otherwise, as was mentioned: an external motor and gearing which decouples motor speed from vehicle speed would be ideal.
 
Voltage is often easiest to adapt, so let's float voltage and fix wheel diameter to 13":

diameter 13" = 330mm
circumference = πD = π*330mm = 1037mm
rpm = 6,000,000mm/h / 1037mm*60 = 96rpm
96rpm / 2.39rpm/V = 40V

So a 48V system would bring these goals closer to reality
 
Thank you both for your replies!!

I started looking for 48V, to be honest. By calculations, it seems my application could work with the 48V. I tried to use 7.5A for each motor as this is the highest amps I will be using on each one and I reduced the speed to 1m/s which is around 3.5km/h as this is ideal for me too.

Now I will have to find a hub motor with 48V, but be able to have a rated torque around 5-7A.

I found this one: https://www.uumotor.com/15-inch-high-torque-slow-speed-gearless-hub-motor-with-encoder.html

They told me they can do multiple different sizes which are good, but I am not sure if supply it with a maximum of 7A, what is the maximum torque I will get out of it?
 
Go with a mid drive motor and figure out what battery, controller and gearing you want.

Check out the motor simulator
https://ebikes.ca/tools/simulator.html

BBSHD
https://ebikes.ca/tools/simulator.html?motor=MBBSHD&mid=true&gear=1&batt=B5220_GA&cont=C40&grade=20&hp=0&tr=36&tf=22&mass=170&throt=61&wheel=14i

Want more power to haul more weight?
https://www.cyclone-tw.com/product/1
 
Xrhstos_Cy said:
I started looking for 48V, to be honest. By calculations, it seems my application could work with the 48V. I tried to use 7.5A for each motor as this is the highest amps I will be using on each one and I reduced the speed to 1m/s which is around 3.5km/h as this is ideal for me too.

Now I will have to find a hub motor with 48V, but be able to have a rated torque around 5-7A.

I found this one: https://www.uumotor.com/15-inch-high-torque-slow-speed-gearless-hub-motor-with-encoder.html

They told me they can do multiple different sizes which are good, but I am not sure if supply it with a maximum of 7A, what is the maximum torque I will get out of it?


Very simply put: volts=speed, amps=torque
So why are you limiting yourself by only wanting to use a max. of 7.5A? More amps is more torque. The motor you linked to has a peak amp rating of 35A! It is the controller that feeds the brushless motor the amount of amps you program it to deliver (to it's designed maximum).
The way you are approaching it now is backwards. You shouldn't start with how many amps and volts you want to use.

So why not do it correctly and design your complete system in the best order?
1. Determine what you want to achieve (load, speed, wheel size, etc.);
2. Find a motor/wheel combo that can deliver that in your application (hills, weight, duration, etc.);
3. Find a matching controller;
4. Find a battery pack that can deliver the needed amps and has the capacity you need.
 
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