Low Speed, High Torque Hub Motor?

[Hummina Shadeeba]

U need to rewind a motor for a very low kv to do this as best as possible. Other ways are going to be problematic and perform worse.

I’ll rewind it for u for 100$ including shipping back and vacuuming in winding epoxy.

 

[Xrhstos_Cy]

Thanks for your reply. and yes. It's programed to receive a maximum of 7.5A for each motor, due to the motor controller. I will have all you said in mind and hopefully i will find a solution soon, thanks again

 

[SlowCo]

I will have all you said in mind and hopefully i will find a solution soon, thanks again

Not if you keep approaching the design and component selection backwards...

 

[Hummina Shadeeba]

He could do all common components and voltage battery if he rewinds the motor. For sure that’s got to be the best way to get what he wants. Otherwise with the high kv the torque per amp will suck.

 

[fatty]

Not if you keep approaching the design and component selection backwards...

It's not at all backwards if he has existing design constraints.
He's obviously not designing from scratch...

 

[SlowCo]

He wants high torque but will use 7.5A max
And he links to a motor that will take a peak of 35A.
If that is the type of motor that can fulfill his needs, he'll have to get the matching controller and suitable battery pack to go with it.

 

[haulincolin]

I was recently looking for a low speed hub motor and found Ozo (in France I think) has a variety of low Kv DD motors. Might be useful....

https://ozo-electric.com/en/27-brushless-bldc-motors?p=3

 

[fatty]

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?

Assume 250rpm @ 48V:
Kv = 250rpm / 48V = 5.21rpm/v
Kt = 60/2π/Kv = 60/2π/5.21 = 1.83Nm/A
torque = 1.83Nm/A * 7.5A = 14Nm

speed @ 250r/m w/ 380mm (15in) diameter:
circumference = πD = π*380mm = 1193mm
250r/m * 1193mm/r = 298300mm/m = 0.2983km/m = 18km/h

Kv still too high / Kt still too low

 

[arnolde]

Hello everyone,

I am also looking for a low-speed, high-torque, brushless geared hub motor.
I found this one on Aliexpress: https://www.aliexpress.com/item/1005005170833102.html
The torque goes up to 100Nm, although the specs are a little inconsistant (mentioning 200Nm somewhere too, but without details/proof).
If it really does have a (planetary?) gear ratio of 1:27 or 1:29 then it might be just what I need.
But I hesitate to buy 2 of those now for almost 700€ incl. shipping to Europe without being absolutely sure.

My application: A robot (about 80cm wide) powered by a large 48V/400Ah battery pack, which shall pull a machine over sand (riding arena smoothing device). I already have a prototype using 48V geared "wheelbarrow motors" but the gear ratio is only 1:3.6 or so, so it does not have enough torque. My controller (dual FSESC 6.7) can cope with 70A per wheel but I'm pretty sure I shouldnt use more than 20A or so for more than a few seconds. Another problem my prototype has, is that the wheelbarrow wheels dig themselves into the sand, so I will replace them with "lawnmower tractor" type tyres, which will hopefully be better suited.

I could of course go with manually assembling an "electric tricycle" motor with a large chain/belt reduction, but that gets mechanically pretty challenging, and I'd highly prefer a hub motor, also it looks much better and won't get sand inside, etc.

[youtube]OOZSHKcPm6E[/youtube]
(The background noise is rain on the roof. The motors really are that quiet!)

 

[Hillhater]

Until you get those fatter tyres, you might try letting the air pressure down very low on those wheelbarrow wheels to increase their “footprint” and grip.

 

[SlowCo]

I am also looking for a low-speed, high-torque, brushless geared hub motor.

No you should be looking at "snow blower tracks" and a second hand electric wheelchair. That would work much better in loose sand then small tires. And an electric wheelchair has all the fine controls already on board. You only need to remote control the joystick inputs.

Put these: https://nl.aliexpress.com/item/1005001491176454.html
or these:https://nl.aliexpress.com/item/1005003241769209.html







On something like this:https://www.ebay.de/itm/334730384633

 

[arnolde]

@Slowco Thanks for this input, those tracks do look interesting. Unfortunately both aliexpress links are dead, but I'll see what I can find. Looks like expensive shipping though...
EDIT: Found them: https://nl.aliexpress.com/item/1005005047042136.html - not all that bad, one pair for 325€ incl. shipping...

Regarding electric wheelchairs, I thought about those at one time too, and for a street rover (delivery robot) type application I might actually use one, but for this sand-rover project I've ruled it out for a number of reasons. I'm very happy with the frame, battery, controller I have - now I just need good traction and upto 1000N of pulling force (I will measure what is really needed with a scale soon).

One disadvantage of the tracks (depending on their size, hard to see from the photo) is that when skid-steering, it will plough up the sand - but the rover's job is to smoothen the sand

 

[arnolde]

No you should be looking at "snow blower tracks" and a second hand electric wheelchair. That would work much better in loose sand then small tires. And an electric wheelchair has all the fine controls already on board. You only need to remote control the joystick inputs.

I've now tried somewhat wider tyres (limited by rim size) and with a rougher profile, they still spin in the sand when pulling a heavy weight. Without the "trailer" it drives fine even in sand (with a little ballast). It looks like I might try those tracks after all, but I'll need a whole new motor & reduction setup for that. Now that I've seen what a VESC can do, I'll never use anything else though. I'm thinking of a 1:6 geared BLDC motor for large tricycles (like this one: VEVOR 48V DC Elektrischer Bürstenmotor, 750 Watt Electric Brush Motor 3100RPM, Bürstenmotor mit Steuerung für Golfwagen und Mobilitätswagen, Elektroautos, bürstenloser Motors Antriebskettenrad 420-14T | VEVOR DE) and then reduce that another 1:6 or so by chain or toothed belt. I only need 2-3 m/s max speed, but lots of torque.

Do you have a set of those tracks? Any chance you might be selling them again someday? Half their 350€ price is shipping from china, I'd be more tempted to try them if I could source them somewhere in Europe...

 

[SlowCo]

I've now tried somewhat wider tyres (limited by rim size) and with a rougher profile, they still spin in the sand when pulling a heavy weight. Without the "trailer" it drives fine even in sand (with a little ballast). It looks like I might try those tracks after all, but I'll need a whole new motor & reduction setup for that.

I don't have tracks to sell, you'll need to source them yourself. And I would try and reuse the hub motors you already have. Remove the tires and fix the drivewheel for the tracks to them. Or even use the tires as well inside the tracks. The tracks could be made from second hand 21" front motocross tires. Put the hub motor you already have and a freewheeling wheel inside the motocross tire like this:

or this:

You get the idea. You just need more surface and grippy tracks provide that.

 

[sk8rboi]

Taking this thread off on a tangent... does anyone know if a geared hub motor (from a donor E-MTB) could be repurposed in a high-torque, low-speed, self-balancing robot project? This project will need custom motors at some stage, but for proof of concept I was hoping to re-lace two 350w geared-hub eBike motors into my 13" parallel-wheel chassis (being light-weight is very important).

I've read about 'freewheel' and regen motors, do all e-bikes use freewheel, and would the freewheel be useless in a motor that needs to rotate forwards/backwards quickly to remain balancing? Can the freewheel aspect be modified/butchered?

There's other obvious compromises using a through-axle e-bike motor in a single-sided pair, but that's lower on the list of concerns at the moment.

 

[E-HP]

Taking this thread off on a tangent... does anyone know if a geared hub motor (from a donor E-MTB) could be repurposed in a high-torque, low-speed, self-balancing robot project? This project will need custom motors at some stage, but for proof of concept I was hoping to re-lace two 350w geared-hub eBike motors into my 13" parallel-wheel chassis (being light-weight is very important).

I've read about 'freewheel' and regen motors, do all e-bikes use freewheel, and would the freewheel be useless in a motor that needs to rotate forwards/backwards quickly to remain balancing? Can the freewheel aspect be modified/butchered?

There's other obvious compromises using a through-axle e-bike motor in a single-sided pair, but that's lower on the list of concerns at the moment.

Most geared hub motors have a clutch and the motor can only drive the wheel in the forward direction. A direct drive motor can be driven in forward and reverse. The GMAC geared hub doesn’t use a clutch, so that’s the exception. Unfortunately direct drive motors are usually heavier than a small geared hub.

 

[amberwolf]

FWIW, if you had a thru-axle motor, it would be easy to build a single-ended axle that can support the weight, since the axle is not part of the motor.

But almost no hubmotors use thru-axles, and none of the geared hubs I know of do (at least two DD hubs do).


As E-HP notes, the internal clutch in the geared hubmotor will prevent you running it backwards, so it won't operate a self-balancing system (it will just flop over in the direction the clutch doesn't allow motor to oppose).

To use your existing motors, you can weld the clutch so it will allow the motor to operate in both directions. If you don't need much torque you may be able to jam the clutch (to keep the rollers from going back down the ramps and allowing freewheeling) or even epoxy them in place, but these wont' resist higher torque and it will slip under enough load.