Hub motors at very low rpm - operating characteristics

Hi folks. I’m busily designing a motorized walker (the kind old folks use) - essentially, a very wide electric board with handrails. The key thing being that it will operate at very low speeds (4mph max). My 96-yo dad has been jonesing to add power to his walker, so I’m trying to oblige.

I’ve worked out a design using a standard belt drive, with a very high gear reduction ratio - but, for all the obvious reasons, I’d much rather build around a dual hub motor configuration. The thing is, that implies the motors turning at roughly 400rpm at 4mph (if I did the math right). The Maytech hub motors are rated at 60KV so, that implies that I’ll be running between maybe 1.5v - 8v and pretty high currents.

Does anybody have any experience/data/power curves for how these things run at low revs, with different rider weights? I’ve seen these things accelerate from a standing stop - so they can obviously generate the necessary torque - but what low speed operation implies for power consumption, and for optimal battery specs, is beyond me.

Any thoughts?



Glad to see this question come up because low speed control is something we don’t talk about much here.

Will you use VESC?

Re. VESC: Probably.

Though… I’m thinking very simple controls. Either on/off button for each motor, or a off/low/high toggle for each - with tank steering. It’s been suggested that a basic servo tester might be sufficient.

How good is his hearing? The vesc is more expensive but can be super quiet. And at those slowest speeds you’d definately want sensors added in the motor. I’d think you’d be more interested in these things than the motor efficiency at such low speed as you’ll use so little power it’s not worth thinking about. How would these work on the walker exactly? Might as well add a platform on it and just ride it maybe

Hearing is not great. Good point.

Re. how it would work, I’m looking at two options, both have platforms (the whole point is to ride!).

  1. Basically a platform with a dual-hub motor skateboard truck underneath, and a pair of casters, bolted to the walker frame. (An oddly shaped e-skateboard bolted to a walker frame.)

  2. uumotor makes some nice-looking hub-motor-tire combinations, designed for scooters - which could just replace the wheels on the walker. Still need a platform to stand on, but all it needs are some unpowered wheels.

By the way - I understand that you make hub motors - where can I find info on them?

I was trying to say if sound is important you can run the vesc in foc and quieter than all others.

I don’t have any motors now and will in the near feature but they’re way more powerful and over-built than what you’d need unless your dad wants to bomb up hills on his walker at 30mph. Is he that kinda guy? I’ll post stuff on my site in a couple weeks when they’re ready

I’m trying to imagine how you’d set it up: casters in the rear I imagine. Maybe that would work fine but I still wonder. It would be annoying to have to slow down and then redirect the walker towards a new direction all the time to turn. Does it have to be a walker? If only it could turn.

I’m thinking tank steering. Dual motors, selective application of power. Should work either with replacement front wheels, or with a dual-up truck at the rear of the platform.

Why are you running such low voltage? ? ?

Also…hub motors…if you run to low a voltage it will be like a car starting in 2nd or 3rd gear at start up…you don’t want this and will likely eventually burn out the motor pushing high currents through it

Perhaps I need to understand the motors better. I was under the impression that rpm is a function of applied voltage. Or am I missing something?

I dont think hub motors are what you are looking for. If you run a belt drive you can gear down so that you can get the desired speed without stressing the motor(s)

Dont be scared of belt drive its not that hard to maintain.

depending on the load your dad wants to put on the motor you may need either a controller that can put out a lot of amps or one that can put out a huge amount. But the motor should be able to perform as good as 12s I believe. When using a standard brushless esc the voltage the motor sees is an “effective voltage” much lower than the pack voltage. Hooking 50 volts directly to the motor would be a huuuuge current. Ohms law math would tell it.

Amps seem to be the only value in an inductor motor coil

It’s is…but…the higher voltage is like eating spinach for Popeye the sailor…so spinning at low speed takes very little amps…which is better for the motor …at the voltage you noted…the wheels wouldn’t even spin …

At the very least use a 6s system…I think those maytechs are rated for that also you’ll need a sensored motor setup to avoid the motor bog down or chatter starting from zero mph … it will make it a smother start

As long as there’s enough voltage to put amps into the motor determined by ohms law, which is very little voltage needed since the motor resistNce is very low, you can put many amps into a motor and get the same performance as with high voltage. Same heat produced. Same torque produced.

If u put a very high amp esc on the motor and set it’s limits high amps it will work. And ironically be slightly more efficient than with high voltage due to being run at a higher duty cycle while low speed

Yeah but it’s not a good idea … it’s on the verge of ridiculous to try …

Don’t do it …it’s stupid

Rethink your plan

theres nothing rediculous or stupid about it and as long as the esc can put out the amps it will perform just as well if not better.

if you used the vesc and low voltage you will likely hit an over-temp shut down from using so many amps and you will still have low torque as the vesc has programing that limits the motor amps to 120. (120 motor amps at 5% duty cycle or 5% of max speed when using 48 volt battery will only give you about 2.5 “effective volts” and add that up and youre at only 300 watts)

if you use the vesc and use high voltage it will work fine just be a bit inefficient but you will have the torque and power you want. if you use a 12v esc that can do 200 amps you will be the slightest bit more efficient and probably have even more torque than the vesc even with high voltage because of the 120 motor amp limit.

Have you ever seen a 12v car battery running a car starter-motor go-kart? they can be crazy powerful at low voltage if the amps are put in. there isn’t any extra heat and high voltage is cooler in power lines but not a motor

Re. motors being “overbuilt.” can you elaborate in two regards:

  1. Basic horsepower. I’m thinking that, at low speeds, with a walker frame attached, there’s going to be a good amount of mechanical drag - so the thing won’t coast a lot. That suggests that the motors will have to run for long periods, with all the wear and heat involved.

  2. Ability to run for long periods with no maintenance.

Any comments on these? Thanks!

if youre using castor wheels as the other two non-hub motors it wont be much drag.
unless youre doing steep hills or going very fast I doubt you’ll have any heat issues even if going for long periods. you wont be using much wattage on a walker likely.
hub motors have less maintenance needed.

you wont need anything “overbuilt” in terms of power or mechanically other than an overbuilt esc if you use low voltage

But I agree and he should get a low kv motor and higher voltage and the vesc. He will lose out on something any other way i think. get vesc on foc program at all costs It’s an interesting question bringing up kind of abstract understanding of how the esc and motors work and I think I have it right and hope someone who has a different understanding explains

@mfidelman1 are u saying ur going to drag the walker? I still don’t think it would be a problem to run it continuously with any hub motors out there and they won’t overheat. Unless he were to ride on the walker and it’s dragging. Don’t know what ur plan is really.

He’s not talking about 12v

He states 1.5v to 8v and based on that info I say shit idea