Internally geared BLDC motor

N

Norunec

100 µW
Joined
Nov 19, 2019
Messages
7
Hi folks,
I’ve been following this forum for a while, researching ideas to start a build of my own.
I’m really interested in super light motor setups just to help up the hills.
To that end, I recently stumbled across this interesting geared motor, and wanted to see what you all thought about it.

http://store-en.tmotor.com/mobile/goods.php?id=895

http://store-en.tmotor.com/bdimages/upload1/20190703/1562125630643055.jpg

I’m particularly inspired by the simpler, single reduction builds and friction drives as I’d want to keep the feel of my full suspension Whyte, but I would like a bit of assist going uphill as that’s what the local riding is like.

So, I was considering this motor driving the cranks via a freewheeling sprocket, so the drive is mostly disengaged on the downs, and a simple vesc with push button control.

Any thoughts gratefully received. And I know it’s quite expensive! But very lightweight...
 
One of the background images shows a really good looking double reduction with helical primary, but the exploded view of this drive is clearly just a single reduction of straight cut gears which is a pity. I'd love to know which of their products uses the double or if it's just stock imagry.

It claims peak torque of 18nm which if geared down 2.5:1 to the cranks for a 100rpm cadence would be a respectable 45nm. In theory since they designed this for robotics it shouldn't need a massive amount of cooling airflow. You may be able to overvolt it and run higher reduction with careful monitoring.
With a motor this small you likely don't need any freewheels except maybe on the crank and thats more for safety than anything else. If the motor drag is noticable then it can be mitigated with many controlers by running a small amount of current any time the front wheel is moving.

The question is whether they have overstated the continous and peak output like many RC motors do when used in a basically stationary application.
 
That’s what I thought, but at only about 550gm it ought to work well with a simple chain drive to the cranks. I guess you could run something close to a 3:1 reduction and push the voltage a little. That would potentially give you a decent peak torque, with an overall reduction of 27:1.
But, at more than 400$, I’d want to be pretty sure of it working....
 
I guess that’s roughly 10:1 reduction. My only thought was to aim for the motor benefits of a larger reduction without the normal additional weight penalties.
But that setup looks sweet.
Does it ride on the descents much as before the additions?
 
I've bought this for a similar purpose:
https://ru.aliexpress.com/item/32797544178.html

3 times heavier, but 3 times cheaper :)
Unlikely to fit your though.

Otherwise, this looks very good indeed, you can have something like 16T freewheel/36T chainring for a perfectly good cadence off 24v battery (depends on drop in loaded speed though) with a ton of torque provided you have low enough gearing in your transmission.
 
$400 for a 500w rated air cooled motor... OK, it's only 1lb, but that's asking quite a lot.

Personally i'd rather get a little dual reduction geared hub instead, for a third of the price.. i can stand another 5lbs!
 
I know, it’s hard to get out of the weight obsession sometimes. I could do with losing some off me first... :oops:
I did find this nice little helical reduction box
https://m.ru.aliexpress.com/item/32977118909.html?sellerAdminSeq=235664881&spm=a2g0n.search-amp.list.32977118909&aff_trace_key=aa481894cb264e2d8f91cdb85918e8bd-1573252551525-07822-bIArgx7K&aff_platform=msite&m_page_id=871amp-c8fnihg4XwhPwJ4Bnd_Hzg1573917141191
Which can take up to 6000rpm Input speed, but it’s quite long and there’s no weight specc’d
I thought it might go well with a pancake drone motor, which is why I was looking at that motor company where I found the geared motor. Which looked to be a really interesting product if a little (LOT) pricier as a route...
 
neptronix said:
$400 for a 500w rated air cooled motor... OK, it's only 1lb, but that's asking quite a lot.

Personally i'd rather get a little dual reduction geared hub instead, for a third of the price.. i can stand another 5lbs!
Click to expand...

It's interesting to note that the value metric on ES is $/watt , but those of us with cycling backgrounds its $ / gram saved. Depends on your priorities! I think that motor with 4 or 5:1 reduction at 36V would be pretty sick. The gearbox is a bit of an unknown, though. Hard to gauge the suitability for an ebike from those pictures.
 
My big concern is that it has an open case and will need to be sealed to live a long life in the elements.
And where's the dyno sheet?
Better be a damned good motorat that kind of price.
It would be sweet to have a 1lb motor and thus a 3lbs mid drive for sure..
 
neptronix said:
My big concern is that it has an open case and will need to be sealed to live a long life in the elements.
And where's the dyno sheet?
Click to expand...

Agreed. There isn't enough test data (maybe intentionally?). If they would post no-load current at 2 different voltages, we could use Justin's motor simulator to tell us whether it's worth pursuing . Who wants to buy one and post the results?
 
I’ve sent them some initial questions and have had a bit of back and forth, so I’ll post when I get some useful info.
 
I think you will be much better off buying a copter motor like one from drones:
https://www.dji.com/ru/e2000/info

(Peak efficiency of 90% at about 400 watts)

And than machining an axle adapter to that gearbox.
You should enclose it in some sort of shroud because case will be spinning, BUT it will have excellent heat dissipation properties, just make sure you have ventilation holes.
 
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