Freewheel for motor output?

Larby

1 mW
Joined
May 10, 2022
Messages
12
Morning all,

As part of my DIY mid-drive, I’d like to have a freewheel on the output shaft, so I don’t drag the system when pedalling unassisted.

Output shaft is a keyed 14mm (from a planetary gearbox)

I’ve seen people do this before, I’m figuring I’d need a LH freewheel on a LH thread, so it isn’t being undone by the drive force?

Trouble is, I can’t seem to find a LH freewheel in stock anywhere!

Am I missing something? Is there an easier way?

PS. I’m not talking about a crankset freewheel.

Cheers!
 
When I search online for "ACS Southpaw", I find them.
 
Chalo said:
When I search online for "ACS Southpaw", I find them.

Yep, but none are actually stocked and ACS don’t seem to be making any
 
Larby said:
Chalo said:
When I search online for "ACS Southpaw", I find them.

Yep, but none are actually stocked and ACS don’t seem to be making any

Maybe it's a UK thing. Four of the first six places I checked had it in stock.
 
Larby said:
PS. I’m not talking about a crankset freewheel.
FWIW, the crankset freewheels I am aware of use the same threading as the ones for the rear wheel, so if available with the correct threading version would serve the same purpose, as long as they support the sprocket size you wish to use (since they probably will not have teeth on them, but rather a bolt-on-flange with a BCD to match some chainring / sprocket BCD).


Regarding sources, this page
https://www.google.com/search?q=left-hand+freewheel
finds a number of places with info on them, and a few in-stock sources of different types. Whether any of them will ship to your location, I don't know--that you'd need to check. I also don't know that they are the specific thread pitch or diameter that you want (since that's not specified in your posts, but since your shaft is a fairly small diameter you could probably use *any* of them, just need to buy or make the right threaded adapter for your shaft).

Some example in-stock source links from the search:
https://www.benscycle.com/acs-southpaw-freewheel---16t--gun-metal--for-left-hand-drive-single-speed-freewheel-acs-k2725-fw1245/p

https://tncscooters.com/index.php?route=product/product&product_id=391

https://www.amazon.com/ACS-Southpaw-Freewheel-Drive-Metal/dp/B00X057BPY

https://www.ebay.com/itm/263877848884

https://www.walmart.com/ip/ACS-Southpaw-Freewheel-Left-Hand-Drive-20t-3-32-Gun-Metal/51743785


If you're really desperate, you can make a lefthand *jackshaft* freehub out of a righthand version, but it wouldn't mount directly to the motor.
http://www.recumbents.com/mars/pages/proj/tetz/VFS/projtetzVFS02lefthanddrive.html


As an alternative, since you have an output shaft that needs an adapter to mount a threaded freewheel anyway, you could just use / make one with a lip on the outboard (left) side, and then a standard righthand threaded version would work fine, as it would just tighten up against the lip exactly like it would against a rear hub, etc. Atomic Zombie used to sell this one
FDAX34%20Trike%20Axle%20FreeWheel%20Adapter%20T[1].jpg
and Staton sells ones like this
https://www.staton-inc.com/store/index.php?p=product&id=876
3247[1].jpg
3247-3[1].jpg

Staton also has LH freewheels on this page of various types of freewheels
https://www.staton-inc.com/store/index.php?p=catalog&parent=106&pg=1
and they also make a lockring for RH threaded FWs to do the same thing as the lip described above
https://www.staton-inc.com/store/index.php?p=product&id=1305
4047[1].jpg

If you have a lathe you could turn this down to 1.375" and thread it to match whatever FW you want to use
Weldahub W 5/8" ID Round OD is 1.625"
https://www.staton-inc.com/store/index.php?p=product&id=2059
0414[1].jpg
 
Larby said:
As part of my DIY mid-drive, I’d like to have a freewheel on the output shaft, so I don’t drag the system when pedalling unassisted.
:
PS. I’m not talking about a crankset freewheel.

If I may ask, what is the reason to use freewheel on motor shaft rather than on the crankset ?
 
Amberwolf - thank you for such an informative and detailed reply!
Now you mention it, I can’t believe I didn’t think of using a stopper flange on the outside. Basically, use a normal RHD setup, but turn it around on the shaft.
So obvious in hindsight! :oops:

Afzal - a freewheel on the cranks is usually to allow the motor to assist without the pedals turning. Assisted coasting if you like.

Freewheel on the motor output is to allow you to pedal, without turning the motor.

Most OEM systems have both, in some arrangement or another.
 
Larby said:
Afzal - a freewheel on the cranks is usually to allow the motor to assist without the pedals turning. Assisted coasting if you like.

Freewheel on the motor output is to allow you to pedal, without turning the motor.

Most OEM systems have both, in some arrangement or another.

Thanks Larby for replying to my silly :oops: question
 
Larby said:
Amberwolf - thank you for such an informative and detailed reply!
Now you mention it, I can’t believe I didn’t think of using a stopper flange on the outside. Basically, use a normal RHD setup, but turn it around on the shaft.
So obvious in hindsight! :oops:

Afzal - a freewheel on the cranks is usually to allow the motor to assist without the pedals turning. Assisted coasting if you like.

Freewheel on the motor output is to allow you to pedal, without turning the motor.

Most OEM systems have both, in some arrangement or another.

This may be useless trivia, but it is fairly simple process to change the ratchet direction on an ACS Freewheel by spending a little bit of time with a Dremel type rotary tool and a long thin grinding rod. Of course, you will have to deal somehow with the ratchet forces wanting to unthread the freewheel from the mount when being driven. It will need some additional/auxiliary scheme to lock it into place.
 
Larby,

If you have motor output on the right side, you can use a RHD freewheel with RH threads. The normal torque path for these "rear" freewheels is sprocket to threaded Hub. Your torque path is reversed, since motor hub transmits torque to sprocket.

The right hand freewheel/sprocket is mounted with the removal side (removal adapter slots) closest to the motor. The RHT hub with the 14 mm hole is on the end of the shaft. If the RH sprocket on the inside gives poor chain alignment, you may get better alignment by going with a Left hand threaded hub closest to the motor and LH sprocket on the end of the shaft.

I have used the cheaper ACS RHT flanges and freewheels on the motor and they hold up. It is on the rear wheel hub where torque can be 8 to 20 times more than motor output. Maybe the expensive White Industry rear freewheel? My ACS rear hub with the QS 2000 motor is still running -- but one once failed. I do use the $130. WI Ultimate hub on the QS 3000 bike.

As referenced above these parts are available from Staton, Inc and usually the cheapest priced.
 
I did a custom mid drive and for the cranks I bought a used Shimano FFS (front freewheel system) off Ebay.

Had 2 chainrings, one for motor and one back to derailleur. I did have to remove the inner ring and replace it with a larger one. 2 reasons.. 1 bigger ring for better gear ratio to the motor, 2 the two rings were too close together to run both chains at the same time. But a little drilling and some spacers and I was good to go.

Now a days you can purchase front freewheel crank sets by themselves from a few places that sell motors and scooter parts.
 
EDIT: I meant to post this on my main build post, not on this one! Sorry!

Well, I thought it's about time I posted a reply to show how I'm getting on with this!

I had a bit of spare time today, so have started building up the motor side of things. It's come together really nicely!

I'm using a Turnigy 6374 3500W 140KV motor and a 20:1 NEMA 24 gearbox with a belt drive for easy ratio swaps and silent(ish) running.

Bottom Bracket is an e-rider torque sensed (73mm to allow for the 68mm BB & two layers of 3mm ally) which will be running to a Cycle Analyst.

Motor is controlled by an 80A Turnigy VESC, to which the CAV3 will give a throttle signal.

The system will have a freewheel on the gearbox output, so it can be pedalled without dragging the system, but no second freewheel on the crankset at this stage. Using the torque sensor input, I have no desire for it to be able to drive without me pedalling. It'll simply add to the force I put in.

Next up, I need my transluscent orange PETG filament to arrive, so I can start printing covers and the battery assembly. Everything else it already here for the battery, I just need to add finishing touches to the battery design too.

Looking forward to testing it, I've never built or owned an e-bike before!
 

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