Bafang 24v 200W motor info needed

[HypnoToad]

I recently picked up a 200w bafang motor.

Now, I was hoping it would have 6 holes for a disc rotor, but instead it has a thread each side of the hub.

Very odd, does this mean that there is no way of adding a disc to this hub? Is there some sort of screw on adaptor available? I really need to use a disc rotor as my frame has no mounts for rim brakes on the rear.

Here are some photo's, apologies for the poor quality of them:

Motor:

Label:

Drive side:

Non-drive side:

Last but not least, how well would this motor handle 44v?

 

[amberwolf]

e-bikekit.com used to have rotors with threaded adapters built-in. Sickbikeparts.com probably still does, and pretty sure choppersus.com does. Might also have adapters t use regular rotors, too.

If you have a "chinese spacing" rotor already, I have an adapter ring cut from one that you can have for the cost of postage. It wont' fit a regular ISO spacing rotor, though.

 

[HypnoToad]

Thanks for the offer, I didn't know adaptors existed until I saw your post. I managed to find a shop that sells an adaptor and it should arrive in a few days with any luck. It turns out that this is what is known as a flip-flop hub, and now that I know I can get a disc on there then I've decided to use this motor as opposed to selling it.

Once more question about building it up to a wheel, it seems that the holes for the spokes are pretty large in diameter, the tip of this connector is almost 3mm wide:

Now, it seems that normal spokes are 14g which is 2mm wide and I have found someone the sells Sapim Strong spokes which are 13g at the hub, which is 2.34mm diameter as 12g seems to be too wide for the eyelets rim that I plan to use.

Will this be big enough and will using washers better the spoke head and hub holes be a good idea?

I've never built a hub motor into a wheel before now and I'd like to get it right the first time.

 

[amberwolf]

Look up JohnRobHolmes' custom spoke/wheel thread; there's lots of information in that thread even if you don't buy anything from it.

 

[HypnoToad]

Thanks, I've found the thread you're referring to, it's rather long but full of useful info.

It seems that Sapim make special spoke nipples that allow 13g spokes to be used in rim holes designed for 14g nipple holes, so I think I may go with plain 13 gauge spokes and see how it goes.

 

[HypnoToad]

Ok, I've got a 36h rim now and am calculating the spoke lengths, but while measuring the hub it turns out the width of the hub between the dropouts is 142mm, 7 mm too wide for my bike.

Now, is there a way of reducing the width somehow?

Can I do up this nut on the non drive side somehow in order to make this motor fit in 135mm dropouts?

Thanks

 

[Jeremy Harris]

I doubt thinning the nut down will help much, as you probably need that thickness to accommodate the freewheel depth and get the chainline something like right.

Could you just stretch the dropouts a bit? Usually they'll stretch out a few mm, unless there is a problem with something like the disc clearance further up. One way to gently stretch them out is to put a bit of 10mm threaded rod in the axle slots, with a couple of nuts and washers on the inside. Winding the nuts out will usually gently pull the fork apart a bit, often you need to stretch it out a fair way further than needed as it will spring back a bit when you undo the nuts.

Might be worth a try.



Failing that you could flog me the motor if it's a fast wind one!

 

[HypnoToad]

I doubt thinning the nut down will help much, as you probably need that thickness to accommodate the freewheel depth and get the chainline something like right.

The nut seems to be on the non-drive side of the hub, so if I did manage to get a thinner nut, maybe the disc caliper would be too close to the disc?

It seems the gap on the non-drive side is just over 7mm, so if I can get rid of this gap then this hub should fit 135mm or 136mm dropouts:

Here's another photo, I've added a direction arrow with some tape also:

Could you just stretch the dropouts a bit? Usually they'll stretch out a few mm, unless there is a problem with something like the disc clearance further up. One way to gently stretch them out is to put a bit of 10mm threaded rod in the axle slots, with a couple of nuts and washers on the inside. Winding the nuts out will usually gently pull the fork apart a bit, often you need to stretch it out a fair way further than needed as it will spring back a bit when you undo the nuts.

Might be worth a try.

I want to avoid stretching the dropouts really, as my frame is aluminium so if I can make the motor thinner then that would be preferable.

Failing that you could flog me the motor if it's a fast wind one!

It's not too late for me to return my rim. I have no idea about the specs or even the windings I'm afraid, I've seen a few sites selling a 250W model, so I guess internally this motor is similar or even the same? I know next to nothing about this motor, so what RPM at what voltage should I expect for the slow and fast winding version roughly?

Thanks.

 

[Jeremy Harris]

Do you know the width of the disc adapter?

A standard ISO disc has about 33 to 34mm diameter clearance in the centre, and if the disc mount adapter threads on the motor are the same as those for a freewheel (1.375" x 24) then the threaded bit will be around 35mm diameter, meaning that the disc may have to fit outside the thread, creating another clearance problem. Worth checking, as one option may be to machine down the thickness of the threaded boss on the non-drive side, to get the disc in a bit closer to the hub (if the calliper clearance allows for it), then fit a thin nut in place of the standard one that's there at the moment. Machining the threaded boss down to shorten it should be easy enough, and might not even mean taking the motor apart, just find someone with either a large lathe, or perhaps a small milling machine.

Have you tried just springing the forks out by hand to see if you can squeeze the motor in? You might not need to actually permanently spread them to gain just 7mm, so it might be worth a try.

Checking your photos again, the motor looks to be a 26" wheel wind for 24V (I think the "26" on the sticker is the intended wheel size), which would suggest it's probably around 200 rpm at 24V loaded (complete guess based on it probably being around 15mph top speed on 24V, which would seem reasonable for a low power motor). On 36 V the motor would probably run at around 300 rpm and on 48 V around 400 rpm.