Low/mid-power 20" folding bike build with 52v battery

[egosphere]

I have a Bafang middirve + 52v battery mountain bike build that I'm enjoying tremendously. Now, for my next project, I want to build a 20"-wheel folding rear-hub-motor e-bike for inner-city commuting. For my base bike I will probably use a Dahon Speed D7.

My question is what kind of hub motor and controller to get. I see there's a popular thread with the most powerful hub motors of 2016. But, I don't want anything too powerful -- this will be for 20~30mph stop-and-go city biking and I want to keep it light. The limitation is I want this to work with the battery I already have (52v) so I can just switch the batteries between the bikes. (I will likely keep the battery in my backpack while riding.) My (limited) understanding is that with higher voltage comes higher power and to keep up with higher power without melting you need a bigger motor (and also an appropriate controller). Hence my hesitation and my seeking help in your greater wisdom.

So what motor and controller combination would you recommend? I would ideally like to get a pre-laced 20" rear wheel kit so I don't have to lace it myself. But I live in NYC so I presume I could find a store that would lace a wheel for me if I have to get a bare motor. I am looking to be economical so Chinese resellers are ok by me.

Thank you.

 

[Drunkskunk]

The D7 is a good bike, but it's not a good bike for 30mph under power. It's a relatively flimsy frame designed to be light weight. Awesome for a folder, awesome for a pedal powered commuter. total crap for a high speed reliable commuter. Keep it at pedal speeds up to 20mph, and a Q100H would be a good motor for that bike.

If you need faster, pick a non folder 20" like what Spinningmagnets just posted, the Yoonqu. https://endless-sphere.com/forums/viewtopic.php?f=3&t=81277
A MAC motor on that would probably work with your battery to make an indestructible city commuter. it's doesn't fold, but it's small.

 

[egosphere]

Hi! Thanks for your response!

I'm not dead set on the D7 (not yet purchased). But I am dead set on a small folding bike. Would greatly appreciate alternative recommendations if you think the D7 is too flimsy! Or, let me know if you think no small folding bike is up to the task.

If I do go with the Q100H, do I have to worry about overvolting with a 52v battery? It's only rated for 350W, right?

 

[amberwolf]

For more advice about small bikes and higher speeds, you might look up Cwah's various threads about it; he's been given a lot of advice on that sort of thing.

 

[d8veh]

I fitted one of the first Q100s in my Dahon Jetstream P8. I used the 24v 201 rpm version at 12S (48v), which made it fly. It would cruise at just over 20 mph, even up slight inclines, without pedalling. I weigh 100kg.

Cwah used the 36v 328 rpm one at 48v in a 700c" wheel. he's very light, so can get away with it; however, when I opened the motor, after some use, the gears were quite badly worn. I think the 36v 260 rpm one in a 20" wheel at 52v might be OK if you don't weigh too much. 48v would be better.

Tiny motors like that are OK as long as you keep them spinning fast.