Seeking motor and controller advice on 1-1.5kw folding bike build

[JesseW]

Hi all,

I'm new to the forum. I've spent a fair bit of time poking around the forum and the web and I'm going to throw out a request for some advice as I'm finding it a bit challenging to compare all the bits of data.

I have a camp supersonic folding bike I'm planning to convert to ebike.

https://campbikeusa.com/collections/camp-supersonic

My goal is to have a light weight compact bike that cruises at 25 mph, power to 30 might be nice but the bike isn't really going to be safe at those speeds to 25 max would be OK.

I currently have a 2016/17 Rad mini which I like but I'm trying to make something lighter, more compact and with standard narrow wheels that will go on a public bus rack. Bike will be used for commuting and generally getting around without a car.

Rear drop outs appear to be ~137mm.
I'm planning to mount batteries on the rack.
Tentatively planning to house the controller between the rack and frame in an enclosure.
Want to have PAS, throttle, and cruise.
Planning to upsize the front chainring to be able to pedal effectively at up to at lease 22mph
Planning to upsize the tires as much as the rims/frame will allow, frame looks like it would fit ~2" tires.
I plan to use torque arms and secure them somehow to the bike frame.
Planning to build my own batteries from 18650 cells possibly a big one for long range and a small one for lighter weight running around town. 48 or 52v.

So my main questions are:

I think I want to go the geared rear hub motor route for lighter weight. I'm leaning towards a MAC motor although I'm not sure this is best with the high RPM needs of a 20" application. It looks like the rear disc brake has the required 15mm clearance to work with the MAC hub. Is this a good idea or does anyone have a better recommendation based on my goals?

Controller is what I'm really wondering about, I understand basics of hall sensors and brushless motor controllers but would appreciate any input on best controller for this. I'd like the option to run at 48 or 52 volts. Ideas?

I don't totally understand display and cruise options. My frame of reference is my Rad mini. I don't need a fancy display but a cruise control feature would be nice. What setups work good for commuting and city riding?

Any other challenges or pitfalls anyone sees with a project like this.

Thanks so much in advance for any help anyone can throw my way!

 

[dogman dan]

Mac, or similar 500w rated planetary geared motor is your choice. 10t a good wind, don't go too fast, like 7t wind.

48v, meaning a 13 cell groups in series, charges to 54.6v battery should get you 25 mph, in the small wheel. 14s for a bit more, like 3 mph more.


Sine wave controllers are the best, but your needs will be met by even a very cheap ebay 48v controller. 1000w is all you need, 20, 22 or 25 amps controller.


Several retailers provide a ready to ride kit with everything you ask for. E bike kit, Em3ev, etc. Closest to you, Grin in Vancouver.

 

[docw009]

I would consider the BBS02. Eliminates need to mount a large 25A controller somewhere on your bike. Luna has already done it, and there is a user video that shows the range and speed you can get out of a 14S-2P 30Q pack. You'll add 8.5 pounds in the center and while it's not 1000W, the gearing will get you to speeds unsafe for a folder.

You'll need something like 52T /11T to be able to contribute pedal effort at 22 mph. You might have to find a folder that supports a cassette or you'll end up with a DNP Epoch freewheel, not known for taking the force of a mid drive.

I've built two folders with Q100H motors in the rear, and 20A KT-controllers. They're not fast, but are light at 33-38 pounds. I also have a 20' fatbike folder that is probably very close to the original Radmini but only 36V. It's 50 pounds, Rides like tank.

 

[dogman dan]

Yeah, on a 20" wheel, its hard to gear for much more than 18 mph pedaling. But that's a crazy efficient speed to go at. My 20 " rear wheel trailer hauler bike was set up with the typical 14t rear freewheel on the motor, and had a 56 tooth front ring. 18 mph was about as fast as it pedaled, and 20 mph fast as it went. It had a low rpm motor, so yours would be faster if you use a 10 turn wind mac. You'd have your 22 mph.

 

[pullin-gs]

Yeah, on a 20" wheel, its hard to gear for much more than 18 mph pedaling. But that's a crazy efficient speed to go at. My 20 " rear wheel trailer hauler bike was set up with the typical 14t rear freewheel on the motor, and had a 56 tooth front ring. 18 mph was about as fast as it pedaled, and 20 mph fast as it went. It had a low rpm motor, so yours would be faster if you use a 10 turn wind mac. You'd have your 22 mph.

Here is the 20" wheel setup I use on my etrike.
I built the rear powered wheel....has an 8speed setup and is 135mm wide. I use 1.25" tire in back.
I kept my stock 3x8 speed gearing (52T large front ring, 11T smallest rear) which allows me to peddle 24 MPH....20 MPH at my comforable cruising cadence.
Trike weighs 37lbs without pack/motor/controller, motor/pack/wheel/controller weigh additional 15 lbs. I weigh 180 lbs.
It will go 22 mph on flat road on 500w Q128C (328RPM, 36V).
10S LiPo 8Ah battery....good for 15-miles 15-22 mph....building a 18650 17Ah pack to double range.
Controller is a cheap 1000w 36v 38amp (I stripped off heavy finned box to shrink size...does not even get warm at 15 amps on hills).
VERY STEALTHY! Hard to tell it is e-powered.
I'm going for a 35 mile ride now unassisted without battery.....the motor freewheels with very little drag.

edit: Just got back from my UNPOWERED ride on my 22 mile circuit. I averaged 14.0 mph. The same trike before epower conversion could average 15.0 MPH on this route.
Primary difference is "draggy" rear tire (lower presure, wider stance), hub motor drag (motor armature freewheels, but bearing drag from seals is pretty high), and added 8 lbs weight of motor/electronics/heavier-spoke&wheel.

 

[JesseW]

Thanks for the thoughts everybody. I ordered a G311 bafang geared 250watt 8T fast wind hub motor kit from Grin tech. Thanks for the tip there Dogman. I was overestimating my power needs based on my Rad mini, forgetting it's controller "governs" or "throttles" down the power approaching 20 mph.

Hoping to power it with 48v battery, ordered a silver fish style battery on Aliexpress, a 20 amp hour module from Shenzhen sky technologies, fingers crossed that works out. I went this route because the 17-16 Rad mini I have already has the "silver fish" style battery so I'll have 2 interchangeable batteries that work on both bikes if it all works out. If the Aliexpress battery doesn't work out I'll probably just build my own in a silver silver fish case.

Got a 11t small cog on the freewheel which I hope to pair with a 56t upgrade to lightpro front crank which will hopefully give me some pedaling power in the low 20mph range.

I'll post here or start a new thread with updates on my build and how things work out with the Aliexpress battery.

 

[JesseW]

Quick update. I've had the bike up and running for around 100 miles of riding. I got my aliexpress battery which seems to be reasonable well put together for the low price tag- I'll post a seperate thread on testing and teardown of that battery. I didn't verify the speed on my display but I did measure my wheel circumfrence pretty carefully and the display was telling me I was easily cruising at 25 mph in the flat and hitting 30 mph with sprint pedaling or a slight downhill. I want to make a few small improvements but generally I'm very happy with the setup.

My first major problem has come from running with my G10 bafang motor engaged at too high speeds and the high erpm has broken a magnet free from the rotor. I didn't do my math and heed the warnings Grin Tech puts in their product description. Fortunately it was easy to get the motor apart and Grin is sending me another rotor which should have the set up working great in a few days. Going forward I'll use the speed limiter feature to make sure the motor isn't engaged over ~28 mph and that should avoid the same problem with high erpm breaking magnets loose.

I've got a 56 tooth chainring on the camp and with the 11t cog on the cassette I can pedal at a comfortable pace at 25 mph and still push the bike with fast pedaling well into the 30 mph range. I'll work on photos, looks like I have to host photos for the forum and then link to them which I don't have time for now.

 

[Chopcat]

If you still have problems I can recommend the SAW20 that comes with the brompton kit that they do. I have only 30 miles on mine but it is very impressive. 25mph no problem apart from shaking everything else on the bike off....

Trevor

 

[JesseW]

Cool Trevor,

I'd be interested to hear how your experience is going forward. I wanted the lightest hub motor (G10 is 2.7 kg vs. 3.4 on the SAW20) and I wanted rear wheel motor which is why I went the route I did.

To update my project I've broken another magnet free under heavy use and Grin is now recommending I limit controller wattage to 700 and I'll be dropping my controller speed limit to 27 mph. I'll still be quite happy with the bike as long as I can cruise at or slightly above 25 mph in the flat but this has been bit of a frustrating learning curve as each motor rebuild takes quite a bit of time with unlacing all the spokes etc. I guess that's the price to pay for getting max performance out of a little light weight motor. I am really happy with how light the bike is though. If I take the battery off the bike is quite light and easy to handle folded or unfolded.