First Build, Seeking Advice

[RTFH]

Hey all,

To start, I'd like to announce to the world my first successful ebike! In actuality I've been riding it over a month (out of necessity - it's my only means of transportation) but until recently it's been like one long beta test, fixing bugs and redesigning on the go.

I commute ~15 miles each way to school over some seriously hilly terrain (SC County, high-five LFP!) so the goal was a heavy-duty commuter, a goal this bike meets and exceeds.

The frame is from a mongoose 200 XR, a cheap but solid mountain bike sold for a time at walmart. The battery is a 48v 20Ah high-C from BMSBattery rated for 60A continuous 100max, but I'm only drawing 30A through a cheap, generic Chinese 1500W controller en route to a magic pie front hub (the front-hub weight distribution is nice with a heavy load on the rear rack but can be frustrating climbing excessively steep hills or when rapid acceleration is required, and downright sketchy in wet conditions). This setup gets me to school and back with juice left over, throttling it all the way and cruising at 25-30 mph (with a fair amount of pedal-power on my part).

The battery/controller/motor system has worked like a charm since I hooked it up (after sorting through a nightmarish tangle of unlabeled and unsorted wires from my seemingly untraceable ebay mystery controller), but getting the "bike bits" (drive, train, shifters, brakes) working smoothly has taken some serious work. My life has been a good deal easier since I bought a pair of Avid disc brakes - a good lesson that saving money on parts can cost an exorbitant amount of time.

The super-low handlebar is to emulate drop-downs while retaining the control of a twist throttle. I used to commute on a cross bike which I loved dearly until it was stolen, and since then flat-bar setups just don't feel comfortable. I'm planning on mounting a second set of brakes on the drop bars so I can drop out of the wind for long flats or descents (and to look cool passing up other bikers 8) ).

All in all I am in love with the machine - I start and end each day ripping through town and woods, singing incoherently and grinning ear-to-ear - but of course it's still a work in progress. And so, dear denizens of Endless Sphere, I turn to you.

What I have is a cheap but solid frame, an excellent and under-utilized 48v 20Ah battery, a very cheap $1500W controller, a front 1000W DD motor (which I wouldn't mind replacing for a rear), and 50+Ah of used 18650 laptop cells I'm planning on building into a long-range pack (being careful not to draw over 1 C to avoid strain). I have adequate range and torque, what I'd really like is (of course) more speed. I have some saved funds, but I'd really like to minimize spending.

I know that air resistance becomes an increasingly pressing concern at high speeds, and I've been fantasizing about kitting out a sturdy recumbent with a wind-fairing, but I haven't been able to find any suitable recumbents on Clist for under $500, and even that I'm not sure I can justify given that I have a perfectly functional upright setup. Still, if anyone has any experience with high-power high-speed eRecumbents I'd love to hear about it!

My drop bars ought to shave off some drag for high-speed descents, but my front is still pretty rough. Do you all think a wind-fairing would be a worthwhile investment?

It seems that for high-speed bikes what I really want is high-voltage, but with $500 invested in a 48v battery I'd rather not jump ship. Plus, I'm really itching to push my pack past 60A...If I were to mod the shunt in my controller what could I expect in terms of speed? From what I've read I'm guessing I won't get much on flats, but given how much relatively slow hill-climbing I do the extra amps could be nice...alternately, would you recommend just buying a high-amp lyen controller?

And finally, how about if I switched out my magic pie for a rear high-speed winding setup? What models would you recommend to get me to 40mph on a 48v setup? (if that's a worthwhile goal)

Basically, how can I optimize for speed on a budget?

Thank you all!,
Russell

 

[wesnewell]

Modding the shut on your controller to 45A will get you a little more speed on the flats and a lot more on the hills. It will also get you faster acceleration.
If your commute was all flat, you could get a fast wind motor that would do 40mph on 48V, but with hills, I'd worry about burning it up.

 

[dogman dan]

No torque arm.

I agree, a super fast winding to get to 40mph on 48v is asking a lot on the hills, if you are sticking with 26" wheels.

40 mph for a daily street commute might get you noticed by the cops. I'd say go at this incrementally.

Start with a wide magnet motor. 5404, 3000w muxus, anything with at least a wider magnet than 28mm. I think your pie is even narrower than that.

3000w muxus motor on 2000-3000w is pretty perky, and the rear motor much better for control. Then once you are set up with a motor with more copper and wider magnets, you can decide if you really need to jump to 72v for the speed.

The main problem with 40 mph is you use double the power that 30 mph took. So now to go the same distance you need bigger, more expensive, and heavier batteries. So I say try a stronger motor on 48v with plenty of amps first.

 

[RTFH]

Thank you Wesnewell & Dogman!

For now I'll just mod the shunt to 45A as you suggest (and install a torque arm - in my defense its a solid steel fork, but I should've reinforced it long ago ), and I'll look into the motors you suggested DD.

 

[USAEBIKECO]

You must put a torque arm on that bike. You're really risking things not having one.

 

[RTFH]

Thank you for the reminder, I'll be switching things over to a new frame over spring break, that'll be priority number one.

 

[docnjoj]

Even 2 torque arms on the front. I've had motors spin in a few Walmart type rear suspension arms, also steel. I put 2 on my wife's delta trike steel fork front 9C motor and rest easy. She can easily spin the front wheel when she wants to. With 2 torque arms the motor stays where it is. If it spins out of the drops, very bad things happen. Also your MP has a good deal more torque than her 9C.
otherDoc

 

[RTFH]

Hi all,
After recurrent issues with the drive train I've decided to just get a new frame, and found one for $300 with high end dual suspension rock shox and plenty of frame room (http://sfbay.craigslist.org/scz/bik/4942278658.html). The forks are aluminum, so my front DD won't work, but I'm thinking this would be a good opportunity to make the switch to rear drive.

Does anyone have an experience with, or opinion about, this motor?
http://www.ebay.com/itm/2015-New-Style-48V-1500W-Brushless-Gearless-Cassette-Hub-Motor-for-Rear-Wheel/191442780832?_trksid=p2054897.c100204.m3164&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20140407115239%26meid%3De0685f864fad401fa2aca80a14ce7a67%26pid%3D100204%26rk%3D8%26rkt%3D30%26mehot%3Dlo%26sd%3D171560528671

Relevant specs:
Max. Speed: 600RPM
Max. Torque: 35N.M
Magnet Body Size: 13.65x3x35mm

Or else do you have any other suggestions for cheap ~35mm rear hub motors?

Thank you!