Finding a lighter motor with less drag

[keru]

Hi, I'm looking to change my motor.
I have a tridenttrike spike with 12s 8Ah LiPos and a golden motor magic pie 3.
I use it every day, It's fun but here are the small issues I have and trying to correct:
- the MP3 is heavy, an issue when I have to fold the bike and lift it (pretty much every day)
- the 20 inch wheel is really stiff, everytime I see a pothole I think I'm going to break another tire. Last time the tire got a hole. Also, I'm not sure having that much wheight in the back helps.
- the drag is intense, and I get the feeling that the motor is either too slow, making me having to 'push' the motor, or too fast, making me unable to pedal along.
I'm going to try at 24V trying to figure out if it's enough power for me, and I might go this way.

So I'm looking for an alternative/replacement for my MP3, with the following specs:
- lightweight
- able to pedal without the motor on, or actually pedal along
- I don't have much hills, maybe 2 times 5 minutes and one around 10-15 minute, but not that steep.
- not too expensive
- that would make me feel a bit more at ease regarding potholes

What got me to get the MP3 was the fact that it was easy to put in place, and that I could try and figure out what would be my prefered voltage. Also it did help push really well during the winter on slippery road and slush.

I'm hesitating between a mid-drive motor, maybe something I could mount near the bottom bracket, or a geared hub. I like the ease of installing a hub motor. Also someone pointed that even if there is an issue with the chain, a hub motor will be able to continue to push the bike. But (I'm not sure why) I feel a mid-drive is less complex than a hub, that would also put less weight on the back wheel, and might be a bit more efficient when comparing the weight. Also, if one day I change bike, the mid-drive might be easier to move than a hub, since the hub could imply to relace the wheel if it changes size.
Still, I feel geared hubs seem to fill my needs, but I'm not sure which one.

I saw the q100 or mxsus or mac or bafang ... and that got me lost ... the mac might be too expensive for me.

I'm wondering, if I get for example a 48v motor, could I still try to run it at 24v ? would I just need to change the controller ? Is there a controller that could be, like the magic pie, allowed to take from 24v to 48v ?

I also was thinking about trying to get something working with a 12v system and RC motors, but finding the right fit and making the reduction gear without tools got me lost too, maybe later ...

Thanks a lot and sorry for the long post.

 

[brumbrum]

A geared motor wiill let you free wheel with no real drag. A good option for price and weiight and reilability would be a Bafang BPM 500w. http://www.greenbikekit.com/electric-motor/rear-bldc-1/bldc-bpm-500w-36v.html


You can get different winding and voltages for differing power and rpm of motor.

 

[dogman dan]

If the hills are fairly mild, and your weight is not so heavy, a small gearmotor kit might be just the thing. For sure, about 9 pounds lighter for the smaller ones. Run it at about 800w max. I'm not sure though, if a single cross spoke will be possible. For sure, your current motor must have a radial lace. no spring in the wheel at all. But potholes will always be a problem with a 20" wheel.

I'm confused as to why you feel resistance while the motor is running. FWI, once you are traveling 20-25 mph, it will take a superhuman effort to add more speed from that. That's not the motor, it's the physics of wind drag. So a different motor will not change that much. What you can do easy though, is at 25 mph, pedal enough to lower the wattage your motor is drawing. That's not adding drag, so your 100-200w of effort may be doing you more good than you can feel. You will see it happen though, if you use a wattmeter.

If your motor is cogging crazy hard, like extreme hard to pedal it 3-5 mph, something is damaged, It may be shorting in the controller, wiring, or motor. Melty wires in the axle? Not real likely unless you run 72v though.

 

[keru]

Thanks for the replies, that's helpfull.
I can pedal the motor, not sure 3-5mph, I don't check the speed, but I have to be on the easiest speed. But I don't run it at 72V, the internal controller would fry before I even start I think.
I don't have a wattmeter yet, but soon, I'll check that.
The wheel doesn't have spokes, it is cast aluminum, I don't think it's leaving any flexibility like spokes. The rim too is pretty thick.
Also I'm wondering, regarding efficiency/range, would I be better using 24V 16Ah or 48V 8Ah ?

 

[dogman dan]

It should be possible to pedal to a certain rpm without feeling much resistance. But the same 5 mph in a 20" is turning the wheel faster. So I would expect you to feel something by 5 mph certainly feel it by 10 mph.

For sure, a cast wheel would be pretty rigid. But even a spoke wheel will be hard on tires, since ebikes tend to go fairly fast. But a single cross spoke should have at least some give compared to the cast wheel.

Re efficiency, that is not affected so much by the voltage. Speed is the key, faster is way more inefficient due to wind drag. Above 20 mph, range drops fast. Too slow can be bad too, if it's slow because a hill is too steep.

The best efficiency is fairly slow, but flat or gentle hills. 15-18 mph is where I ride to maximize range. This applies to fast or slow motors, at 36 or 100 volts. It's quite simple, slow is just less wind. Just like driving the car 55 instead of 75.

 

[d8veh]

The Bafang 500w BPM is a geared motor with a clutch. It's very strong, reliable and cheap, and it should be OK with your existing controller and battery.
http://www.bmsbattery.com/ebike-kits/585-bafang-350watts500watts-bpm-motor-e-bike-kit.html

Get a S12S controller, PAS sensor and LCD for better control of the power.