2WD motor efficiency

[gothicsurf]

The goal of this build is a bike that is efficient on the hills but also has a decent top speed. I am currently working with a minimal Bafang SWXK front motor which is just barely enough assist to make it back home fully loaded. The next step is to add a trailer weight of roughly 50lbs and for this will be adding a second motor.

The battery is also fairly minimal at 17Ah and 36V so would like to add as little weight as possible. I am hopeful that another minimal geared motor would be sufficient but also want to do better than just barely there. I have been considering a 500-1000W DD motor yet my climbing speeds may be in the 15mph range.

The compromise might be a more powerful geared motor. The elevation profile of my commute is attached showing the 1000ft climb one way. Regen would not be a major advantage because the downhill would be with a full charge.

 

[ZeroEm]

2WD motor efficiency
by gothicsurf » Jan 01 2023 1:10am

The goal of this build is a bike that is efficient on the hills but also has a decent top speed. I am currently working with a minimal Bafang SWXK front motor which is just barely enough assist to make it back home fully loaded. The next step is to add a trailer weight of roughly 50lbs and for this will be adding a second motor.

The battery is also fairly minimal at 17Ah and 36V so would like to add as little weight as possible. I am hopeful that another minimal geared motor would be sufficient but also want to do better than just barely there. I have been considering a 500-1000W DD motor yet my climbing speeds may be in the 15mph range.

The compromise might be a more powerful geared motor. The elevation profile of my commute is attached showing the 1000ft climb one way. Regen would not be a major advantage because the downhill would be with a full charge.

Sounds like you are riding something now with a Bafang SWXK, controller? and 17ah, 36v battery that is barely adequate. Guessing your not climbing hills at 15mph but want to. You are doing a lot of pedaling but want to do a little less. Now you want to pull a trailer and add a second motor.

I'm for 2WD or more than one motor. Not a way to keep weight down as you will need a bigger battery, another controller, with the weight of the second motor.
Will need more battery to increase distance and climb hills faster. Need a locked geared motor or DD to use regen.
10-15mph up hill is a good speed to shoot for. Small geared motors have a problem with heat on hills, something to think about.
Don't know what top speed your thinking of, might need to up the Voltage to 48v. Adding a rear motor can reduce your gears if you are running more than 7, depends on the motor. Pulling hills is never efficient, you just try not to over heat the motor.

Efficiency can be gained by keeping speed down <20, pedaling and regenerative braking helps with some recovery, best at extending the life of your brakes.

I ride a trike and with pedaling never need more than 1200w to pull 99% of the hills (no mountain's) around here >10mph. Me and the trike are 370lbs. So adding a rear 1000w motor with the Bafang maybe ok with more battery. When the Bafang burns out get a bigger geared front motor. Use the rear all the time and engage front motor on hills to help out.

 

[E-HP]

The goal of this build is a bike that is efficient on the hills but also has a decent top speed. I am currently working with a minimal Bafang SWXK front motor which is just barely enough assist to make it back home fully loaded. The next step is to add a trailer weight of roughly 50lbs and for this will be adding a second motor.

The battery is also fairly minimal at 17Ah and 36V so would like to add as little weight as possible. I am hopeful that another minimal geared motor would be sufficient but also want to do better than just barely there.

Use a trailer weight of 60 lbs for your design assumption, adding a second battery to the trailer that can be run in parallel with the existing one. That will give you both more capacity and more output current, to share between the two controllers. Use a larger rear geared hub in the 500W-750W range.

With that elevation change, regen is worth it though. You can always insert a toggle switch in line with the brake cutoff switches to disable regen when your battery is full. If you go that route, get the rear 1000W DD.

 

[motomech]

Been there, done that. OP, you might search my posts using key words, 2wd, motors, cute, Q100, etc.
The first and best thing you can start with is getting a 52 Volt pack. More capacity, more force, same space as your existing batt. You can use your controller and do a shunt mod., maybe up to 20 Amps max (50V X 20A = 1000 Watt.s, if the frt. was say 800 Watt.s, that would be 1800 Watt.s total).
As far as 2wd goes, I've used every combo of speed-ranges of Q-100' even mixed with Bafangs and an Ezee(DD's are way too heavy, especially if both are DD) and have found that two mid-speed range mini motors (like 260 rpm @36V) work the best. I used the rear all the time as the primary drive and added the frt. as needed. I always used two complete systems, 2 batt.s, two controllers, two motors, two throttles, there are a number of ways to do it, but i found that way was the simplist and obviously the most reliable (redundent even). Two mini's on 52 V Volts would get me up into the mid/high 20's mph, way fast for mini's (they seem to help each other along) and faster
than I really wanted to go. High speed range motors will gain a couple mph, but this doesn't work well overall, too sluggish in the mid speed range.
When climbing, I had to keep the Wattage on the frt. fairly low or the tire would spin because the rear driving force tends to unload the frt. tire a bit. When using the motors like I described. The frt. batt could be 1/3 rd the size of the main. That's what it always used. Actually, the frt. batt should be 1/3rd to 1/2 th the size of the main.
After many years I got tired of the added complexity, but really it was more my riding becoming more recreational (slower). For me, mid/low 20's is where I can pedal along with 11T/48T gearing, so that's the Sweet Spot.
If I were too build a more powerful ebike today, I would just use a single larger rear geared motor like a Mac.

 

[chuyskywalker]

If you haven't already, watch this a few times:

[youtube]Ub4EP2_mAds[/youtube]

And then go use the various simulator tools from Grin.