My initial thoughts:
1) You need to change the amps for the Q100, as 52 volts and 20amps isn’t going to work. For the simulation, I use 15 amps.
2) Realistically for us, the maximum current isn’t too important. It only provides power to get you going, and you are going to supply most of that yourself (I’m out of the saddle when I accelerate). I’m happy with a low current (12amp) controller, as it forces me to provide the initial acceleration torque myself, and won’t get too hot. Remember, your cruising speed is to the right of the inflection point, so you (as a strong rider on a road bike) should not be using maximum current very often.
3) You can move your “speed” line to the right to account for your 200+ watts. You want the distance between the black line and the red line to be 200+ watts (that is the difference between the load and the motor’s power). (Question 3)
4) With those graphs, your cruising speed is dangerously near the max current of the controller – meaning that your controller will get very hot and likely overheat (unless you have a good heat management plan). (in other words, the cruising speed is near the inflection point of the red line on the graph – you want to be well to the right of this)
The power output of your legs seems to be similar to mine. Keep in mind that your leg power for an endurance ride is about 50 watts less than a shorter faster ride – 200 watts is pretty strong for riding 2 hours a day.
The MAC and the Bafang are pretty similar motors as I recall – it’s a tossup between the two.
And thoughts after reading the thread:
(Q2) The larger size of the larger motors is going to allow you to handle more power (more current) and give you faster speeds. You can decide if that is worth the weight.
I do agree, that 25mph is a lot easier, lighter, and more reliable than 30mph. However, you are talking a 10-minute difference in a 25-mile commute.
Personally, I would use the Q100 for speeds up to 25mph (with you pedaling 200+ watts), or the Q128 for speeds of 30mph.
And for the endless big wheel debate: 700c and 26” wheels are roughly the same size. (compare a 622-25mm vs 2.125”x26”). A road bike and road tire is 300-350 watts more efficient than a mountain bike at 30mph. Thus, with a Q100, I use a slower speed winding on my mountain bike (26” wheel) and a higher speed winding on my “big wheel” road bike.
A mid drive would be easier to design, but isn’t going to be faster on a flat commute. Where they excel is being able to downshift and climb.
Reliability (Q5): my biggest wear item is going to be the battery and tires. Plan on charging at work. Ideally you would not charge above 80% and not deplete below 30%. Most people just charge to 100% and leave themselves minimum ~30% unused capacity. That gives you a little head room for occasional detours, headwinds, and the battery capacity degrading over time.
mystryda wrote:So here are my questions:
1. I'm concerned with efficiency because of size/weight/cost of batteries. Do I understand correctly that the Bafang CST wins hands down in terms of efficiency, or am I missing something in my analysis of the simulations?
2. The Bafang CST and MAC 8T both weigh double that of the Q100 CST. Is the efficiency worth the weight hit?
3. How can I interpret the graphs to tell what happens when I pedal? This one really has me stumped!!
--Me adding 200W to the 400W of the motor puts the speed at about 28 mph.
--If I look at the graph of the Bafang CST at 400W, for example, then 28 mph is extremely close to the no-load speed/0 amps expended, so that doesn't seem to make sense.
--Is there a way to accurately simulate what happens when I add 200W of pedal power?
4. Aside from the difference in cost and weight, why pick of these hubs over another? Or why not pick the Bafang CST?
5. I'm planning on pedaling up to the teens before engaging the motor, and I can treat the system gently (I just changed the original front brakes pads on the Odyssey at 106k.) However with commuting 12,000 miles annually reliability is a huge concern. Thoughts about reliability given these simulation results?