Originally Posted by
andychrist
While it’s not especially heavy duty, I built up my ecumbent cargo bike “Blutus” from a [sparkle blue] RANS Stratus XP incorporating dual Bafang 500W hub drives. So it kinda exceeds the legal limit but as I’ve got the cutoff set to 16mph and only ride on the shoulders of public roads, doubt I’ll ever be hassled. Am currently putting together a red Stratus LE with a TSDZ2 OSF and 20” Bafang 500W front hub, “Redundo” (because that model supports wider tires as well as a front fairing) whose speed I’ll similarly restrict.
Even unloaded, when climbing some of the steeper hills around here on Blutus, the 860C displays will occasionally report over 700W each, if only for a fraction of a minute. Once though, while attacking a wall in Catskill, a loose XT60 caused the rear hub to fail, and the front’s display hovered over 800W for the couple minutes it took me to reach the summit and address the electrical connection. Not a big deal I guess, but worry that should I ever venture beyond a 25mi radius from home, might encounter hills both equally steep and considerably longer than encountered locally. In which case, dunno how long Blutus could sustain the output needed to maintain a cruising speed of 12mph. So my ultimate ecumbent build will likely entail 1500-2000W continuous power, through some combination of hub/mid drives, not sure yet which. Preference would be dual 750 or 1000W hubs, but
AFAIK front wheels of that power are only available fat, D’oh!
Your post is a prime example of explaining how the regulations are actually written. The regulations are written as 750 watts motor output.. What you are saying is that "I briefly pull over 700 watts from the battery". 700 watts pull from the battery is not motor output, its battery draw. Motor output has to do with how fast the motor is actually turning and how big is the load on the motor. If you are at 16 mph and pulling 700 battery watts on each motor you were probably more like 300 watts motor output and 400 watts of heat being produced. Once the bike tops out in motor rpm, the load would drop and the amperage would go down and you would settle in around the 70-80% motor efficiency range. That being 70-80% of the battery watts are being used to drive the bike and 30-20% are dissipated as heat.
What I am saying is that the regulations were written to allow lots of battery watts draw for torque at low speeds where the total motor output cannot exceed 750 watts. to exceed the actual 750 watts motor output the bike usually has to be north of 25 mph on the level. Essentially, the regulations govern the top sustainable speed, not the low end torque for climbing. If the bike tops out with gearing at 28 mph, its hard to bust the regs.
My bike with full batteries can deliver a battery draw approaching 1700 watts. 750 watts motor output will be reached about the time the bike hits 24 mph. At that point the motor exceeds the 750watts output. The bike will reach about 28.5 mph at which point the battery draw goes way down as the bike reaches its max speed possible with the stock BBSHD controller. I could exceed this quite a bit by setting the display to kilometers vs mph and saying my wheel size is 18". the problem with that is that the BBSHD can overheat in 10 minutes or so even at 28 mph. I have plenty of battery to prevent serious sag at 28 mph but is had better be pretty cold weather for biking to actually sustain 28mph for very long.
So I can pull 1,700 watts from the battery but what can I actually sustain? I can actually sustain about 23-24 mph for 60 miles or so. The motor will get very hot to the touch but not overheat. I can only sustain this because I have a very huge battery bank. With a single 720 watt hour battery I am going to be hitting the voltage sag limits at about 16-18 miles.
The point is, although I technically have this "Illegal" bike, it is a bicycle and is pretty much self governing below the legal limit. That is with me trying to push the limits upward and go faster for longer periods. I can easily be stupid and exceed the legal limits but not for long. The motor will overheat or I will break something. Even stupid is self governing. .
So andychrist, I would not worry to much about your dual motor bike. You still will not be able to actually sustain an illegal output for more than a few seconds to a few minutes. The guys whom thought up the regulations actually knew how to write-in the cutoff between an e bike and a motorcycle without unduly burdening themselves on their own fun factor. Real pragmatic pros, not politicians.
Look for bikes in the future to really be able to spike the torque at low speeds with high battery draw (1000 watts+) for climbing and still be under the 250 watt motor output limits for Europe. 250 watts limits the bikes top speeds to around 18-20 mph on the level but does not actually limit battery watts draw. . 750 watts limits the top speeds to around 25-28 mph.
Still the most likely candidate to be going to fast on a bike path is a well heeled commuter with a brief case, not a teenager. Teenagers still ride Walmart push scooters, skate boards and bmx bikes for the most part. They are still a hazard on those.