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Deleted member 4366
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I know lots of people are interested in the BPM kit, so I thought I'd do another review and show a couple of solutions to problems. The kit is very cheap - about £200 delivered to your door from BMSbattery in China. The kit comprises 350w motor (code 12) in wheel, 350w 9 FET controller, throttle, pedal sensor and brakes with switches. The quality of the motor is fantastic, but be prepared to tighten all the spokes, as mine were too loose. the rest of the stuff is standard Chinese with the odd wire in the wrong position in the connectors, so check that they all match before assembling.
I've used the optional 30 amp 12 FET controller that has useful features like cruise control, speed limit and 3 speed switch and cost about £20 extra.
Assembling was very straight forward. The wheel fits straight in, but you need to make some anti-rotation arms to resist the huge torque from this motor if you don't want to shred your drop-outs. You get the usual p[problem of trying to find room to fit the throttle. I changed to a thumb changer to make more room, but my friend Steve (Saneagle) managed to fit his on a Marin without changing anything. The overall finished weight with battery is 23KG.
I have a front hydraulic brake so the supplied brake levers were unsuitable. Instead, I fitted a reed switch in the grip and mounted a magnet in the lever, which works perfectly. The switch is necessary because I wanted to fit a cruise control.
As I still have a cable brake on the rear (but not for long), I used the supplied switched rear brake lever.
Batteries are 44v 10aH lipos, which I've been using for several months and are necessary to supply the huge current. With lipos, it's necessary to monitor the voltage, so I fitted a watt-meter with the shunts removed and located at the battery.
A 20aH Lifepo4s would be OK but heavy and expensive. On my last build with this motor, I can easily do my 30 mile commute on the one battery with pedalling.
On first testing, the motor was drawing 40 amps, which is about 1.5KW - miles more power than anybody would want. On our 1 in 4 test hill, it accelerates all the way up from a standstill. No hill will defeat this set-up.
The motor is very quiet and smooth, and now that it's done about 1000miles, it's extremely free-running. Steve and I were racing a guy on a road bike down a long steep hill and I hit 39mph, while Steve with the same motor had to use his brakes to stop running in the back of me. The guy on the road bike said he hit 41mph, so you can say that there is minimal drag from these motors when run-in. Indeed, I regularly pedal it without assistance for exercise and to save battery and it rides just like a normal bike, but a bit heavier - no different to having a bit of shopping in your panniers.
I haven't done any speed trials with the new set-up because I have the speed limit connector engaged, which limits powered speed to about 18mph. The power is still too much. With the pedal sensor, the power comes after about 1 turn and then you can't pedal fast enough to keep up with the acceleration, so I've had to make a cruise control to limit it. I fitted a 10k potentiometer to the Left handlebar with a switch to switch from normal throttle to pot throttle. The pot throttle can be set to any speed, which means that you can have a nice leisurely ride, but with all the power you need to get up hills. This controller also has electronic cruise control, but you set it by keeping the speed constant for a few secs, but our roads are too bumpy. The pot throttle should help to set it.
The standard controller (not the one I have)only gave out 14amps until we soldered about 1/3 of the shunt to get it up to 25amps, which is a nice balance between control and power.Before the mod, it wasn't enough to get up steep hills without puffing.
Overall, I would say that if it's power you want, this set-up has it in spades, but at the expense of range, unless you can find some way of taming it like I did. With the standard controller and a 15aH lipo, it would be much more sensible, but you need 25amps to get up step hills.
Total project cost:
Kit £200 (new)
RockShox Dart 3 forks £70 (new)
Frame and rear shock £100 (used)
Crank-set £30 (used)
Rack and bag £8 (new)
Battery and connectors £130 (new)
Charger £14 (new)
Watt-meter £13 (new)
City Slick tyres pair £20 (new)
Other stuff £40
Total:about £620
You'd be lucky to get a second hand Giant normal bike for that, so that makes it a bargain in my reckoning.
I've used the optional 30 amp 12 FET controller that has useful features like cruise control, speed limit and 3 speed switch and cost about £20 extra.
Assembling was very straight forward. The wheel fits straight in, but you need to make some anti-rotation arms to resist the huge torque from this motor if you don't want to shred your drop-outs. You get the usual p[problem of trying to find room to fit the throttle. I changed to a thumb changer to make more room, but my friend Steve (Saneagle) managed to fit his on a Marin without changing anything. The overall finished weight with battery is 23KG.
I have a front hydraulic brake so the supplied brake levers were unsuitable. Instead, I fitted a reed switch in the grip and mounted a magnet in the lever, which works perfectly. The switch is necessary because I wanted to fit a cruise control.
As I still have a cable brake on the rear (but not for long), I used the supplied switched rear brake lever.
Batteries are 44v 10aH lipos, which I've been using for several months and are necessary to supply the huge current. With lipos, it's necessary to monitor the voltage, so I fitted a watt-meter with the shunts removed and located at the battery.
A 20aH Lifepo4s would be OK but heavy and expensive. On my last build with this motor, I can easily do my 30 mile commute on the one battery with pedalling.
On first testing, the motor was drawing 40 amps, which is about 1.5KW - miles more power than anybody would want. On our 1 in 4 test hill, it accelerates all the way up from a standstill. No hill will defeat this set-up.
The motor is very quiet and smooth, and now that it's done about 1000miles, it's extremely free-running. Steve and I were racing a guy on a road bike down a long steep hill and I hit 39mph, while Steve with the same motor had to use his brakes to stop running in the back of me. The guy on the road bike said he hit 41mph, so you can say that there is minimal drag from these motors when run-in. Indeed, I regularly pedal it without assistance for exercise and to save battery and it rides just like a normal bike, but a bit heavier - no different to having a bit of shopping in your panniers.
I haven't done any speed trials with the new set-up because I have the speed limit connector engaged, which limits powered speed to about 18mph. The power is still too much. With the pedal sensor, the power comes after about 1 turn and then you can't pedal fast enough to keep up with the acceleration, so I've had to make a cruise control to limit it. I fitted a 10k potentiometer to the Left handlebar with a switch to switch from normal throttle to pot throttle. The pot throttle can be set to any speed, which means that you can have a nice leisurely ride, but with all the power you need to get up hills. This controller also has electronic cruise control, but you set it by keeping the speed constant for a few secs, but our roads are too bumpy. The pot throttle should help to set it.
The standard controller (not the one I have)only gave out 14amps until we soldered about 1/3 of the shunt to get it up to 25amps, which is a nice balance between control and power.Before the mod, it wasn't enough to get up steep hills without puffing.
Overall, I would say that if it's power you want, this set-up has it in spades, but at the expense of range, unless you can find some way of taming it like I did. With the standard controller and a 15aH lipo, it would be much more sensible, but you need 25amps to get up step hills.
Total project cost:
Kit £200 (new)
RockShox Dart 3 forks £70 (new)
Frame and rear shock £100 (used)
Crank-set £30 (used)
Rack and bag £8 (new)
Battery and connectors £130 (new)
Charger £14 (new)
Watt-meter £13 (new)
City Slick tyres pair £20 (new)
Other stuff £40
Total:about £620
You'd be lucky to get a second hand Giant normal bike for that, so that makes it a bargain in my reckoning.
