Seeking advice for MAMIL ebike conversion

[ulrichw]

I've had to reluctantly admit to myself that the MAMIL description applies to me, and I'm looking to convert my commuter to a part-time ebike.

The bike is a cheapo Motobecane Mirage SL: http://www.bikesdirect.com/products/motobecane/road_bikes/mirage_sl.htm
I weigh about 160 lbs. (72.5 kg)
I'd like the motor to work for me on my mostly flat 10.5 mile (17km) commute with 30+ stop signs and/or traffic lights (I come to a near stop at all stop signs - don't unclip, but basically lose all my kinetic energy).
I ride fairly fast unassisted - flat/no wind around 22mph (35 km/h), with wind/drafting/slight downhill up to 27-28mph (43-45 km/h).
What I'm looking for is some assistance for easy days while keeping speeds similar (or maybe even slightly faster). On easy days I still expect to be contributing about 200-ish watts, so I don't need a very powerful motor.
I believe I want to ride primarily in PAS mode - I don't expect to be using a throttle much.
Because I have a Powertap (power measuring device - measures how much power I put into the pedals) rear wheel and would like to keep gearing for unassisted riding, I'd like to go for a front kit.
Because I'm lazy, I'd like to be able to ride unassisted efficiently without removing the wheel (I might remove the battery).

Having done some research, I'm tending towards something like a BMSbattery or Greenbikekit geared hub kit with an LCD display to control PAS level. I'm thinking I'd go for a 36v/350watts Q100 in a 328 rpm configuration (700c wheel). I'm thinking of going with a 10 Ah 36V bottle battery (with integrated controller). I intend to augment the kit with torque arms and possibly a brake sensor (though I may consider trying to scavenge the switches from the included brakes and rig something for my stock drop-bar brake levers).

Some questions:
- Any issues with my thinking? Anything I'm missing?
- How much control do the PAS levels give? I'm only looking for 100-200W of assist, but would like it to be available at the higher speeds.
- How much trouble will I have at slower speeds? (e.g., starting from stops, or my one 30-40 second hill where I'm going 12-ish mph unassisted) I do intend to be pedaling all the time and will probably be providing 300-ish watts on starts and climbs.4
- Is there any way to configure typical controllers to automatically avoid assisting at lower speeds? (I'm thinking to avoid overtaxing the motor at lower RPMs)
- Any other advice?

Thanks in advance for any help you can provide.

 

[d8veh]

The 328 rpm Q100 won't rub very efficiently in 700c wheels if you do a lot of stop and start. The controller will probably over-heat too because it will be running with the maximum current for a lot of the time. I would use a 260 rpm Q100H.

 

[ulrichw]

The 328 rpm Q100 won't rub very efficiently in 700c wheels if you do a lot of stop and start. The controller will probably over-heat too because it will be running with the maximum current for a lot of the time. I would use a 260 rpm Q100H.

Thanks!

Please check my math: Wouldn't a 260 rpm motor top out under 21 mph? I believe the rollout of a 700c wheel with a road tire is about 2.1 meters. So 260 rpm times 2.1 meters per revolution times 60 minutes per hour gives 32.76 km/h or 20.5 mph.

Am I misunderstanding something about the rpm rating? I took it to mean no-load rpm, I.e., the speed where the motor stops helping.

Is there a way to set a current limit on controllers to avoid the low speed issues? I am willing to do the work to get the bike moving, but I'd like help cruising at speeds faster than 20.5 mph

 

[Kepler]

Considering your are quite a fast rider without assist, I think the 328 RPM motor will suit your style of riding. Unfortunately the PAS function will work against you though as it kind of acts like an on off switch. This means you will go to the current limit of the controller on every start and basically stay on the current limit until you can get to speed close to motor's rated RPM. For running with PAS, the 260 RPM motor will be a better choice however you will lose assist above 32kph. Above this speed you now have a heavy arse bike that you need to do all the work with to go any faster.

If you want a high speed commuter that will give you assist up to 40kph, forget PAS and install a throttle so you have full control over how hard you are working the controller and motor.

Edit: Noticed the bike has drop bars so it doesn't suit a throttle arrangement. Personally I would then fit a throttle button that outputs a full throttle signal when pressed. Not a commercial item but quite easy to make with a simple voltage divider circuit.

 

[LockH]

I'm looking to convert my commuter to a part-time ebike.

Oh! First-time phrase for ES! A "part-time ebike"! hehe... Sorry. Couldn't resist.

Gotta be honest with you though. MY first experiences riding with an assist was an exercise in how to *avoid* using the batteries as much as possible. Crappy ol' lead-acid batts that were "dying" almost as soon as they were new. So, looking for any down hills. Avoiding head winds. (Stand up kick scoot w/extra "kick" via batteries and motor.) Aerodynamics like the "broad side of a barn door".) Kicking (think "pedaling") from starts and up hills. Etc.

Others here will have lots of good "techie" thoughts, but at least for higher speeds you might consider adding some sort of aero wind screen.

Cheers
L

 

[molybdenum]

chas58 Cute Q100 lightweight builds slow mtb, fast road build thread is a must-read for anyone interested in fast light-weight road bike builds with small motors https://endless-sphere.com/forums/viewtopic.php?f=3&t=49691&p=1187281&hilit=700c+26#p1187281


The 700c rim with a 30C tire is identical in circumference to a 26 inch rim with a 3.0 inch tire (Courtesy of Sunder). In most cases, a low power 328 RPM motor in a large wheel would be a big no-no; considering the OP is a fit cyclist who can steam up his sole hill at 20 kph, I think a 360RPM Q100 would be fine. The 260RPM @ 48V version would max out at 36-38 kph in a 700c wheel, which would be underwhelming to someone used to cruising at 40 kph on the flats unassisted.

The BMS battery Q100 motor can be purchased with the S06S controller and a compatible SLCD3 screen, and provides 5 handlebar accessible torque simulation PAS settings, which can be adjusted on the fly. A low PAS setting should reduce max amps sent to the controller without affecting potential top speed (unloaded speed). Starting on steep hills under power (high PAS setting should be avoided to prevent the motor from burning out. I would just turn the PAS off for this one hill until up to a safe speed of over 12-15 kph. Starting out at a low PAS setting or being easy on the throttle while starting will greatly extend the life of the motor and prevent stripping of gears or overheating.

 

[Kepler]

^^^

Good advice. Better option then my suggestion.

 

[ulrichw]

chas58 Cute Q100 lightweight builds slow mtb, fast road build thread is a must-read for anyone interested in fast light-weight road bike builds with small motors https://endless-sphere.com/forums/viewtopic.php?f=3&t=49691&p=1187281&hilit=700c+26#p1187281

The 700c rim with a 30C tire is identical in circumference to a 26 inch rim with a 3.0 inch tire (Courtesy of Sunder). In most cases, a low power 328 RPM motor in a large wheel would be a big no-no; considering the OP is a fit cyclist who can steam up his sole hill at 20 kph, I think a 360RPM Q100 would be fine. The 260RPM @ 48V version would max out at 36-38 kph in a 700c wheel, which would be underwhelming to someone used to cruising at 40 kph on the flats unassisted.

The BMS battery Q100 motor can be purchased with the S06S controller and a compatible SLCD3 screen, and provides 5 handlebar accessible torque simulation PAS settings, which can be adjusted on the fly. A low PAS setting should reduce max amps sent to the controller without affecting potential top speed (unloaded speed). Starting on steep hills under power (high PAS setting should be avoided to prevent the motor from burning out. I would just turn the PAS off for this one hill until up to a safe speed of over 12-15 kph. Starting out at a low PAS setting or being easy on the throttle while starting will greatly extend the life of the motor and prevent stripping of gears or overheating.

Thanks, Moly, for confirming some of my assumptions, and for adding some detail on the PAS function (also for the reference to chas' great thread, which I had already read as part of my research)

Thanks also to other posters in this thread - I'll probably pull the trigger within the next couple of weeks, and will post my results when I install the kit.