Which motors for which wheel sizes?

[Arbol]

I was considering the purchase of an electric kit a few months ago, but I was scared about burglars (I live in Barcelona), so I continued without a motor.

The other day, a friend told me a way to hide efficiently the battery (it works for him): add a rear basket to the bike, and put a small battery below it (and the controller). Another possibility would be a folding bike, a 16'', ie either a Brompton or an Ori. I believe going to 20'' would be too cumbersome.

About the first possibility, I know what I would do: a q100h in 28'' wheel (I have a 7 speed freewheel), and a small 36V battery from Konions (there is a German selling those that can make strange geometries, such as a very flat battery). I would add a s06s or s06p, and try not to have any LCD or LED in order to get a stealthy bike.

About the second possibility, from what I read options are limited for Brompton: I do not like keyde because there is no throttle. A q85 fits (I have a friend who did exactly that), which is basically the only option. (but I saw in the past a MAC in the front of a Brompton, which I thought was surprising: is that possible, without affecting too much to the folding and drivability? I assume torque arms are essential).

My question refers to the Ori, eg the M9: apparently, the Ori has standard sizes (rear fork of 135mm and front fork of 100mm). As a consequence, one could think about adding a Bafang CST rear and run it with a 48V battery (either from the German, or a package of Samsungs from em3ev). I believe small wheels give better acceleration but lower speed. Since I want acceleration and I do not care much about speed, that would be an ideal solution, apparently.

But when I look at BMSbattery, GBK and others, wheel size for the Bafang 500W CST is only for big wheels, from 24'' to 28'':

http://www.bmsbattery.com/ebike-kits/589-q11-48v1kw-front-driving-hub-motor-e-bike-conversion-kit.html

BPM2 is for 20'' too:

http://www.bmsbattery.com/ebike-kits/586-bafang-350watts500watts-bpm-motor-e-bike-kit.html

And the q100h (an q100c) is for 16'' too:

http://www.bmsbattery.com/ebike-kits/633-250w350w-q-85100sx-motor-e-bike-kit.html

My questions:

1. If I buy a bare 500W CST, with no wheel, could I adapt it to the 16'' wheel of the Ori? If not, at least could I adapt this motor to a "standard" 16'' wheel, getting rid of the front Ori wheel then?
2. If not, what would you recommend:
a) Brompton with q85 front
b) Ori with q100c rear
c) Another possibility, such as the first option I was discussing (28'' bike with q100h), a Brompton with MAC or something similar

Thanks.

 

[Deleted member 4366]

Cwah installed a MAC in his Brompton, so it can be done with quite a lot of messing about. the CST is slightly smaller,so that should go in as well, but with a lot less messing about if you use the Ori with standard 135mm. These bigger motors need bigger batteries,so you're going to end up with a heavy bike.If you've got some steep hills, you'll be using about 20wH per minute. Bear that in mind if you're thinking of a small Konion pack.

Most motors are for 36 spokes, so if you don't have 36 hole rims already, get one first. There's different sizes of 16" rims, and the Chines ones are the smallest, which don't fit a Brompton. I don't know about the Ori. It's a shame they don't do disc brake versions because then it wouldn't matter.

Next point: I'm not sure whether the S06S works with the higher speed Q100 motors, or any of them. I have the S06S integrated in a bottle battery,and it doesn't work with a 328 rpm Q100C. It's sensorless, so is different to the one in the aluminium case, so you'll be in the realms of the unknown until somebody tries one,otherwise the KU65 and KU63 will work OK.

From my experience with a Q100 in my Dahon, I'd say that the Q100 has enough power if you don't want to race the lycra clad road-bike riders. The 328 rpm Q100c at 36v will give about 17 mph. If you want more torque and less speed, the 260 rpm Q100H will give 13mph, but you lose the cassette gears. if you want a bit more power with the Q100H, a step up to 12S lipos will bring the speed up to 16mph with a big step in torque as well.

You can also get a nice step in torque from a Q100 by soldering 25% of the shunt in the controller.

The Q85 is smaller and less powerful than the Q100,so would only be my choice if you're stuck with a Brompton.

One thing puzzles me. if you're worried about getting it nicked, why do you want an expensive bike like an Ori or Brompton, surely a cheaper Ebay Chine bike would be better, but don't get one with big beams that come down to the back wheel. It might be too stiff to get the motor in. This one looks OK, and even has a disc mount for the back brake.
http://www.ebay.co.uk/itm/16-WHEEL-LIGHTWEIGHT-UNISEX-ALLOY-FOLDING-ROAD-COMMUTER-BIKE-BICYCLE-20-/190861843660?pt=UK_Bikes_GL&hash=item2c70409ccc

 

[Arbol]

Thanks, d8veh, I appreciate the extensive answer.

Some comments:

1. About "One thing puzzles me. if you're worried about getting it nicked, why do you want an expensive bike like an Ori or Brompton": I would never leave the bike at the street, so it could not be stolen.

2. The idea of having a folding bike is because of space / lack of need to park it in the street. I would use the small wheels to roll the bike when folded, but I would not need to bring it "full weight", so weight does not matter much to me. I could have a big motor and a big battery (a 50V 10Ah at em3ev weights 3.5kg, so it is not too much either).

3. From your answer, you apparently imply that if the wheel has 36 holes (irrespective if it is 16'', 20'' or 28''), it will fit with most motors. Is this interpretation correct? So, if an Ori has a wheel with 36 holes, can I reuse that wheel and order a bare motor, knowing that it will fit my wheel?

4. 12s lipos is I believe 44V. Would a 50V battery work with a Q100C? (50V is the voltage of em3v samsungs, for example). 50V at 15A, which I believe is what a KU65 gives at max is 750W, is that OK for the Q100C? By the way, does the KU65 withstand 50V?

5. What would you believe is best, from the following? (I know there is no best solution for everybody, each person is different, but I ask anyway; assume security against burglars is irrelevant, and usage is urban + some unpaved roads):
1. Q100C rear in 16'' bike
2. Q100H front in 16'' bike
3. BPM (or BPM2 or CST) front in 16'' bike; by the way, a CST works at the front, too?
4. BPM rear in 28'' bike
5. Q100H rear in 28'' bike

 

[Deleted member 4366]

2 Cwah would be the best to comment on that. It seemed to work for him, but I don't know how often he folded it with that big battery strapped to the top. Personally, I don't think that it's a good idea to put a big motor in a small lightweight bike, but each to their own.

3 Correct,. You only have to get the right length spokes. There are some motors that have different numbers of holes, but they're not very common. I have an Ezee motor with literally hundreds of holes in it, so it'll fit just about any pattern in any rim.

4 and 5 There is no best or right answer. You have to choose on the basis of how much power, speed and torque you want. You can use voltage to change the speed up or down:
36v 201 rpm =15 mph in a 26" wheel real world speed on the road with a reasonably charged up battery.
16" wheel = 9mph
From now on all 16":
36v 260 rpm = 12 mph
36v 328 rpm = 15 mph
44v 201 rpm = 11 mph
44v 260 rpm = 15 mph
44v 328 rpm = 18 mph
50v 201 rpm = 12 mph
50v 260 rpm = 16.5 mph
50v 328 rpm = 20 mph

Power = volts x amps (sort of) so 44v will give 20% more power and more torque. The extra torque is difficult to quantify because it's different at different speeds.

Increasing the current from 15 amps to 18 amps gives 20% more torque, which gives higher speeds throughout the range, but doesn't increase the maximum speed.

If you have a motor that is too fast for its power and torque, it'll be inefficient and get hot. The highest speed mentioned above is 20 mph, so should be well within the power of a Q100 at 50v, so you shouldn't get any problems in that respect unless you have serious hills to climb.

 

[Arbol]

Thanks again, d8veh.

If I chose a big motor for a Brompton, I believe I would put the battery inside a front bag, not strapped to the bike. Let's hope cwah comments on this issue, I am interested.

Regarding your comment "Increasing the current from 15 amps to 18 amps gives 20% more torque": I guess this refers to your previous comment "soldering 25% of the shunt in the controller." How can this be done? Is it necessary to be an expert in soldering / welding?

If I chose a Q100 at 50V and at 18A, what would be best in a 16'', front (and then possibly a Q100H) or rear (a Q100C)? I believe most people prefer a rear motor for driveability. But in an Ori, with the possibility of a front bag, all the electrical components could be in the front, reducing the amount of wires through the bike. But maybe the front would be too heavy to drive comfortably?

 

[Arbol]

Other opinions? Up with the thread!

 

[Deleted member 4366]

Soldering the shunt is dead easy. On most controllers it's behind the end-plate, so four screws to remove the plate. take one hot soldering iron and one piece of solder. Place the iron on one side of the shunt to heat it up for a few secs; keep it there while you add a it of solder; use the iron to spread it round the wire; remove the iron; screw back the plate; enjoy your extra power.

Before



After



You might struggle for traction with 50v 18 amps in the front. It'll be OK on the flat, but might spin on hills. It won't be dangerous though.

Now that I think about it, 900w would probablty be too much. 15 amps at 50v should be enough, or 18 amps at 44v.

 

[Arbol]

1. When you say "Now that I think about it, 900w would probablty be too much. 15 amps at 50v should be enough, or 18 amps at 44v", are you refering "too much" for a front motor? Or are you refering to the max power a q100 accepts, either front or rear?

2. A Brompton apparently only accepts a q85 (or similar), but let us assume it does not accept a q100/BPM/MAC (or it is very difficult / not convenient to do so). What would be the max combination of voltage and amperage a q85 would accept? I believe I have read a q85 saturates at around 12A / 13A. Would 12A / 13A at 48V would be ok for a q85? or it has to be a 36V too?

3. In case I finally choose the first option in the first post of this thread (a 28'' stealthy bike, 7spd freewheel), I guess that then I could use more powerful combinations, such as a q100h or a BPM, both rear. I imagine the BPM is more bulky / less stealthy than a q100h. But I guess a BPM2 at 48V with a KU123 at 30A must be a bomb, in comparison to a q100h at 48V with a S06P/S at 15A. What do you think?

 

[Deleted member 4366]

I'm not sure what they've done to the Q100H to give it a higher power rating. It feels like they've only changed the winding speed, but I've only tried them with 15 amps so far. Torque can't be high from small motors, so they'll always be prone to over-heating when they slow down under load. At 900w, you're in the realms of the unknown. As long as you can keep it spinning fast, you should be OK, but all I can do is guess.

The Q85 is even smaller, so common sense says that whatever the Q100 can do, the Q85 will be 15% less.

There's absolutely no comparison between a BPM and a Q100, My bike with a single BPM at 25 amps, climbs better and generally feels more powerful than my bike with two Q100Hs at 15 amps each. Don't forget that a BPM at 30 amps needs a high power battery,and it'll have less than half the range of a smaller motor at 15 amps, so you end up with a much heavier bike. My Dahon with a Q100 at 44v and 18 amps has plenty of power. Hill-climbing is not bad, and it can cruise at around 20mph without pedalling, even up slight hills. The lower gearing of the 16" wheels should make it even betterr if you can find the right voltage, current and speed combination

The Brompton has steel forks, so spread them and fit whatever motor you want. small motors are good if you want light-weight and small power

 

[Arbol]

Interesting.

Then, if the Brompton front fork can be expanded to 100mm and a BPM2 can be fit in, the power would be good. I guess it would be necessary to add torque arms (I believe I read at endless-sphere the case of a guy that broke twice his front fork due to a front BPM).

A combination could be the BPM2 at 48V, an S12P controller (through the package http://www.bmsbattery.com/controller/649-s06-250w-imitation-torque-square-wave-controller.html) and V4 Konions, providing 30A (or an EM3EV Samsung package). That would provide almost 1.5kW. Would it be safe, having 1.5kW "everything front", or could there be annoying consequences of having such a powerful combo on the front of a Brompton?

I am thinking about the combination BPM2 / S12P because it is clearly more powerful than a Q100 / S6P (as you describe), but price is quite similar. The only real difference in price is the battery, but in fact, the difference in price between a 36V and a 48V battery is not that much.

I am not too concerned about weight. For me, the importance of a foldable is size, I do not think I would have to carry the full weight much (I would not use it in combination of train / bus / ... often).

 

[Deleted member 4366]

You'll need twice the size battery with the BPM as you would with a Q100. The Bromton's steel forks won't brake like the other guy's aluminium or magnesium ones did; however, a BPM at 48v and 30 amps will produce masses of torque, so the whole bottom of the Brompton fork would have to be reinforced. You'd be better off buying a spare pair of forks to completely re-work. Cut the bottoms off and weld on your own stronger drop-outs. There's something that I'm not sure of through. The BPM has a larger diameter than a Q100 or SWX.. I'.m not sure if there'll be enough clearance half-way up the fork. Here's a SWX in a Brompton fork. You can see how tight it ison the right side (of the photo).

 

[patpatbut]

That is correct. Dave.

If the motor is too big, there is a big problem when you fold down the handle bar. If you are using S type maybe you can get away from it.

My brompton is SWXB front motor and it takes a lot adjustment to make the brompton fold perfectly.

Pat

 

[cwah]

Get a Mezzo bike. The rear dropout is large enough to put a big motor such as a BPM.

It doesn't fold as small, but it's not bad. It also folds in half very quickly.

With a big motor on the front, and potentially another battery, it will wear the bike quickly when you fold unfold it on the hinges.