Installation of the new BMC Puma 450 watt geared bicycle hub motor

Your fearless Cycle 9 staff is constantly on the watch for new types of motors/bikes/gear. One item that caught our eyes recently was the BMC “Puma” hub motor. This mysterious beast has been seen occasionally out in the wilde(sic), but not too many people seem to know much about it.
We decided to check it out, since on paper it looks very nice:
– Brushless 450W nominal, 800W peak rated power
– Internally geared 4.8:1 drive system, that means increased torque in a smaller package
– Light weight compared to e.g. Crystalytes and Forsen motors
– It comes from a reputable motor manufacturing company. They make industrial motors for all kinds of applications.
– Included thumb throttle with basic battery status indicator
– 25A controller with low voltage battery protection, and waterproofed thoroughly (the electrical components are embedded in so-called potting material, which is impenetrable by water). Designed for 36 or 37 volt nominal battery systems.
– Good cost.
We ordered a few up, built the wheels, and Morgan installed one on an Xtracycle equipped bike. Here are some pictures of the installation:
Bare motor after wheel build:
BMC Puma motor before install

Installing freewheel (this one is a six speed, but it can take up to eight):
BMC Motor freewheel installation

Freewheel installed with the three washers: dropout positioning washer (a rudimentary torque arm), flat washer, and lock washer:ahh, fresh, unused, clean gears

Installing rim tape to prevent spoke holes in tube. We like cloth rim tape.
Installling rim tape on the BMC geared motor
Bike with Xtracycle upside down, ready for BMC hub motor:
Bike with Xtraycle upside down ready for BMC

Tightening down the axle bolts. Make sure to get them very tight, or spinouts can occur, which can tear the phase wires. Also, make sure washers are totally flat against the drop-out area. If not flat due to some protrusion, you’ll either need to use a different/smaller washer, or use a tool (e.g. Dremel) to grind down the protrusion on the dropout
Mounting BMC Puma motor on bike

This shows the derailleur side, with a six speed freewheel (up to eight are usable with the BMC):
Six speed freewheel on the BMC hub motor

Controller, taped to the stay of the Xtracycle. It is good to mount the controller outside, against the frame, because the frame acts as a heat sink:BMC hub motor controller taped to stay

Plugging everything together. This shows the primary motor phase wires being plugged in. There is only one way this connection will fit together (the right way!):Plugging connections for the BMC

Installing the thumb throttle. The BMC kit comes with a standard thumb throttle that includes a power light and basic battery charge indicator light. The install is pretty straightforward, though with certain types of shifters, there can be interference issues that need to be worked out. Picture shows tightening down the set screw with a 3mm hex key:

After putting a new wheel on, usually it is necessary to re-adjust the rim brakes for correct alignment and toe-in. If you ignore this step, the pads may squeal, or worse, rub on the tire and destroy it. This step does not apply to disc brakes (there’s a different set of issues with those). The BMC does come ready for disc brakes, though we haven’t yet tried that feature.

The installed BMC 450W Puma motor in the Xtracycle Freeradical:

The bike put back together. Note that it still has my original (large) Crystalyte controller as well. I took that off later after confirming that the BMC controller did indeed work:

I’ve now used this on my bike for several days, including daughter carrying, and other moderate loads. I have about 40 miles on it so far. I am powering it with some Lithium Iron Phosphate (LiFEPO4) batteries at present.

Overall, I am impressed. It has good torque and good hill climbing. It is very efficient, and quiet. My watt-hours per mile are pretty low using this – around 13 wh/mi the first 20 miles, then around 16 for the last 20 (when I was carrying my daughter and in a hurry). It is very similar in overall “feel” to the eZee, though perhaps a bit more quiet. I’m not so excited about the thumb throttle, just because I prefer twist throttles. But installing a different throttle should be straightforward. Anyway, I didn’t measure the weight before putting it on the bike, but it feels very similar to the eZee, which is around 10 lbs for motor + wheel (significantly lighter than Crystalyte motors). I will measure the weight of the next one we build up.

Top speed was actually a bit better than expected, depending on the voltage of the battery pack (i.e. whether it was just charged, or not). At 38V, the top speed was around 23 mph, and at 34V, it was more like 21mph. The power curve “feels” fairly flat (a good thing). For two days’ riding over hilly terrain, on the Xtracycle, carrying my daughter (45 lbs) half the time, I averaged just shy of 18mph (including a fair number of stop lights and signs). That is a respectable number.

It does have a “soft-start” feature, meaning that when the throttle is activated, it takes 1/2 second to start going, and then ramps up a bit slowly at first. This was apparently implemented for safety reasons (and it also helps conserve battery). Some customers will like it, others will hate it. For those who don’t like it, we’ve been informed that it is a simple modification to the controller to get rid of it, and let the motor just “take off”.

The only issue I noted on the first day was that when the battery voltage got low (< 31 V), the motor seemed to "chug" or struggle. I think this was the low voltage cutout happening to protect the battery. It only happened at higher currents (> 13A). It was possible to avoid it by taking it easy on the throttle. That’s probably a good idea anyway when the battery is getting low (especially NiMH or lead acid, which can be damaged if over-discharged).

For the technical crowd, peak Amps from the controller was ~21, and peak Watts was about 790. This is a nice mid-power range.

We are building these up with beefy 2.0 mm spokes, brass nipples, and Sun Rhyno Lite wheels. We like these wheels because they are pretty solid and cost effective.

Now, for those patient or interested enough to wade through all that, here’s the scoop on availability. We will be selling some in limited quantities at an introductory price of $550, for wheel/motor, controller, and throttle. After we are happy that all is good with these, we’ll raise the price. To get one at this price, you’ll need to convince us that you can handle a “beta test,” meaning that until we have more experience with reliability, there could be down time or other issues. We’ll of course back up problems with warranty, but we can’t guarantee that we’ll be able to Fedex you the fix by the next morning. You’ll also need to be technically inclined enough to do installation and basic troubleshooting (or, if you are a local customer around the Triangle, we can do that stuff).

Right now, we have 3 of the rear motors available, two being built into 26″ wheels, and one into a 700C wheel. If you want to get your hands on one, please drop us a line. We’re pretty excited about having another nice, lightweight geared hub motor to offer. And if it stands the test of my use, that’s saying something… (I am pretty abusive on gear, and also picky).


4 thoughts

  1. what are the advantages/disadvantages of using the rear wheel motor versus the front?

    Also, that Kidz Tandem in the shop looks very fun!

  2. Hi Dave,
    This is a good question that I should add to the FAQ, but briefly:

    – Front motors are generally easier to install. No messing with gears, cog clearance, etc.

    – For a short wheelbase bike, a front motor can help with weight balance if you have a battery pack and/or your gear on the back

    – If you have cheap, cast aluminum forks, they may not withstand the stress of a front motor. In that case it is good to install a rear motor, or to replace your front fork with a chromoly steel one.

    – A rear motor is usually a bit more “stealth” for those who don’t want it to be obvious that they have an electric motor

    – Most rear motors (except BionX) are limited to 8 speeds due to clearance issues. All the rear motors use freewheels, not cassettes. We need to explore the potential for the BMC to accept 9 speed, but I kind of doubt that it will. Also, rear motors don’t work with a bike that has internal hub gears, like the Shimano Nexus.

    – A front motor can make the steering feel a bit heavier/slower. With the lighter geared motors (like eZee, BMC) it is not so bad, but with heavier motors like Crystalyte and Forsen, it is noticeable. Some people don’t mind, others do.

    In the end, it really depends on your bike, and how you use the bike, to determine the front/rear installation question.


    ps – and yes, the KidzTandem is a lot of fun!

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