The Cycle Stoker is a mid-drive electric assist system for Edgerunner and Yuba Mundo cargo bikes that we developed in early 2013. The design uses the same core components as the classic Stokemonkey system, but it runs a single chain on the right along with a freewheeling patterson crankset to allow motor operation without forcing the pedals to turn.
By clever use of the chain angles and idler pulley locations, we are able to sense the rider's pedal torque via a strain gauge on the mounting bracket and display actual human power output on the V3 Cycle Analyst. This intrinsic torque sensing capability allows for proportional torque control of the motor power level, a feature lacking from the majority of aftermarket mid drive systems.
There are lots of hub motor and mid-drive options for converting a cargo bike to electric assist, and for many people any of these other kits will be more than adequate. But if you are after a system that can turn heads and fulfill some special needs in the cargo ebike space, then this kit might be ideal for you. Here are the things that make it stand out:
- Non proprietary drive-chain: As with the classic stokemonkey, all the gear transmission from the motor to the wheel is achieved using conventional bicycle chain and bike sprockets. That means you have multiple sources for replacement components as there are no impossible to find gears or bits which could fail.
- 2 Speed Front Chainring: The Patterson 2-speed cranskset has a 1:1 and 1:1.65 overdrive mode, giving a similar gear range on the front as a triple chainring without any of the complexities of a normal derailleur. Many popular mid-drives like the Bafang BBS0X only support a single speed chainring, which leaves you with a limited overall pedal gear range when the battery runs out.
- High Speed Capability: We supply the Patterson crankset with a special 39T chainring, which transforms to the equivalent of 62T in overdrive mode. That helps compensate for the smaller 20” rear wheel of the Edgerunner bikes, allowing you to maintain a comfortable pedal cadence even at high cruising speeds. With a 26” wheel bike like the Yuba Mundo, it allows you to keep pedaling the bike even at highway velocities.
- Torque Sensing with Human Power Readout: The Cycle Stoker system accurately senses the human pedal torque via the mounting bracket, which combined with the V3 Cycle Analyst gives you the option for proportional pedal assistance for throttle-free control, and also shows how many watts you as a rider are contributing.
- Normal Pedal ‘Q’ Factor: A lot of mid-drive systems use extra long spindles in order to have sufficient clearance for the motor and other electronics between the cranks; the BBS0X for instance have a 160mm spindle, putting the cranks about 40-50mm farther apart than a standard bottom bracket. This results in a less than ideal penguin like pedal position that can be uncomfortable on the knees.
- Unique Look, manufactured mostly in NA: The Stokemonkey motor we had made overseas of course, but most of the other custom mechanical and electrical parts are made either on our shop CNC machines here in Vancouver or sourced from US based manufacturers (like the Terracycle idler pulley). We’ve tried to make the machined hardware parts as attractive and interesting as they are functional.
Of course, everything has its share of tradeoffs, and there are some downsides to the Cycle Stoker drive which we will detail with equal weight. Here are some things that the Cycle Stoker is NOT
- Super easy to install: The installation of the Cycle Stoker system involves replacing your bottom bracket with the Patterson crankset system, and that requires all the special bottom bracket tools that you’d normally only find at a bike shop, plus using a chain tool to extend the total length of your bike chain. It’s definitely an afternoon project for those who are mechanically inclined. That said the electronics and wiring is largely plug and play, and we have customizes the cable lengths so that the wire runs cleanly follow the frame tubing.
- Inexpensive: At $1495 for the full kit without a battery, the Cycle Stoker is definitely more costly than most hub motor conversions, and is on the upper end of mid-drives. However, if you take a typical conversion in the $500-$800 price range and then add the value of a 2-speed crankset (~$300), Torque Sensing ($200-300 for a typical sensor), a more flexible display like the V3 Cycle Analyst ($150), then you very quickly get to the same ballpark in order to match the same features.
- Lightweight: The total weight of the motor and all mounting hardware and electronics is about 7kg, making it heavier than most mid-drives and comparable overall to a larger direct drive hub motor. Other mid-drives typically use a smaller motor with a much larger gear reduction in order to get similar torque with less weight. The BBS02 drive is ~4.5 kg.
- Totally Field Proven: Even though we’ve had Cycle Stoker systems on the road clocking many km for almost 2 years now, this is still in relatively small numbers. We know from experience that many issues don’t start to show up until you have 100’s or 1000’s of units on the field. So this kit is still a little bit experimental.
- Insanely Powerful: The stokemonkey motor is in the 500-750 watt power class, which is about as much as you want to put through a bicycle’s drivechain. If you want cargo power in the 1-2 kW range or more, we’d usually recommend dual hub motors rather than a mid-drive.
Is it for me?
Our own experience is that for cargo bikes, probably 80% of users would have their needs met more than adequately with a high torque geared hub motor, like the eZee hub motor kits or other large geared motors in this power class (BMC, Bafang BPM series etc,)
Where the mid-drive setups shine is when your trip spans a wide range of speed requirements, going slowly up really steep hills with a heavy load, and similarly going fast on long flat sections and downhills.
How Fast and Far will it go?
These are some of the first questions people want to know and also the most irrelevant in a sense. Being a mid-drive system, the Cycle Stoker is able to provide assistance to the bike over a very wide speed range, whether you are slowly grinding up a hill or flying down it at traffic speeds. But the total power from the motor is limited to about 550 watts at 36V, and 750 watts at 48V. That power limit will determine the ultimate speed that you can achieve in a given weight vehicle and grade of hill. For instance, climbing a steep 10% grade hill with a 250kg vehicle at just 20kph requires 1500 watts of power. If all you have is 750 watts, then expect to go up at more like 10 kph instead.
For the range, that is simply a function of the capacity of the battery pack that you choose. A battery with twice the amp-hour capacity will have twice the range per charge. You may or may not have better energy usage with a mid-drive over a hub motor, that would depend a lot on the circumstances, and the general rules of thumb for wh/km in our battery page apply. .
Will it fit on my bike?
At the moment, we have clampsets for this system on the 2012 and 2014 Edgerunner frames as well as the Yuba Mundo. We developed a system for the Bike Friday Haul-a-day as well, but then their frame design changed to include diagonal cross tubes which interferes with the motor it. We have plans to produce a model for the Surly Big Dummy.
Voltage, Winding Type, and Gearing?
There are two winding options for the Stokemonkey motor, and standard 9 turn wind (8 RPM/V), and a faster 8 turn winding (~9.2 rpm/v). We recommend the faster wind motor with 36V battery packs, and the standard winding with 48V batteries, to provide a good match of the unloaded motor RPM with a normal riding cadence. If you use the standard wind motor at 36V, you might find that the motor only provides adequate torque at low pedal speeds. Similarly, If you like to like to spin the cranks at a very high cadence (>110 rpm), then you might want to use the fast winding at 48V.
Will it work with other cranksets?
In principle the Cycle Stoker system should work with any freewheeling crankset with a single chainring. The Patterson is a great value, but there are a few other 2 and 3 speed cranksets on the market (Schlumpf and Efneo), as well as non-geared freewheeling cranksets made explicitly for mid-drive ebikes.
We do not recommend using a regular non-freewheeling crankset, as any time the motor is powered when the pedals aren’t turning there will be chain slack between the motor and cranks causing the chain to fall off.
Can I purchase without the CA, torque sensing etc?
It is possible to run the Cycle Stoker using just throttle control and no Cycle Analyst or torque sensing, although you then miss out on some of they key benefits of this system. For that, please contact us directly about doing a modified kit.
Does it require a Nuvinci Hub? What other hubs can I use?
We had our first run of Cycle Stoked Edgerunner Ebikes built up with Nuvinci hubs on the rear, and the combination works quite well allowing for an infinitely adjustable gearing that can be shifted under load. However, the lower efficiency of the Nuvinci transmission (~85%) somewhat negates the motor efficiency benefits of a mid-drive system.
For the best efficiency, either regular derailleur gears of the Rohloff internal hubs are recommended. Other internal hubs may work, provided that they are guaranteed for tandem bike use and hence are designed for more torque than just a single rider. Most internal hubs are designed for light duty usage and will fail catastrophically in this application of combined human and motor power levels.
Link to Yuba guide
Link to Edgerunner guide
Link to CA3
Recommended CA Settings
We will usually pre-load the Cycle Analyst for torque control mode with a 3 position switch to set between 0%, 50%, and 100% assist levels. However, several settings must be customized with each installation because of unit to unit variations in the torque sensor.
The idea behind the Cycle Stoker drive layout came from varied discussions with Todd Farhner, the inventor of the original Stokemonkey. While brainstorming ways of to have the stokemonkey motor drive a right side chainline, we realized that with minimal modifications, the stokemonkey bracket could take an idler pulley that would allow for proper chainwrap around the counterclockwise spinning motor. And that, with some updates to the bracket attachment point we could potentially measure the rider’s pedal force with a stationary strain gauge.
We built several prototype bikes in early 2013, and then field tested one of these on a Vancouver to San Francisco ebike trip before bringing it into tentative production by the end of the year. Both the trip and the design and development details are documented on this endless-sphere thread. For most of 2014 we were selling the Cycle Stoker only pre-installed on Edgerunner bikes with a Nuvinci hub drive in order to work out the design kinks, prior to adapting it to the somewhat different frame geometry of the 2014 bikes and releasing it as an independent kit.