Regen

All About Regen Video

The video above covers most of the details. The sections below go deeper on what regen is and the different ways to activate it.

What is Regen?

Regenerative braking means using the electric motor as a brake to slow down a vehicle, and is one of the unique features of electric propulsion. It not only provides a zero-maintenance, perfectly consistent braking force in all weather conditions, but it also captures this braking energy and puts it back into the battery pack, rather than burning it all off as heat. This not only increases your range, but it also encourages safer riding habits as you know energy isn't being wasted every time you use the brakes.

In principle regen is available on any system with a direct-drive hub motor or a geared hub motor that does not freewheel. However, it does require a motor controller that supports regen, and many budget controllers either don't or don't support it very well. That may be one of the reasons that regen isn't widely appreciated in the ebike scene and is often even dismissed outright.

For us, regen has been one of the most alluring aspects of ebikes from our earliest days building prototypes out at UBC, and understanding regen was one of our main motivations for making what later became the Cycle Analyst.

Is it Worth It?

For a lot of our customers, regen is one of the best parts of running a direct-drive hub motor, and one of the reasons we favour hub motors over mid-drives, which have essentially no path to regen. The range it recovers is actually the smallest reason why. The bigger wins are practical:

• Your brake pads last far longer. Because the motor does most of the slowing, your mechanical brakes go from a regular wear item to something you barely touch. On a heavy or fast ebike, that alone is worth a lot.
• Braking is consistent in every condition. Electronic braking does not fade in the rain, on a long descent, or as the pads wear, and it feels the same every time.
• You can hold a speed downhill. With proportional or speed-limited regen you can descend a long hill at a steady pace instead of riding the brakes the whole way down, which is far more relaxing.
• It simply feels right. Slowing down while watching energy flow back into the pack, instead of throwing it away as heat, is one of those small things that makes an ebike feel smart.

The one catch is that regen only works on a direct-drive motor, not on a normal freewheeling geared hub. The good news is that on a direct-drive motor it comes for free: if you are running one of our All-Axle kits, our most popular setup, the capability is already built in, and it is just a matter of choosing how you want to activate it from the options below.

Range Increase

How much range does regen actually add? On a typical ride with a Grin direct-drive setup, expect it to recover somewhere in the range of 3 to 8% of your energy. It is not a huge number, and on flat, steady riding where you rarely brake it is close to zero. But in hilly terrain or stop-and-go city riding, where you brake often and descend long grades, the recovered energy adds up and the higher end of that range is realistic. Think of it as a modest bonus on top of regen’s bigger everyday benefits, rather than the main reason to run it.

The heavier the vehicle and the more you brake, the more you get back. On a loaded cargo bike or a recumbent trike the numbers climb: one of our staff riders gets about 20% of their energy back from regen on a recumbent trike and has not changed a brake pad in over 8,000 km.

How is Regen Activated?

In order to engage regen, the motor controller needs some type of signal telling it that the rider wants to brake. Depending on the signal type, this can result either in a fixed braking force, or a proportional force that can be modulated in intensity.

1. Ebrake Lever: Most regen-enabled motor controllers have a digital ebrake input plug, and when the brake lever is pressed this results in a fixed regen intensity. That works better than nothing, but the inability to adjust the braking force limits the amount of gain from regen and the mechanical brakes still come into play.
2. Ebrake Lever + Throttle: In order to have some way to modulate the regenerative braking force using existing ebike hardware, we had the idea back in 2007 to have the throttle switch behavior from controlling motor torque to braking torque when the levers are active. This takes advantage of existing hardware already on the handlebars to provide variable braking force. It is not immediately intuitive to use the throttle for braking, but you get used to it quickly. This approach was featured in both the Cross Canada ebike and the first-generation Grinfineon controllers.
3. Separate Regen Throttle: Many EV controllers support an analog brake input signal that can be mapped like a throttle, so in a pinch a rider can install two throttles on their ebike. One of them controls acceleration, and the other controls braking force, allowing for a smooth modulation from zero to full regen. In theory this regen throttle could be in the form of an ebrake lever with a proportional signal instead of a simple on/off switch, but such levers are not readily available on the mass market.
4. Bidirectional Throttle Signal: In all of the Grin motor controllers (Grinfineon, Phaserunner, Baserunner), we have mapped the otherwise unused portion of the throttle signal below 1.0V to activate proportional regen control without any additional wires. Throttle signal voltages from 1.2V to 3.6V provide proportionally more power, while if that same signal drops down to 0.8V it starts doing regen, increasing to a maximum regen intensity at 0.0V. This would in theory allow for bidirectional throttles that can be twisted one direction for power and in the other direction for regen. We had long heard of such throttles existing but never seen one, so we now stock two of our own, both terminated in a 3-pin Higo waterproof plug and compatible with our Main9 harness kits. The affordable option is a bidirectional twist throttle; for a nicer feel, the modified Dyol bidirectional throttle comes in left-hand and right-hand versions. 
5. Speed Limit: Some controllers allow for regen to engage at a certain speed and vary in intensity to keep the bike from exceeding a speed limit. This behavior is especially nice on hilly terrain and allows for proportional regen to kick in automatically on the downhill sections with no user input.
6. Back-pedaling on a PAS sensor: Quadrature-based PAS encoders have the ability to tell when the cranks are being spun backwards. This is implemented in the Version 3.2 Cycle Analyst firmware.
7. Up/Down Level Control: A fixed amount of regen can also be activated on some systems using the up/down buttons for setting assist levels. This provides a nice way to enable steady regen on long descents, and is provided in the V3.2 CA firmware as well.

Regen at High Speeds from Back-emf Voltage

You will also get braking force from the motor, and current flowing into the battery pack, whenever the bike is moving faster than the unloaded speed of the motor. This happens whether you want it to or not, because the mosfets in the motor controller have body diodes that cannot help but conduct current once the back-emf voltage of the motor exceeds the battery voltage.

This can be used as a deliberate feature to build an ebike that naturally governs its own top speed. It can also be a nuisance for riders who want to coast fast down a hill without the motor holding them back. That scenario can be addressed with our Phaserunner or Baserunner controllers via field weakening, which raises the effective unloaded motor rpm.

Getting Started with Regen

Regen comes built into every direct-drive kit we sell, including our most popular All-Axle kits. Once you have a regen-capable motor, turning it on is just a matter of picking one of the methods above, from a simple ebrake lever to a bidirectional throttle.

Related reading: Why Hub Motors Are Awesome · Bike Compatibility · Connector Guide