All-Axle Hub Motor

The Grin All Axle Hub Motor

All Axle Hub MotorsCAD Model of Grin All Axle MotorThe All Axle motor is a direct-drive front hub that we designed to be universally compatible with all the variety of quick release and thru-axle front fork standards that exist in the bike world these days, as well as many single side mounts for trike and quad vehicles. The round hollow axle means that the motor produces no spreading forces on slotted dropouts, and instead is able to transfer all the torque safely to the fork blade via a built-in torque arm.

 

Features

The All Axle motor has the following characteristics:

  • 4.0 kg motor weight (vs >6kg for comparable generic DD motor)
  • 0.35mm Laminations for low motor drag when pedaling unassisted
  • Integrated Torque Arm with secure fork mounting clamp
  • Fits All Forks (regular quick release, QR12, QR15, QR15 Boost, QR20, and even 150x15 fattbike) through the use of simple adapters
  • Compatible with Single Side Installation on many trike and quad vehicles
  • Uses 32 Spoke Holes for vastly more in stock rim options
  • 18mm Disk Caliper Clearance fits most (but not all) calipers without spacers
  • Statorade Compatible with side cover injection port
  • Available in both metallic silver and black anodized finish
  • Designed and Assembled in Canada

Axle Adapters

The stock Grin motor axle is 95mm long with a 20mm hollow center, and then uses a series of axle inserts and end caps to accommodate different installation geometries

 
Quick Release
These inserts allow the motor to fit in standard front forks with slotted dropouts using a regular quick release skewer to hold the motor in place. The vast majority of older bikes and new low to mid-range bikes will use this adapter

QR12
The 12 mm thru-axle is a relatively new standard for road bikes to gain the stiffness and security benefits of a thru-axle wheel at a lower weight than the 15 and 20mm sizes common in mountain bikes. These hubs have the standard 100mm dropout spacing.

QR15
The 15mm front thru-axle was introduced for cross-country and mountain bikes when the original 20mm thru-axle standard of downhill bikes was seen as overkill. The regular 15mm thru-axle uses the same 100mm hub spacing and disk rotor placement as regular quick release hubs

QR15x110 Boost
These adapters are similar to the standard QR15 except that the right side insert protrudes an extra 10mm, making the overall hub 110mm wide instead of 100mm for wider flange spacing.
QR15x150 This is a new standard with a 150mm spacing between the fork to accommodate the wide 4"-5.5" tires seen on many fatbikes these days. The Grin Motor inserts for the 15x150mm fatbike screw onto both the left and right sides of the axle to provide extra length, while a spacer on the disk mount repositions the rotor to the correct location

QR20
This is the original thru-axle fork standard created for downhill mountain bikes and popularized in the early 2000's. It is still in common use on large travel suspension forks for serious off-road machines, but has been mostly replaced by QR15 size in regular mountain bikes. These Axle Adapters space both the left and right sides equally to build up the extra 10mm length. To fit the "20mm Boost" forks, a simple 5mm spacer is mounted under the disk rotor to position it closer to the fork.


With all of these adapters, a separate torque arm is installed on the right side of the motor axle. A mating frame clamp secures to the fork blade with a pair of hose clamps and the two parts or locked together with an M5 bolt. When the motor needs to be removed, this bolt is loosened and then the arm can slide freely downwards as the wheel is taken off.

Motor Speed

The Grin All-Axle Motor is currently produced with three different windings; a slow 8 turn stator, a standard 6 turn stator, and a fast 5 turn stator. All three motor winds are capable of producing exactly the same torque and power outputs so the recommended motor model depends on youre desired vehicle speed. The faster wind motors are more appropriate for small wheel diameters and/or lower battery voltages, while the slower motor winds are more common with larger wheel sizes and higher battery voltages.

The following table shows the unloaded speed of each motor winding at common battery voltages in 20" 26", and 29" (700c) wheel sizes.

  Slow 8T Wind (7.5 rpm/V) Standard 6T Wind (10 rpm/V) Fast 5T Wind (12 rpm/V)
  20” Wheel 26” Wheel 29” Wheel 20” Wheel 26” Wheel 29” Wheel 20” Wheel 26” Wheel 29” Wheel
36V Battery 26 kph 34 kph 37 kph 34 kph 45 kph 50 kph 41 kph 54 kph 60 kph
48V Battery 34 kph 45 kph 50 kph 46 kph 60 kph 67 kph 55 kph 72 kph 80 kph
52V Battery 37 kph 49 kph 54 kph 50 kph 65 kph 72 kph 60 kph 78 kph 87 kph
72V Battery 52 kph 67 kph 75 kph 69 kph 90 kph 100 kph 83 kph 108 kph 120 kph

 

The top speed under any kind of load is going to be less than this value, and we recommend using our motor simulator for exact performance details of any given combination of motor, battery voltage, and controller model.

 

Motor Power

The Grin motor uses a 27mm wide 205mm diameter stator and has similar continuous power and torque capabilities as other direct drive hub motors with this size. However being optimally designed for weight reduction it has less metal mass to absorb heat. Under heavy loads the core temperature will rise at a faster rate than you would see on an otherwise identical but heavier hub, and for those reasons we recommend Statorade in the motor when used in more demanding applications.

The table below shows both the continuous and 5 -minute power capability of the motor at various RPMs with and without Statorde motor coolant.

Output Power Capability of All Axle Hub Motor to 110oC Core Temp
Wheel Speed Without Statorade With Statorade
Continuous 5 Minute Continuous 5 Minute
100 RPM 250 W 500 W 340 W 575 W
200 RPM 560 W 1040 W 785 W 1235 W
300 RPM 900 W 1590 W 1275 W 1830 W
400 RPM 1250 W 2110 W 1840 W 2420 W

 

For a more detailed understanding we recommend using our motor simulator or trip simulator applications to properly predict the capability of this motor in any specific usage scenario.

 

Single Side Applications

Catrike electrified with two Grin All Axle MotorsA unique feature of the All Axle hub design is its ability to work in applications requiring a single side mount. This allows the side wheels of trikes and quads to be readily electrified for the first time, and is especially popular with tadpole trikes running an internal gear hub rear wheel.

Unlike front bicycle forks where there are industry standards (admittedly a lot of standards, but standards at least), the wheel mounting strategy on trikes is all over the map, and unique adapters are required for most vehicle models. We've taken the approach of using the disk caliper mount as an anchor point to hold the wheel and lock the axle against rotation.

Catrike The popular catrikes are ideal for the Grin Hub motor because they already use a 20mm spindle, and they adopt the rear ISO2000 disk caliper mounting standard for both the left and right wheels. For these vehicles we produce a single piece adapter that works on both sides
  Other models of trike have a very similar wheel mount as the Catrikes but have the left side being a mirror image of the right. That requires the use of special mirror image disk calipers. To accomodate these vehicles we've produced a mirrored version of the catrike arm.
Terratrike The terratrike rovers also have a 20mm spindle, but they use a front ISO disk mount and the shaft has a shoulder that prevents the hub from sliding on as far as would be ideal. We accomodate the terratrike axles with a two piece torque arm that provides the necessary spacing for where the motor fits in place.
Greenspeed The Greenspeed trikes use a smaller 12mm diameter spindle and have a disk caliper location that is further away from the hub center than the ISO standards. We have a similar 2 piece arm that can be flipped 180 degrees for working on either side. This also requires a shim to step from the 12mm spindle to the 20mm ID of our hub.
DIY The splined arm used on our Terratrike and Greenspeed adapters is available by itself for doing DIY mounts on other vehicle types. The two bolt holes allow you to interface with a separate flat plate of metal that can attach under the disk caliper or other frame location on the frame to lock the axle from spinning.

 

One Side or Both?

Terratrike with Single Side Motor Drive, works JUST FINE. Image thanks to George HaycraftA trike with dual Grin hub motors can be insanely powerful and will be able to rocket up the steepest hills with amazing efficiency, but it is also quite expensive to do a full conversion with two specialized motors and motor controllers. You can also run a tadpole or delta trike with just a single side wheel motor and leave your original wheel on the other side. In general this does not result in any lopsided steering or handling issues and allows for a ligher weight and more economical conversion.

 

Differences between V1 and V2

The original V1 All Axle hub motor was in limited production from 2013 until early 2019 and used a large 45mm ID thin section bearing on the side covers. This allowed for a generous amount of room for the heavy gauge phase wires to pass through the axle, but the thin section ball bearings could have short lifespans in setups with frequent exposure to the elements.

In the spring of 2019 we released an updated V2 Grin motor design based on feedback and experience. This updated model has the motor cable exiting on the disk side of the motor rather than the non-disk side to facilitate single side installations, and it uses a wider 35mm ID ball bearing standard with a custom tooled lip seal to prevent ingress and egress. These changes increased the overall motor weight a small amount, but the improved robustness and versatility was worth it.

 

Differences between V1 (2013-2019) and V2 (2019+) Grin Hubs
Property V1 V2
Main Bearing 45x58x7 (6809) 35x55x10 (6907) 
Bearing Seal Standard Dust Seal Double Lip Seal
Cable Exit Non-Disk Side Disk Side
Torque Arm Non-Disk Side Non-Disk Side
Connector Anderson +JST SM HiGo L1019
Side Plate Seal Sillicone Sealant O-Rings
Statorade Compatibility So-so (can leak through bearings) Excellent
Weight 3.95 kg 4.05 kg
Magnets N35UH N40UH

 

In addition to the mechanical changes we also updated from N35 to N40 grade magnets. Stronger magnets allow the motor to produce more torque for hill climbing with less heat loss, but they also increase the drag of the motor when riding without power. In our original design we erred on having lower rolling drag because at the time we felt this was more important than efficiency on hill climbs, but the Virtual Electronic Freewheeling feature in the Phaserunner/Baserunner controllers has shifted the balance and we switched to a higher strength magnet.

 Measured Drag Torque of Grin Hub Prototypes with Increase Magnet Strength

As a result the V2 motors spin about 5% slower than the V1 models. They have about 10% more drag torque but they can also climb hills with 10% less heat generation.

Technical Specifications

 

  Slow (8T) Standard (6T) Fast (5T)
kV 7.5 rpm/V 10.0 rpm/V  12.0 rpm/V
Phase to Phase Resistance 268 mΩ 145 mΩ 100 mΩ
Phase to Phase Inducatance 680 uH 380 uH 260 uH
Hysteresis Drag Torque  0.45 Nm
Eddie Current Drag Torque  0.0005 Nm/rpm
Spoke Flange Diameter  214 mm
Flange Spacing  49 mm
Magnetic Pole Pairs  23
Motor Weight  4.05 kg (8.9 lb)

  3D IGS File of V2 Motor

  CAD Drawing of Grin Motor

 

Videos

Background

The All-Axle motor has been a long development project for Grin to produce a direct drive hub motor that was lightweight and compatible with all Thru Axle and quick release fork standards. The idea first took roots in 2010 when we were impressed with the performance of large diameter direct drive hub motors being imported from china, but increasingly frustrated with the poor mechanical tolerances and bike fitment. While prototyping these mechanical improvements we also saw considerable opportunity to reduce the mass of the hub without affecting the torque output.

These earlier videos filmed from Ken (owner of a Calgary based ebike store) as he was passing through town in 2010 show the early development and thought process:

Since then we've gone through a number of design revisions, enhancements, mold toolings, and several pilot production batches while working out many kinks along the way. The hub was really put to the test in several touring trips (such as 2013 cargo biking Vancouver to San Francisco, and the 2018 Sun Trip solar bike race) and has finally come of age in 2019 with the V2 model when we switched to a wider and more rugged bearing, cable exit on the disk side, and a move to o-ring seals rather than silicone sealant for the side plates and screws for more consistent mass production and easier servicing. 

Where to Order

The Grin All Axle hub motors are currently manufactured to order with roughly 7-10 day lead times. As a result, they do not show up as "in stock" on our website, you will need to place an order first even though it says "backordered" in order to have your motor place in the production queue.