GRIN TECHNOLOGIES Fat Front All-Axl Motor Build
FAQs
- Q: Can the motor be used with both thru-axle and quick-release fat bike forks?
- A: Yes, the motor is compatible with both thru-axle and quick-release fat bike forks.
- Q: Where is the motor manufactured?
- A: The motor is made in Vancouver, Canada by Grin Technologies Ltd.
Introduction
Thank you for purchasing the universal V3 Fat Front All-Axle hub motor from Grin Technologies. This efficient and robust direct-drive hub motor fills a void in the market for fat bike fork compatibility and will provide years of service.
Features of the Fat Front All-Axle motor include:
- Lightweight for its power class (5.95 kg vs typical 8-10 kg)
- Compatible with thru-axle and quick-release fat bike forks
- Integrated torque arm for secure installation
- Waterproof L1019 controller connector for hall and phase leads
- Embedded thermistor for motor temperature sensing
- Capable of over 120 Nm peak torque, and 40-60 Nm continuous
- Made in Vancouver, Canada
Components
In addition to the hub motor itself, the motor package will include additional hardware such as disc spacers, axle end caps, axle extenders, and of course, a torque arm. These are identified below:
Axle End Caps
The axle end caps fit inside the ends of the axle to provide the correct spacing and termination for either quick release or 15mm thru-axle spindles.
Axle Extenders
The 135×9 and 150×15 fat bike adapter kits include a short axle extender which increases the effective axle length on the left disc side of the hub for proper 135mm and 150mm spacing. Without an extender, the axle is 120mm long.
Disc Spacers
The standard installation includes a 2mm disc spacer for alignment of the rotor 15mm inside the dropout. An additional 5mm disc spacer is included for forks with a 10mm spacing from dropout to rotor.
Torque Arm
The torque arm is a pivotal part of the motor system that transmits all of the motor torque safely to the bicycle fork without putting any spreading force on the dropouts. It uses a snug splined interface that can withstand tremendous spinning force from the axle, with virtually no play when the torque direction alternates during regenerative braking.
Frame Clamp
The swiveling frame clamp provides a versatile attachment point for the torque arm to connect with the fork blade via a pair of hose clamps. Once the frame clamp is installed, it can stay in place allowing the torque arm to detach with just a single fastener.
Figure 3: Frame clamp can both swivel and slide in and out, allowing correct alignment over a range of fork geometries.
Installation
Before mounting the motor to the bicycle fork you may first need to install the hardware adapters onto the hub.
Axle Extender
Fit the axle extender over the non-disc side of the axle. It is a tight fit and may need to be tapped on.
Torque Arm
Orient the torque arm on the axle such that the cable points down when the arm is pointing up.
This torque arm + extender assembly is held snugly in place with a total of 12 M3 screws, 6 longer screws that pass through the torque arm, and 6 slightly shorter screws for just the axle extender. All 12 screws should be tightened to 1 Nm.
Disc and Disc Spacer
Some fat bikes forks will have correct disc rotor alignment with the 2mm disc spacer which places the rotor 15.5mm from the inner dropout face. This is the same standard as a normal REAR hub. Other fatbike forks expect the disc rotor positioned 10.5mm from the dropout face which is the norm for front forks. In this case, both the 2mm and 5mm spacers are used and a longer M5x16 rotor bolt is required to secure the stack.
The disc rotor screws should be fastened to 7 Nm of torque using a T25 torx driver.
Axle End Caps
Insert the left and right side end caps into the axle. These pieces are held snug with a small O-ring to provide sufficient friction that they stay in place when the wheel is removed from the bike.
Wheel Insertion
The completed hub motor can now be dropped into the bicycle fork just like any other front bicycle wheel. This is easiest with the bike upside down. Carefully place it into the fork, aligning the disc rotor between the brake calipers, then loosely secure the quick-release or thru-axle spindle.
Attaching the Frame Clamp
The frame clamp attaches to the fork blade with two hose clamps. A piece of rubber sleeve is included which can be cut to length and slipped over the hose clamp band to make this hardware more discreet.
Align the frame clamp with the torque arm and tighten up both the M5 nut and the hose clamp bands using the included socket wrench. Tighten the M5 bolt linking the torque arm to the frame clamp with a 5 mm Allen Key. With the torque arm now oriented, you can fully tighten the thru-axle or quick release. When removing the wheel in the future, simply loosen the single M5 bolt linking the torque arm to the frame clamp and the torque arm will slide out.
Controller Hookup
If you have a Phaserunner or Baserunner controller from Grin terminated with an L1019 plug, these parts simply plug together on the forklade. The details of configuring your motor controller and/or Cycle Analyst are covered in their respective manuals. If you are using a third-party motor controller, then it is up to you to either terminate your controller with a matching plug or cut off the L1019 plug and solder on connectors that match your controller. Grin does not provide installation support for third-party controller integration. All pertinent information required for doing this is in this document.
Power and Speed
The Fat Front All-Axle motor is available in 2 different winding speeds to achieve the required performance over a range of battery voltages, wheel diameters, and target cruising speeds.
| Motor SKU | Name | Turns | Kv |
| M-AA4504R | Standard Winding | 4T | 9.0 rpm/V |
| M-AA4505R | Slow Winding | 5T | 7.2 rpm/V |
Table 1: The two winding speed options.
No-Load Speed Table
The unloaded speed for each winding at different wheel diameters is summarized in Table 2. This is the no-load speed it will spin at with the wheel off the ground; actual cruising speeds will be 10-30% less than this depending on the vehicle loading. Please use Grin’s online motor simulator tool to better understand the effect of vehicle type, hill grade, and rider weight on the fully loaded speed.
| Battery Voltage | Slow (5T) Wind | Standard (4T) Wind | ||
| 20” | 26” | 20” | 26” | |
| 36V | 24 kph | 31 kph | 30 kph | 39 kph |
| 48V | 32 kph | 42 kph | 40 kph | 53 kph |
| 52V | 35 kph | 42 kph | 43 kph | 56 kph |
Table 2: This is how fast a given system will spin at full throttle with the wheel lifted off the ground and facing no resistance. The actual speed under any kind of load will always be less than this and is fully detailed on our Motor Simulator web app.
In general, the faster windings are used in smaller wheel diameters or lower voltage batteries, while the slower windings are better suited to larger rims or higher voltage packs. But there is no problem doing fast motors in big wheels or slow motor winds in small wheels if that provides the performance you want.
Winding Speed vs Torque
Note that a faster motor winding does not mean a lower torque motor. However, it does mean that a higher phase current is required to achieve a given torque, and the current handling capability of the L1019 connector will become a bottleneck to high currents. We recommend the slow motor winding if maximizing the peak motor torque output is a primary goal. Alternatively, cutting off and replacing the L1019 plug with a higher current connector will allow similarly high torques with the standard speed winding.
Short Term and Continuous Power
The power output capability of an electric motor is highly variable and depends on both how fast the motor is spinning and how long it needs to run. Table 3 summarizes the estimated output power the Fat All-Axle hub can sustain both continuously and over a 5-minute period when the maximum allowable core temperature is defined (somewhat arbitrarily) at 110C. This table assumes a 20C ambient air temperature and that the motor has a passing airflow consistent with being in a 20” diameter wheel.
|
Wheel Speed |
Continuous Power | 5 Minute Power | ||
| Dry | w/Statorade | Dry | W/Statorade | |
| 70 rpm | 250 W | 600 W | 600 W | 660 W |
| 100 rpm | 370 W | 840 W | 860 W | 950 W |
| 200 rpm | 840 W | 1600 W | 1700 W | 1950 W |
| 300 rpm | 1330 W | 2500 W | 2600 W | 3000 W |
| 400 rpm | 2200 W | 3400 W | 3500 W | 4100 W |
Table 3: The motor power capability depends heavily on the motor speed. That’s why it is better to characterize motors by their torque capability than their power output. As long as the control system is set up to measure the motor temperature and rollback power when it gets too hot, there is little harm in pushing high power levels through the motor. Note that this table is based on the motor itself and does not include limitations that may come from the L1019 connector or the controller. The 5-minute power ratings involve phase currents that exceed 60-70 amps and will potentially melt the L10 plug, likely well before the motor itself becomes overheated.
Official Rated Power
As both the designer and manufacturer of this motor, Grin has full discretion over the ill-defined concept of an official power rating, which can be any point in tin previous table. For the EU and Eurasia, we define the rated motor power as the maximum continuous output before thermal rollback in a worst-case scenario of a slow 70 rpm (approx 10 kph) hill climb. As per Table 3, this is 250 watts. For Canada, we define the rated motor power as the maximum continuous output in a more modest hill climb at 120 rpm wheel speed, which is 500 watts. For the USA, we define the rated motor power as the general continuous power capability at 15 mph cycling speeds (~180 rpm), which is 750 watts.
Storage Injection
As shown in Table 3, motor performance at high loads is increased significantly by the addition of 10 mL of Statorade ferrofluid which helps conduct heat from the stator core to the motor ring. If you routinely see core temperature exceeding 100°C, we highly recommend adding 10 mL of Statorade to extend the usable power window before thermal rollback .Storagee is injected into the motor from a small M3 screw hole located on the right side plate. Add Statorade with a syringe tip with the hole on the bottom so that the fluid flows directly downwards and into the rotor magnets and avoids flowing over the motor bearings and torque sensor. Remember to put the screw back in to seal the hole.
Service and Maintenance
Direct-drive hub motors can be run for many years with no need for any scheduled maintenance. Frequent exposure to salty conditions can cause corrosion/pitting of aluminum metal over time, but this does not affect your motor’s performance. If the motor does need to be opened up for service (e.g. ball bearing replacement, torn cable repair), the motor must be unlaced from the rim first. A gear puller is handy but not required. See Grin’s disassembly video for further details.
Additional Points
Wheel Lacing
The All-Axle motor uses 32 paired spoke holes, which results in the spokes having a tangential angle even in a 0 cross ‘radial’ lacing pattern. There is no need to cross the spokes with this hub.
Disc Caliper Clearance
Some hydraulic disc calipers are especially wide and may not fit between the rotor and the motor’s side plate. This is generally not an issue with these fat hubs as the disc spacers produce either a 20mm or 25mm gap that fits most hydraulic calipers on the market. If the caliper just slightly scrapes the plate an additional 1mm shim will do the trick. Larger interference requires changing to a different caliper model.
Temperature Limits and Thermal Rollback
The temperature required to burn the enamel off the motor windings and cause permanent damage is very high, over 180°C, but allowing the motor to get close to this value is not recommended as the efficiency and performance plummet well before then. It is best to keep the motor core under 110-120°C, which provides significant headroom from actual damage and ensures that the outside shell of the motor is not uncomfortably hot.
To automatically scale back power as the motor heats up, the controller system must respond to the motor thermistor which is a 10K NTC with a 3450 Beta constant. The table below shows the expected thermistor resistance at different temperatures
Table 4: Thermistor Resistance Table.
| Temperature | NTC Resistance | Voltage with 5K Pullup |
| 0 C | 28.9 kOhm | 4.26 V |
| 25 C | 10.0 kOhm | 3.33 V |
| 50 C | 4.08 kOhm | 2.25V |
| 75 C | 1.90 kOhm | 1.37 V |
| 100 C | 1.13 kOhm | 0.82 V |
| 125 C | 0.70 kOhm | 0.49 V |
Regenerative Braking
Direct drive motors can regeneratively brake extremely well and can produce the same braking force as acceleration force. Our integrated torque arm safely handles the alternating back-and-forth torque on the axle. Regen can greatly reduce the wear rate of your mechanical brake pads and can take over 90% of braking duties. We highly recommend taking advantage of this feature and adding regen control to your system. The supported regen control options for Grin’s three kit styles are summarized in the table below.
Table 5: Regen Brake Control Modes with Grin Kits.
| Regen Mode | Barebones Kit | Super hardness Kit | CA3 Kit |
| Digital Brake Lever | Supported | Supported | Supported |
| Digital Lever +Throttle | No | Supported | Supported |
| Analog Lever | No | Supported | No* |
| Bidirectional Throttle | No | Supported | No* |
| Backward Pedal | No | No | Supported |
| Speed limit | No | No | Supported |
| Assist Buttons | No | No | Supported |
Support is anticipated in future firmware releases.
Information on configuring the regen behavior is supplied by the motor controller and/or Cycle Analyst.
Anti-Theft Quick Release
Many anti-theft quick-release skewers are available on the market requiring a special tool to remove the hub. For those concerned about motor security, we recommend visiting your local bike store or searching online for anti-theft
skewers compatible with your bike frame.
Single Side Mounting
The All-Axle motor is also unique in that it can be mounted to single-sided spindles as commonly found in tadpole trikes, trailers, and quad bicycles. To support this application a special single-side adapter is offered that acts as a torque arm on the disc side of the motor, so that the cable, disc rotor, and torque arm are all on the same side.
Details on single-side installation are covered in a different installation manual.
Specifications
Electrical – Pinout
Electrical – Motor
| Winding | 4T (Standard) | 5T (Slow) |
| Grin SKU | M-AA4504 | M-AA4505 |
| Motor Kv | 9 rpm/V | 7.2 rpm/V |
| Motor Ki (Inverse of Kv) | 0.79 Nm/A | 0.95 Nm/A |
| Resistance (Phase to Phase) | 102 mΩ | 155 mΩ |
| Inductance (Phase to Phase) | 240 uH | 330 uH |
| Maximum Torque* | 120 Nm for up to 1 minute | |
| Continuous Torque to 110C** | 40 Nm standard, 60 Nm with Statorade | |
| Motor Hystersis Drag | 1.0 – 1.2 Nm Typ. | |
| Motor Eddie Current Drag | 0.0008 Nm/rpm | |
| Rated Power (EU/UK/Au/NZ) | 250Watts (70 rpm, no statorade) | |
| Rated Power (Canada) | 500 Watts (120 rpm, no statorade) | |
| Rated Power (USA) | 750 Watts (180 rpm, no statorade) | |
| Motor Hall Power | 5V-12V DC | |
| Hall Signal Level | Open Collector, pull-up required on controller | |
| Hall Timing | 120 degree, 8 degree offset | |
| Thermistor | 10K NTC. 3450 Beta. Ground Referenced | |
Mechanical
| Spoke Flange Diameter | 214 mm |
| Spoke Flange Spacing | 67 mm |
| Spoke Size Compatibility | 13g (2.0 mm) or 14g (1.8 mm) |
| Spoke Holes | 32, with 21 mm spacing between paired holes |
| Dishing Offset | 6 mm |
| Motor Diameter | 226 mm (flange), 212 mm (rotor) |
| Motor Width | 72.5mm |
| Weight (motor only) | 5.95 kg |
| Cable Length | 260 mm to end of connector |
CONTACT INFORMATION
- Grin Technologies Ltd
- Vancouver, BC, Canada
- ph: 604-569-0902
- email: info@ebikes.ca
- web: www.ebikes.ca
Documents / Resources
 |
GRIN TECHNOLOGIES Fat Front All-Axl Motor Build [pdf] Owner's Manual Fat Front All-Axl Motor Build, Fat Front All-Axl, Motor Build, Build |
