Hi, in this post I’ll be releasing some coaxial swerve modules I color-coded using premade COTS modules and Autodesk Inventor. I’ll explain how the MK4, MK4i, and MAXSwerve modules work mechanically.
Firstly, I’ll explain what coaxial swerve is. For those who don’t know, coaxial swerve drive is a common form of swerve in FRC and uses two motors. It allows each wheel to rotate in an independent direction, and spin at an independent speed. Because of this, swerve drivetrains have an unmatched level of maneuverability, but at the cost of added complexity. One motor determines the direction the wheel is facing, while the other determines the speed at which the wheel spins. Swerve usually uses a modular design, meaning each wheel (there are usually two to four wheels used) uses the same mechanical and electrical design. Due to this approach, if one module is damaged or needs to be replaced, it can simply be taken off of the frame and replaced (assuming they’re mounted using removeable fasteners).
Now, I’ll explain my color-coding conventions. Silver or light gray objects are bearings and are used to better represent how the mechanisms work as the supporting structure has been removed for this demonstration. Red objects are the components which allow the drive motor to be able to spin the wheel. Blue objects are similar to the red ones, but they indicate all of the objects used to allow the turn motor to determine the direction the wheel is facing. The Bague objects indicate the encoder used and all of the components used by that encoder.
All three of these module designs use an encoder to measure the direction of the wheel. If you don’t know what an encoder is, it’s basically a sensor which measures the angle/position of something and can therefore be used to measure not only the angle, but RPM as well.
Firstly, here’s the MK4:
MK4 Swerve Module – Swerve Drive Specialties
As you can see, there is one system used to control the direction of the wheel, and one to determine the speed.
The left motor is the drive motor (the motor that determines the speed of the wheel), and the motor on the right is the turn motor (the motor which controls the direction of the wheel).
The turn motor starts with a pinion gear (the spur gear on the output shaft of the motor), which rotates a spur gear. The spur gear has a shaft which leads downwards. At the end of shaft is a pulley. The pulley then spins a timing belt (the teal object) which rotates the large pulley in the center of the module. Two legs protrude from that central pulley, and the wheel and its axle rest on these two legs using ball bearings. You can think of the pulley, legs, and wheels, as the thing the turn motor is trying to rotate.
For the drive motor, a pinion gear is used to spin another spur gear which is located in the center of the module. That spur gear is in the center so that when the wheel and central pulley rotate, this spur gear is still in the center of the pulley and not at a different angle to the wheel. The spur gear under it is part of this spur gear, and they’re created as one singular piece or object. What this means is, when the higher spur gear rotates, so does the lower one. When it rotates, it spins the spur gear next to it, which has a shaft leading down to a bevel gear. This gear is used so that it can always stay at the same position on the pulley and more importantly, at the same angle as the wheel, while maintaining a mesh with the spur gear in the center of the module. The bevel gear spins the ring gear or rack which is set on the wheel, causing the wheel to finally spin.
There is also an encoder located in the center of the module. Utilizing bearings, its shaft passes through the red spur gear without interacting with it, and measures the blue pulley underneath. By doing this, it can tell the computer what position/direction the wheel is facing at any given time.
Next, the MK4i:
MK4i Swerve Module – Swerve Drive Specialties
Both systems begin the same: with a pinion and spur gear. The motor on the left is the drive motor, and on the right is the turn motor.
The spur gear which interacts with the pinion on the drive motor turns the red spur gear located in the center of the module. From there, it’s the same as the MK4 in that the spur gear beneath it is actually part of the higher spur gear. It then rotates another spur gear, which has a shaft leading downwards through the pulley, which has a bevel gear at the end that spins the bevel ring gear or rack.
The turn motor rotates a spur gear using its pinion gear, and the spur gear has a shaft leading downwards. The shaft has a pulley at the end, which rotates the central blue pulley using a timing belt. Like the previous module (the MK4), it rotates the wheel using the same design.
An encoder is used on this module as well, and functions exactly the same as the MK4.
Finally, the MAXSwerve:
MAXSwerve - ION BUILD SYSTEM (revrobotics.com)
This module is a little different, but its core mechanisms are very similar.
Firstly, it uses two different sized motors because the turn motor doesn’t need to be as powerful as the drive motor. All it really needs is enough torque to turn the wheel, and the ability to do it fast enough.
The smaller motor on the right is the turn motor, and it goes through some gear boxes before rotating a spur gear. The gear boxes are used to change the gear ratio/output torque. The output shaft from the gear boxes then rotates the larger blue spur gear in the center of the module. This gear acts the same as the pulleys in the previous modules and has protruding legs which support the wheel.
The drive motor is on the left. It uses a pinion gear to turn a spur gear, which has a shaft running through the central blue gear. At the end of the shaft is a bevel gear. Like the previous modules, this bevel gear spins the wheel by rotating the bevel ring gear or rack which is set on the wheel.
This module uses an encoder like the other two. The encoder passes through the red spur gear using a bearing and measures the blue gears position. It works similarly to the encoders from the previous modules that both ran through a centered red spur gear as well.
Anyways, this was just meant to be a guide for those new to swerve. I’m still learning and created these myself so that I could expand my knowledge on swerve. If I got anything wrong, please let me know, and the same goes for questions as well.
