For those of you in the know about vehicle suspension engineering, unsprung weight negatively affects the ride and comfort of a vehicle. What happens when you increase the weight of a wheel two- or -threefold is a drastic increase in th e unsprung weight of a vehicle, or weight that is not held up by a suspension. Until we make magic carbon nanotube superconductors en masse, motors are essentially chunks of steel and copper, both very heavy elements. Hub motors ar e inherently heavier and bulkier than driven wheels. I mean, read these few pointers which highlights some design tradeoffs and considerations involved in the use of hub motors! They are not perfect solutions to every drive problem, and some of the shortcomings are dictated by the laws of physics. Is a hub motor the right choice for your electric vehicle? Answer these few simple ques. It is stiffly mounted to the shaft (a nonrotating axle) which also seats the bearings for the rotor assembly. Internally, the stator is a specially shaped piece of laminated iron pieces (the stack) which holds windings (or coils) made of turns of magnet wire on its projections ( teeth). This whole rotating assembly is the r otor. The can (or casing) hold a circular arrangement of magnets (electrically called poles) and is supported on one or both ends by endcaps. Let's clear up some of the vocabulary and nomenclature immediately. I will assume some familiarity with basic electromagnetics concepts in order to explain the motor physics.īelow is an exploded parts diagram of a prototype motor that I am in the process of designing and building. The intention is not to design a motor that maintains above 95% efficiency across a thousand-RPM powerband, nor win the next electric flight competition, nor design a prime mover that will run at constant power for the next 10 years in an industrial process. The information is purposefully not academic in nature unless there is no way to avoid it. Many assumptions, shortcuts, and "R/C Hobby Industry Rules of Thumb and Hand Waves" will be used. This is intended as a basic primer on DC brushless hub motors.
The arrangement of this Instructable is designed for a read through first - because it relays theory and advice more than specific instructions on how to create one particular motor. Finally, I will briefly glean over ways to control your newfound source of motion. I will provide some thoughts and pointers about the mechanical construction of the motor itself and how to source major components. I will first exposit some of the details of brushless DC motor theory as applied to hub motors. Hence, I will attempt to show that a brushless DC permanent magnet hub motor is actually relatively easy to design and build for the hobbyist, resource access considerations aside. Until now, I have not had a single collective resource to point anyone towards, nor have I been confident enough to understand what I actually built to write about it for other hackers. The advent of my project RazEr, a stock Razor scooter with a custom built electric conversion, has raised many questions from amateur EV builder looking to construct their own brushless hub motors. They are also not as complex and mystical as one might think. Pure DC electric hub motors, in fact, were used in some of the first electric (and hybrid electric) cars. They're compact and modular, require no support of rotating axles from the parent vehicle, and can be designed around the vehicle to be propelled.
That is, they're great for EV hacking and conversion. In-wheel electric drive motors represent an effective method of providing propulsion to vehicles which otherwise were not designed to have driven wheels.