The drive system consists of everything that makes the scooter move. This includes motors, wheels, and any gears, belts, or chains connecting everything.
First let's talk about the motors… There's a huge variety to choose from out there in different shapes, sizes, speeds, and power requirements. The two main types you should consider are brushed and brushless motors:
- Brushed motors are usually cheaper and easier to come by, but are not as efficient or powerful as brushless motors. Wheelchair and scooter motors are usually brushed.
- Brushless motors are fast, powerful, and smooth running, but rarely have any kind of gearing and can be harder to control at low speeds. When choosing a brushless motor you also need to consider whether to get a sensored or sensorless motor. Sensorless brushless motors are cheaper, but don't provide as great a level of control as a sensored motor. This choice will also affect your choice of motor controller later on. Most hub motors (such as those used by electric bicycles) are brushless, though they can be found in a wide variety of other shapes/sizes.
Once you decide what kind of motor to use it's time to actually find one. EBay is a fantastic source of new and used motors for wheelchairs, bikes, and scooters; though some searching around on the internet can lead to other sources. But some things to consider before buying your motors are...
- Does it have a gearbox? Almost any motor you choose will need some kind of gearing to increase its torque, though hub motors can probably get by without. This can be achieved with a gearbox, chain, or a belt and pulley. If a motor doesn't have any of these, you'll probably need to add them.
- How is it mounted? Many motors already have a method of attaching them to a chassis, but will it work for your design? The ideal mount will let you bolt a motor/gearbox directly to your chassis, though any motor <5-6" in diameter can likely be strapped to a chassis using hose clamps if no other simple solution can be found.
- Is it oriented a certain way? Many motors that come with a gearbox, especially those on wheelchairs, are designed to be mounted in a certain orientation. Consider whether their designed orientation will work for you. Or, if not, can they be oriented in some way that will work for you, even if it's not the orientation they were designed for
- Is there likely to be any play or slop between the motor and wheel? This is possibly the most important factor in selecting a geared motor or designing a belt/chain drive. Any movement the wheels can make without turning the motors is tilt your scooter can't compensate for properly when changing direction or balancing in place. A couple to few degrees of play is ok, though it will be noticeable, but it should always be kept to a minimum. Bicycle hub motors are the ideal solution to this problem, since the motor and wheel are one piece, but I have yet to try such a setup so I can't promise it will work.
Next up is deciding on wheels and how you want to drive them; though if your chosen motors already have wheels, you're probably best off using them as it will save you a lot of time and effort. But if not, here are some things to consider...
- How tall do you want your scooter to be? The base of your scooter (the part you stand on) will likely be about as high off the ground as the radius of your chosen wheels. And the higher above the ground your base is, the more potentially dangerous and scary your scooter will be.
- How fast do you want to go vs. how much control do you want? Larger wheels will allow you to go faster, but smaller wheels will give you a higher degree of control.
- How will you attach them to your motors? Many wheels you can buy are designed purely to rotate freely, not be driven by a motor, meaning they need a custom mounting hub. Making a mounting hub for a wheel can be very difficult and also needs to be centered nearly perfectly when attached to the wheel. It's a lot easier to find a wheel that already has some method of attaching it to a gearbox or pulley/sprocket.
And lastly, you need to determine how power will get from your motors to your wheels. The easiest method is simply to use motors with a gearbox and simply attaching the wheel to the gearbox output or using hub motors, which need no gearing. But for motors that don't have a gearbox or the strength to directly drive the wheels you'll likely need to attach the wheel and motor via a belt or bicycle chain. I can't recommend one over the other as I've only ever used motors with an attached gearbox.
And now that we've got the drive system figured out, let's move on to the Power System.