550 vs 775 Brushed DC Motors
Motor Size Comparison (550 stock, 775 Redline, 887 Johnson Electric, 895 Um… No idea who makes it)
Introduction:
Most ride on toys come equipped with 550 size motors (For more details on the stock motors reference the Motor Guide). This article is a continuation of the original Ride on Toy Motor Guide.
Executive Summary:
We have tested just about every motor that made sense to test in a variety of ride on toys over the last year, we have found the best value to be Vexpro or AndyMark 775 motors for most cars.
For those seeking the highest performance, we found the Johnson Electric 887 motors to perform the best (We aren’t racers, our kids just have fun in the back yard) and for the best low end torque for crawling are these 895’s (20K RPM @ 24V), we have had some failures but they seem reliable enough.
Issues you will encounter:
When upgrading from 550’s to 775’s (or larger) the gear box must be able to handle the motor (power and size), larger motors have more torque which can cause gear box failures (we recommend adding a variable speed controller where the throttle ramp up and brake ramp up times are configurable). Power wheels 7R gear box (the most common gear box in power wheels brand toys) can accept all 775 motors we have tested by simply drilling out one pre-molded hole. Every other brand that came with a 550 size motor could not easily fit a 775 (or larger motor) without an adapter.
The Johnson Electric 887 motors are easily adapted to fit the 7R gear box with a simple adapter.
To fit larger motors into another gearbox style, you will have to either modify the gear box are design an adapter of some kind.
Why go bigger?
The larger the motor, the more torque the motor is capable of producing (typically), for the example motors shown in the figure above, each time the motor size increases, the rated RPM decreases but the power increases. Remember these equations?
Power (Watts) = Current (A) X Voltage (V)
Horsepower = 745.7 Watts (This is mechanical power, brushed DC motors are at best 80% efficient at converting electrical power into mechanical power)
Horsepower = (Torque X RPM) / 5252
We can see using the above equations that torque is increasing quickly with size, overall power is increasing, but, we are losing RPM at a given input voltage. What does this mean for increasing speed? The larger motors can handle higher voltage (24V can be achieved reliably and some people have reliably run 36V batteries, we haven’t had good luck with two kids and hills at 36V). We can also change the gear ratio by using a larger pinion gear to increase the final output speed. Typically stock gear boxes cannot handle different size pinion gears without modification.
Why choose an 887 or 895 motor? These motors have much better cooling and offer significantly higher torque when operated within their rated specifications. If you can achieve the desired performance and operate within the motor manufactures specifications, you will have a lot more reliable toy that requires less time fixing.
Increasing the input voltage increases the speed:
Higher voltage results in higher current, Power = Voltage x Current
Higher Current produces a stronger magnetic field pushing armature away from the magnets faster.
Above is a depiction of how the voltage gets delivered to the motor windings through brushes. An electromagnet has been produced and it is allowed to rotate and push away from the permanent magnets within the motor housing.