Sourcing the parts
Here is a fun little electric trike for your young DIY enthusiasts that can be built in a single evening from a pair of children’s bicycles, a few bits of scrap tubing and an old stand up electric scooter. Actually, this project is so simple that you can make it out of practically any battery powered DC motor and any scrap bicycle parts you may have lying around the shop. Since speed is certainly not the goal here, even an old cordless drill will make a fine power source for this vehicle, allowing your kids to run around the yard for as long as the batteries hold out.
You can purchase one of those small plastic electric kids cars at just about any toy store, but the all plastic construction and low wattage motor may not keep up with the kids demanding driving habits. If your yard or park is not perfectly smooth and hill free, the department store vehicle may wear out in a hurry, or simply fail to traverse the terrain. By using a pair of kids’ bikes for the wheels and forks, this electric trike becomes a high quality vehicle, capable of driving on gravel, up hills, through the mud, and even on the grass.
Since kids’ bikes come in many sizes, with wheels measuring 10 inches, 12 inches, 14 inches, and 16 inches, you should not have any problem scrounging up the parts for this project by visiting the local dump or hitting the yard sales around the neighborhood. The parts are really not critical, but you will want the two front wheels and two front forks to match, at least for size and shape, since they will be placed side-by-side on the trike.
This photo shows the basic parts that will be needed in order to put together the kid’s trike. You will need three bicycle wheels (two of which should match), three front forks (two of which should match), one head tube and bearing set to match one of the front forks, and some type of DC motor that can power one of the wheels. I chose an old stand up electric scooter motor as the power source because it could be placed against one of the trike wheels to make the vehicle move, thus requiring no transmission, gears or chains. These little stand up scooters are also plentiful at yard sales and scrap piles, since it is often the frame that bends before the motor fails.
As shown here, you will need these components for the front of your trike – a front fork and matching head tube with all included bearing hardware. This head tube actually came from the electric scooter, and it just happened to fit the kids bicycle fork stem perfectly. With all of the bearing hardware installed, the fork will spin freely and without friction, which is a sure sign that all the hardware is properly matched. If you take your front forks and head tube from the same bicycle, then you will be certain that all hardware matches.
To make the kids trike, you need two wheels and forks for the rear and one front fork, wheel and head tube. For this reason, the two rear wheels and forks should match, and the front wheel can be whatever size you want. On my trike, I decided to use three matching wheels since they were easy to locate, and I also used a front fork that was slightly larger than the two at the rear. You will also notice that all the wheels are actually front wheels, since there is no drive chain needed you will not need a wheel with a sprocket attached. You could use a rear wheel if you cannot locate three front wheels, but a little force will be needed in order to widen the fork legs to take the larger diameter rear hub and axle.
Most cheap stand up electric scooters have a 100-300 watt motor connected to a small rubber wheel, like the wheel you would find on a road skate. These motors will typically move the scooter at a speed of 15 to 20 miles per hour when using a good 24 volt power source. For use on a kid’s trike, I decided to use only one large 12 volt battery, reducing the top speed to about 10 miles per hour, but extending the run time by many hours.
Since the motor already turns the small rubber drive wheel, all you need to do is let it rub against one of the trike wheels, and you will have a simple friction drive transmission system. Whatever speed the scooter would be capable of will be the top sped of your trike, since there is no gear reduction. As long as the scooter drive wheel is turning the bicycle wheel by contact at the edge of each wheel, there is a 1:1 gear ratio, so wheel size makes absolutely no difference to the final speed of the vehicle.
Building the frame
Cut the stem from each of the rear forks just above the crown as shown here, being careful not to nick the top of the fork leg tubing. The cut area will be the point at which you will attach your new frame tubing, as this is the strongest area of the fork. If for some reason your forks are not exactly the same, try to cut each stem so that the distance from the axle to the cut area will match on both forks.
Since I am building this kid’s trike from parts I already had around the garage, I simply placed the two rear forks on the ground and found a pair of 1 inch diameter square tubes that would create the triangular frame as shown here. I think the square tubing came from an old table I hacked up, but since the trike is only going to hold the weight of a child, you don’t need to use heavy tubing.
As for the size of the frame, simply have your young pilot sit on a chair, and make some basic measurements of how much room they will need in order to sit comfortably between three wheels. I went for a wheelbase about the same as the original bicycle, and a width of about the same as the wheelbase, creating an equilateral triangle footprint.
Part 2 in tomorrow’s blog.