Motorized Bobby-Car (1600W)




Introduction: Motorized Bobby-Car (1600W)

About: I am a student of mechanical engineering and like to work on small projects.

Someday I've got the idea of getting a Bobby-Car motorized. In the first
place it seems kind of idiotic to waste so much money on something you can't even drive on a public road. On the other hand, it appears like a challenge for myself. So, I decided to take the challenge.

This is my first Instructable, so please give me feedback and I can improve my future Instructables. Furthermore, this won’t be a step by step instruction that means there won’t be any measurements or some other specific details.


- different types of metal tubes and sheets

- electric motor

- motor controller

- gas throttle

- set of brakes (lever, disk, blocks, wire)

- batteries

- wheels (cross skating)

- steering bar

- bearings

- motor chain + gears

- bolts

- charger cable

- paint

- last but not least a Bobby-Car

Step 1: Planning Is the Main Work

The main limitation of this project is the Bobby-Car itself. The only original part I am using is the chassis itself. The wheels or the axis are way too fragile. So, the limitation is the space inside the chassis. Based on that I measured the inside of the body, which isn't a clear shape. The planning is the first step, but it is part of the complete project, because of the complex body of the bobby Car.

For the most parts I used to make 1 on 1 scaled drawings. These drawings helped me to figure out where I've to place the components inside.

Step 2: Building the Under Body

The materials I used for the Body:

- metal profiles

- rod electrodes

- primer

- black paint

The body is based on smaller square tubes which I welded together. This was done with an old electrode welder. It was my first time to welding something together, so be indulgent with the results.

The body is split into two parts, the upper and under body. The under body is made out of tubes that are welded together. So, I don't calculate any loads or forces that would affect the structure, therefore I made it more solid than it has to be. With some grinding I take off the sharp edges. After that step I take on some primer and the chosen colour, which was black in my case. The final shape of the body is a process which take the many time, because it was based on the following steps and parts.

The upper body is the part between the internals and the original plastic chassis. This is made out of aluminium tubes, that are screwed together. For me it was simpler to make since my welding skills aren't the best. For a better view I made myself some scaled drawings.

Step 3: Building the Steering

The materials I used for the steering:

- two individual steel axis

- metal tubes

- bolts

- screw nuts

- plain bearing (Igus)

- threaded rod

- wheels (cross skating)

- bearings

- self-securing nuts

As I said my welding skills need some lessons, so maybe train a little bit more than I did.

For the steering I decided to use a knuckle joint steering. I welded the individual axis onto a tube. On the axis the wheels are joint and secured with a self-securing nut. Therefore, I've cut a threat on the axle. The tube use to be the rotary point and is fixed with a bolt in place. It can free spin on plain bearings which are fitted I the top and the bottom of the tube. An additional steering knuckle determines the steering angle. The wheels turn on the axis with bearings freely. In the middle of the steering is a threaded rod fitted into a nut, which has also a tight welded on. The steering knuckle are connected with a ball joint. On top of the threaded rod is the handle bar connected.

Step 4: Building the Power Transmission and the Brake

The parts I used:

- electric motor

- motor controller

- gas throttle

- charging port

- bearings

- costume made axis

- self-securing nuts

The power from the electric motor is transmitted with a drive chain. With a transmission of 62:11 the motor spins nearly 6 times faster than the rear wheel axle. This and the 1.6 kW motor allow the bobby car to reach speeds up to 50 km/h (theoretical, never measured it). The rear wheel axle contains tree parts. One main part, that connect both wheels and two "sleeves". On one sleeve the gear wheel, that take the power from the motor, is screwed on. A brake disk is connected to the other sleeve. The sleeves additional contains the back wheels. The axis is individual made by a friend of mine. At the end of the main part are self-securing nuts screwed on to hold the sleeves with the wheels in place.

Step 5: Installing the Electric Motor

The electronics I am using:

- a 1600W 48V brushless motor

- a 1600W 48V speed controller

- gas throttle with key switch

- charging pole port

- charger

The motor is bolted on the under body. Therefore, an additional piece of metal is used to secure the motor against twisting. A slotted hole is used for the tension of the chain, so the distance between the gears can be adjusted. I bought the electric motor, the motor controller and the gas throttle together as a bundle, as a result I don't have to care about complicate wiring.

The batteries take place in the front of the lower body. I've glued some rubber band onto the metal to protect the batteries from small shocks. Above the motor controller is installed.

Step 6: Building the Batterie Pack

For the batterie pack I am using:

- four 12V 9Ah batteries (motorcycle batteries, because the are smaller than car batteries)

- rubber foil

- cable lug

- duct tape

- wire

First I bundle the batteries in two packs. I've taped them together with duct tape. Then I glued an sheet of rubber on the upside to protect the connections of the batteries of creating an short circuit. This is necessary because the batteries are packed close together, as you can see in last picture. The batteries are connected with some cables in a series circuit to create 48V. With some pressure of the upper body the batteries are fixed in place with the rubber as protecting layer.

Step 7: Building the Upper Body and Preparing the Shell

The upper body supports the outer shell of the Bobby-Car, because the
average person would be too heavy for the plastic shell itself. The form of the upper body is based on the shape of the internals. Mainly based on the motor, the batteries and the motor controller. Because the is no clear shape of the body of the Bobby-Car it is difficult to build an exact contour. Therefore, I used bolted aluminium profile construction. It is lightweight and kind of adjustable. The upper body is connected at the front and the back of the Bobby-Car, additionally it lay on the shell of the motor for additional support. The bolted construction allows an easy disassembly.

I've glued some cut plywood into the shell of the Bobby-Car to strengthen the structure. At the back there are some deepening in the shell, these ones I've filled with hot glue for additional stability. At the first try the huge amount of hot glue melted the plastic shell of the Bobby-Car. Therefore, I placed some water underneath the shell to absorb the heat. Between the shell and the upper body there is an huge gap at the back of the car. Therefore I've glued an piece of wood on the shell to bypass this gap. I've had to make sure that the wood block is underneath the sitting position of the driver to support the structure.

Well it doesn't look good, but it can handle the force which is the more important task.

Step 8: The Assembly

The final step is the assembly of the parts. In the following part I will
describe important notes of each step.

The assembly starts with the steering. Therefore, the knuckle joint steering is bolted onto (between) the frame. Make sure to use the right tightening torque, so the tubes of the knuckle joint can’t slide vertical, but spins freely. Then adjust the steering angle with the threaded rods at the front to get both wheels parallel to each other. The threaded rod is counted with a nut to secure the rod against losing. Because the last thing you want is to lose the control about the steering at higher speeds. Another nut secures the rod from getting pulled out of the steering.

In the following the rear axis is assembled. The parts of the axis are assembled as shown in the chapter. Because the power transmission is realized with a frictionally engaged shaft-hub-connections make sure to use a high tightening torque.

With the rear axis in place the motor can be mounted. With the slotted hole at the frame the chain can be stretched.

In the following the brake can be mounted. Make sure the brake shoes don't scratch on the brake disk. Therefore, the exact position can be modified. The battery pack is mounted between the lower and upper frame. The friction between this part is enough to fix the pack in the right place.

For the wiring take a look at your circuit diagram. The motor controller sits on top of the upper body. Make sure that you cut your cables a short length, because otherwise you can get problems with the spinning parts. (My wiring isn't a good example)

And finally, the shell of the bobby car is mounted (therefore, you have to mount the steering handle after you mounted the frame). The shell is bolted at the front and the back to the lower body.

Step 9: Final Test

Before riding make sure to wear some sort of protection. I hope you liked the instruction and if you have some question feel free to ask.

I would be happy if you would vote for my project in the competition "Motor Vehicle Contest".

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    2 years ago

    Very impressive build! : )