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I want my young kids to be able to have adventures and robot battles with the Atari joystick controlled robots. To make the collisions more spectacular and to allow them to participate in building the robots, I decided to make the robot frame out of Lego bricks.
A Lego motor with its cable modified with a Molex KK connector to fit 0.1 headers.
Even though the robot controller board is not a Lego product, it is possible to attach Lego motors to it. Cut a Lego motor cable in half and strip the ends of the wires to create two Lego-to-bare-wire cables. You can either solder the wires to a breadboard or you can crimp connectors to make them compatible with standard 0.1″ headers.
But, there are some concerns with using Lego motors:
An alternative is to use an off-the-shelf motor and adapt it to Lego parts.
A pair of Solarbotics GM7 gearmotors attached to Lego bricks to make a robot frame.
The GM7 gearmotors from Solarbotics are less expensive, readily available, and provide an appropriate speed for this robot. They can be mounted to Lego bricks by using #2-56 screws and washers. The washers spread the load more evenly across the plastic and prevent damage as the nuts are tightened.
You can modify the GM7 motor for screw mounting without needing a drill press or mill.
Modifying a GM7 motor for machine screw mounting by removing the existing screws and drilling through with a 3/32 drill.
First, remove the two factory installed screws. Don’t worry! The plastic case will remain in one piece because the shell is snapped together.
Install a 3/32 inch diameter drill bit into a power drill. A 3/32 is the correct size for a clearance hole for #2-56 machine screws.
Using the existing screw holes as guides, insert the drill into the holes and drill out through the other side. Avoid drilling into your hand when the drill breaks through!
Interestingly enough, the original screws still fit if you change your mind and decide to mount the gearmotor using a different method later on.
A 1-inch long #2-56 screw is necessary to secure the gearmotor against a 1 LU (Lego Unit) width Technic beam, with spare room for washers and a nut. For about $5, you can purchase 100 stainless-steel flat head screws (#91771A140 from McMaster-Carr) or pan head screws (#91772A086).
Flat head screws fit flush with the gearmotor case, but pan head screws stick out somewhat.
The flat head screws are nice and flush, but the remaining 96 screws won’t be as useful for other projects. The pan head screws are more versatile for other projects, but stick out a bit on the motor. A flush screw head probably isn’t necessary, but it depends on what kind of tire you use.
Most Lego wheel hubs are asymmetrical, meaning the distance between the wheel and motor depends on which side of the wheel faces inward. This photograph shows the same wheel pressed on as far as possible, but installed in the opposite orientation.
I chose to make Lego couplers for my motors. As such, the robots have access to a wide selection of Lego wheels. If you find that the wheel rubs against the screwhead or the side of the robot, you can try a different wheel or (sometimes) flip the wheel around.
If you don’t want to make a Lego coupler, you could probably drill a 2.1 mm hole into a plastic object and force fit it onto the GM7’s splined axle. Or, I suppose you could fill the center of an incompatible wheel with epoxy, and then drill a 2.1 mm hole, and force fit.
The backside of the Solarbotics motor has raised areas that necessitate using a washer to space the Lego Technic beams far enough away to remain straight.
Because the mounting side of the gearmotor is not completely flat, you'll need to use washers between the motors and the Lego bricks so that they will stay flat when tensioned by the screws and nuts. I chose thin stainless steel washers (#92141A005 from McMaster-Carr) that generally can be used for either #2-56 or #4-40 screws. Plain steel washers are less expensive, but can rust.
Let’s see the completed robot in action...