This is a follow up post to Stick Shift Lego Monster Truck

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Last Month Hackaday had a post for "Converting a Robotic Motor For Lego Blocks",

and I happen to be building a Lego Monster Truck and I need a good way to power steering my vehicle. So I followed the instructions in the above post. But it turns out it requires more hand craft skill than I thought, and I don't have the 4.8 mm drill bit either, thanks to the imperial systems (The closest one I have is 3/16 inch, but I couldn't make it to work).

Fortunately, since I only control the gear box on one side, I found another way to hack:

1) Get a DC 3V-6V Dual Axis Gear Motor. The motor can be obtain from banggood.com, or AliExpress for less than $1

2) Use a 5/64 inch drill bit to drill a hole on one end of a Lego axle, as illustrated below. For the Lego axle, find the end that has a small dip, which is easy to position your drill bit.

3) The DC motor has two axle heads, with one on each side. One of the axle head is tied to a gear inside the yellow gearbox, so there is not much you can do unless you open the yellow gear box. But the other axle head can be pulled out without opening the yellow gear box. And that one is attached to a metal axle with a seesaw head. Plug the reworked Lego axle from (2) into the metal axle, and you get yourself something that can be used to drive the Lego gear box

4) Use PWM to control the motor, which will drive the Lego gear box (shown below before motor is mounted). Now my Lego monster truck can make turns left and right!

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PS: ways to mount the dollar motor

There are many ways to mount the motor onto the Lego bricks. I simply use cable ties to attach the motor firmly to the Lego gearbox.
But you can also stick a 2 x 4 plates (with holes in the middle) to the motor.

Or you can use a Lego compatible DC motor support from the following

(The motor in the following is NOT the same as the one I hacked)
https://www.amazon.com/gp/product/B072HRR8W4/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1