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Picture of Control K'nex With a Mobile Phone

In this instructable, you will learn how to make a K'nex Bobble Car. It is so named because the code you will be using for this project is open source software I developed called "Bobble" which runs on an Arduino board and responds to easy one letter commands to control one motor, one servo, and one analog input from an attached sensor. This instructable can be very easily generalized to other K'nex (and even non-K'nex) projects.

We will be using an Adafruit nRF52832 Bluefruit LE board which combines an Arduino processor and Bluetooth LE (Low Energy) driver. Using a Bluetooth LE connection, you will be controlling the bobble with an Android phone application that was written using App Inventor 2 which is a visual programming tool that makes application development super easy. Although I will provide you a link to directly load the application file on to your Android device, I also encourage you to open the source code for the project under App Inventor 2 so that you can see how the simple application works and modify it as desired. The code was designed to be easily understood and modified.

Step 1: Required Parts for This Project

Picture of Required Parts for This Project

Besides the K'nex parts shown here, you will also need the following parts:

1 Modified K'nex motor (see link2_thepast's excellent instructable Arduino + K'nex Motor)

1 Half-size solderless breadboard (400 Point)

1 Modified 9g micro servo (instructions in this instructable for adding K'nex parts)

1 Adafruit Feather nRF52 Bluefruit LE - nRF52832

1 L293DNE 4 channel motor driver

1 Silicon NPN Phototransistor

1 10K ohm resistor

1 (optional) 3-pin male to male header [just snap apart a larger header]

1 3x AA Battery Holder (with switch) and 3 AA batteries


NOTE: For the modified K'nex motor, you will only need the two leads connected to the motor. The power and ground leads will be unnecessary for our purposes since we will be using an external battery case.

If you would rather just bypass all of these steps and just purchase an assembled K'nex Bobble Car for $68, just contact me and we can set you up with one today.

Mister Gears2 months ago
do you know how much amperage the motor absorb ? I need it for my project

reachandteach (author)  Mister Gears2 months ago
Unfortunately, don't know the complete answer to that question. There is not a lot of info out there about the various motors. The best instructable on the subject is https://www.instructables.com/id/A-Complete-Guide-to-Knex-Motors/ but won't cover that. What I can say is that I'm using a K'nex enclosed battery motor and that they are normally powered by 3V (2 AA batteries). I've operated the motor externally on various projects with up to 6V (typically 5V) and have not experienced any overheating or damage under load. I would probably use a current limiting resistor if I was going much above 6V or use a separate supply for the motor. I'm using a L293DNE to drive the motor which has protection diodes built-in and does offer connection for separate supply voltages for the motor logic controls and the motor outputs.
jessyratfink5 months ago
This is great! Always like to see K'nex used this way :)
reachandteach (author)  jessyratfink5 months ago
Thank you!