# How to design N:P Lego Technic MOC Gear Ratios using two Lego Differentials

Here I present a tutorial on methods for designing N:P Lego Technic MOC Gear ratios where N and P are prime using two differentials. Several differential topologies are presented and one cross connected topology is mathematically analysed and the relationship equation between the input and output derived. Using this equation and the computer solutions for the 1:N gear ratio designs from Part 2 of this series, an example is worked through to create a 313 to 421 gear ratio. This gear ratio design is much more efficient than simply connecting an N:1 and 1:P design in series.

# More to explore

## How to use a Lego Technic differential for creating prime gear ratios for MOCs. Part 1

Here I discuss techniques for creating prime number gear ratios such as 17:1, 19:1, 23:1, and 53:1 using a Lego Technic differential. Learn the mathematical relationship between the gear to create your own MOC desired ratios. Use this lego differential tutorial to design your own lego gear ratios...read more

## New Flat 12/20 Gear Friction

The Lego Technic set 42140 App-Controlled Transformation Vehicle introduces two new gears - a flat version of the 12 tooth bevel gear and a flat version of the 20 tooth bevel gear. These gears are designed to have less friction.

In this video I measure the difference in gearing efficiency...read more

### Gearing Ratio Calculator Tool Help

## Lego Technic Powered Up Tutorial 2 - Speed Control

This is my second Lego Technic Powered Up Tutorial that focusses on Lego Technic motor speed control using the Powered Up hub and Powered Up programming interface. The Lego Powered Up App is run on a Samsung Android tablet. I demonstrate how to set and control the power level applied to a motor.<...read more

## Measuring Gearbox Efficiency

This video describes a method for measuring the efficiency of a gearbox using the Lego Technic Powered Up hub. Gearbox efficiency is defined as the ratio of the output power to the input power and here I show how to measure each of these values to allow you to calculate the overall efficiency.read more

## Lego Technic Gearing Ratio Tool Update

This video presents updates to the Technic Brick Power Lego Technic Gearing Ratio Calculator tool specifically on underconstrained differential systems. These are systems in which the differentials are not fully constrained and therefore have 1 or more degrees of freedom within them.

The ...read more

## Lego Technic Gearing Ratio Calculator Tool

Here I present my new Lego Technic Gearing Ratio Calculator tool. This tool allows you to upload your Lego Technic .ldr (Lego Draw) file and it will simulate the gearing system and visualize it as well as showing the gearing ratios relative to the input component.

The tool can be accessed...read more

## Lego Technic Applied Gearbox Theory Improved

This Lego Technic video demonstrates an improved design of a Lego technic 2 speed automatic gearbox based on a theoretical approach. Typically a Lego automatic gearbox consists of two stages namely a gear selector and a torque detector. In this video, both of these components are improved upon.read more

## Lego Technic Gearbox Theory Applied - how to apply theory to help design 2 speed automatic gearboxes

This video applies lego technic gearbox, torque, and gearing ratio theory to design a prototype lego 2 speed automatic gearbox. First I describe the main components of an automatic gearbox, namely a gearing ratio selector and a torque detector. The ideal gear switch over torque point is described...read more

## Lego Technic Optimal Gear Switching Ratios

This video presents the relationship between lego technic motor torque and speed and shows there is an peak power for each electric motor.

The peak power is calculated and a formula presented relating the power operating point as a percentage of peak power. From this an operational power ...read more