Monday, April 2, 2012

Building a Steering Drive

Steering is an essential component of building a Robot. What fun is a machine that can only go forwards and backwards? 

There are a lot of different ways to steer a robot, and one of the most common one is to build a rack and pinion steering drive. The steering drive is used by basically anything with a steering wheel, it's set up so that a gear on the end of the wheel (called a pinion) is meshed with a rack connected to the wheels. 

The rack is set up such that there are two degrees of motion, on either side of the set-up, and there's also a non-moving piece to give the wheels something to rotate around. Here's a good (non-lego) diagram of the system:

Now implementing the rack and pinion system into Lego form is tricky, but there are tons of unique solutions out there that I encourage you to take a look at. A quick google search of "Lego Steering Drive" will pull up some really cool results. 

In an effort to demonstrate on possible model for a Lego steering drive, I built this: 

The steering shaft is controlled by an independent motor, and by playing with the rack sizes, and wheel spacing, you can manipulate the turn radius as well. Building a solid chassis is important for steering drives, as they can quickly become heavy, and excessive moving parts can put stress on a robot. I locked mine with perpendicular blocks you can see laying across the underside, beneath the steering column. 

Here's a view on the pinion gear meshed with the rack, it's important to make sure the pinion has enough torque to turn the whole system. Locking gears, and jammed motors are a nightmare to builders.

Steering drives, while not an easy build for most people, really provide versatility to the bots you make. In the future, we'll explore some more steering systems, like the differential pivot wheel, and reversing motors. 
I'll leave you with a video displaying the turning radius and the piece movement involved with the execution of the drive:

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