Thursday, March 29, 2012

Constructing a Geartrain

example of lego gears
Gear trains are really REALLY helpful. If you're a serious Mindstormer, then I guarantee you have used gear trains and that you'll continue to use them extensively. I've mentioned them a lot in some of my other pieces, but I felt like the topic merited it's own post.

Gears are classified by the number of little ridges or "teeth" on them. Common Lego gears include the 8t, 16t, 24t, and the largest: the 40t.

Constructing a gear train is all about ratios. If you mesh an 8t gear with a 40t one, you'll get an 8 : 40  or 1 : 5 gear ratio. (This also happens to be the highest ratio attainable with only two Lego gears).

Compounding gears will help you increase power or speed though. This is best explained with the diagram below:
Combining gears along the same axle will help you gear up or down, increasing power or torque as you do so. Remember that the more torque you get, you're sacrificing that much speed, and vice-versa. It's important to establish the ideal ratio for whatever bot you're creating.

Once you've mastered this, you can work on implementing numerous gear trains in the same system, a topic I've covered here.

Monday, March 26, 2012

The RCX

The RCX is my preferred base computer for Lego Robots. Lego has a more recent mindstorm computer called the NXT, and though the NXT is probably more user friendly, I don't think it matches the versatility and compatibility of the 2.0 RCX. 

Of course choosing your computer is mostly preference, however rcx motors are smaller and it's generally easier to build a chassis around these models compared to the nxt layout. The NXT does hold an advantage in that it's easier to program, however I don't feel like that pro makes the nxt the better computer.

Wednesday, March 21, 2012

Shifting Gears: the Transmission

Shifting gears with Lego is a complicated task, albeit with numerous effective solutions. Today I designed the transmission above, and I'm going to talk about designing your own transmission in this post.

Deciding your gear ratios is the first step. What kind of power do you want? What vehicle will be using this transmission? Is speed a concern? This transmission used two unique gear ratios:

Gear train #1:            24t:8t:40t:24t (3:1:5:3)
     - This gear train provides torque and power sacrificing speed. The 24t is part of the transmission and when you shift up, the gear train is discontinued while the 24t in the second housing shifts into place, completing...

Gear train #2:            24t:40t:8t:24t (3:5:1:3)
    - Here you increase the speed, as you utilize the mammoth 5:1 ratio you're getting in the middle. This transmission is completed when you've shifted up, and using 24t's on the same axle helps complete the train.

The basic design of all transmissions are the same. Utilize two independent gear ratios which you can switch between at the push of a handle/knob. These manual  transmissions can have an unlimited amount of speeds depending on how creative you wanna get.

Also, the two independent trains must be connected to the same axle you're attempting to drive. Failure to do this will result in no forward motion by your vehicle.

Transmissions are fun to play with, and if you can successfully build one and implement it in your Mindstorm bot, few things can match the performance. Here's a video of the transmission in action, and I look forward to using it in future bots:

video

Differential Drives

By far the most common drive system for Lego robots, the differential drive is probably the easiest to make. Utilizing two parallel drive wheels on either side of the robot, they can be powered separately, or use a single motor as well.

The diagram to the right shows what a basic differential drive looks like. Bevel gears placed in the central gear housing allow the axles to turn independently, enabling the robot to turn in place, and maneuver pretty easily.

The following chart is adapted from "Building Robots with Lego Mindstorms" by the Ferrari Brothers and displays the different behaviors of  a robot in accordance to its wheels (powered by the differential drive).

Using different combinations of speed and direction, the robot has the ability to cover any amount of space, and turns at any angle. All this in addition to being very easy to implement. 

I assembled an example of a standard drive, showing how you can use the bevel gears inside the housing to attach the axles, and connecting it to an RCX is as easy as sliding two beams through it. 



As always, I encourage you to send me your designs, and contact me with any questions/comments/concerns. Happy building!

Tuesday, March 20, 2012

Building Robots with Lego Mindstorms

I'm working on a new post for later today or tomorrow, but I wanted to put this out there beforehand.

Buy this book. This is a must have for anyone with an inkling of interest in robots or Legos. It goes in-depth on topics I regularly discuss here, and the authors have some of the nicest designs for Mindstorms I've ever seen.

Monday, March 19, 2012

The Skid Steer Drive

The Skid Steer drive is truly a classic drive system. Usually incorporating treads or 6 wheels, good examples of skid-steer drives in real life include excavators, tanks, and other utility construction equipment.

A common variation of the differential drive (more on that later), the skid-steer has:

-better grip on rough floors/terrains
-more torque and power, where friction uses up some of the motors power
-easily maneuverable, however programming a skid steer to go straight is a little tricky.

The one I built above uses two motors powered by the same RCX. The chassis is divided into three parts (seen here). Two different mounts for each independent tread, and a central mount for the RCX and motors.

The wider base provides stability, which is important for slow moving treads, and a low center of gravity keeps accidents like tipping, and slipping from occurring.

An example of a clutch gear.
Another important component of a skid-steer (and pretty much all drives) is to incorporate elements to keep your motor from jamming. If a tread or a wheel gets caught, but the motor keeps trying to apply power, there's a dangerous chance of a lot of broken parts. My design incorporates a clutch gear which provides a certain domain of resistance before the clutch keeps the motor spinning with no damage (regardless of the status of the wheels).

Finally, shifting gears, and increasing the ratio provides massive increases in power, sacrificing speed in the process. Because my motor is directly linked to the 8t, which turns the 24t, my gear ratio ends up like:

                                                                               8t : 24t = 1:3

Which basically means that my wheels are turning at 3x the power the motor is outputting.

Skid-steer drives are fun to build, and even more satisfying to watch in action, and I definitely recommend experimenting with a few of your own designs to get started. If you have any alternate designs or suggestions shoot me an email: ashwin.johri@gmail.com

Introduction to the Blog

Welcome to Mindstorm Mechanics- Engineering Downsized.

My name is Ashwin, currently a student in southeastern Michigan. There's not much to me, but I created this site purely out of my enthusiasm for mechanical creations of all kinds.

I started this blog as an effort to create and demonstrate different topics in mechanical engineering, utilizing Lego Mindstorms as a great tool for these designs. I'm a fan of Mindstorms for numerous reasons:

-They're user friendly
-They're easily programmable
-And it's easy to create and destroy projects with little effort.

In following posts, I aim to describe numerous different mechanical drive systems, different building techniques, a wide array of vehicles made possible, and as the blog continues to grow, I'll explore some programming pieces as well. 

I'd love for any feedback, and to receive designs and advice from other users out there, and you can always reach me at my email: ashwin.johri@gmail.com

Thanks for reading,
Ashwin