Building with Repurposing in Mind

March 2011
by Bryan Bergeron, Editor

In these cost-conscious times, the economics of robotic experimentation may be at odds with your budget. A DIY robot with microprocessor, a few sensors, and two or more servos can easily run $100 or more in parts. And once you’ve built and tested your robot, you’ll inevitably want to upgrade or significantly improve the design. That’s when it starts to get expensive.

You can minimize your total cash outlay by building your robots with repurposing in mind. That is, assume your robotic creations are temporary, and that one day soon you’ll be using all or some of the parts in some other robotics project. Tearing down one of your robots needn’t be an arduous, lengthy task if you go about your prototyping with repurposing in mind.

One obvious approach is to use a solderless breadboard for your work. The larger boards with aluminum backing and multiple binding posts for power can be great for basic circuit prototyping, before you deploy the circuit on a mobile platform. However, except for small boards, breadboards are often too cumbersome and heavy for deploying on a robotic platform. The solderless breadboards that are integrated with the robots from Parallax (http://www.parallax.com) and the mini 1.8”x1.4”self-adhesive breadboards from SparkFun (http://www.sparkfun.com) are useful, but limited in component capacity. When you need to work with more than a dozen components or with unwieldy components that don’t insert neatly into a solderless breadboard, you’ll have to turn to other options.

You can avoid soldering ICs directly into a circuit and use IC sockets instead. I don’t use the gold-plated variety, but whatever is on sale from suppliers like All Electronics (http://www.allelectronics.com). At 15–20 cents, sockets are a no-brainer when it comes to repurposing ICs. You’ll spend that much on solder-wick if you try to unsolder an IC from a board, and you may damage the IC in the process.

One step up from IC sockets is to use breakout boards, or miniature circuit board modules with connections to all or most of the pins on an IC or other device. I like to use breakout boards from SparkFun, but instead of soldering wire to the boards directly, I add headers so that I can use cables with connectors. That way, I can move the modules from project to project in minutes. This module approach is especially useful for power supplies.

Many of the sensor breakout boards from Parallax come with headers designed for easy insertion into breakout boards. These work fine as long as you can fit your creation in a breadboard. However, the vertical pins can be difficult to work with cables and connectors, unless you can mount the board upside down.

Another way to avoid soldering directly to components is to use wire-wrapping to connect components, sockets, and pins. You’ll need to invest in a wire-wrap tool ($6 at RadioShack) and 30-gauge wire-wrapping wire ($9 for a 100’ spool; SparkFun). The great thing about wire-wrapping is that once you get the hang of it, it’s much faster than soldering. And you can quickly and harmlessly unwrap wire from a pin or component. There’s no soldering iron, fumes, or potential solder splashes to deal with – all pluses for experimenters of any age.

The downside of wire-wrapping is that the tool and special wire can be expensive – be careful where you shop. The same tool available from RadioShack for $6 sells for $16 to $56 on some websites. Another issue is that 30-gauge wire has limited current carrying capacity. You’ll want to consider heavier gauge wire and solder or crimp-on lugs, and other substantial connectors for battery and motor connections.

When possible, use terminal blocks instead of soldering wire to expensive circuit boards. For example, the screw shield for the Arduino — available from The RobotShop (http://www.robotshop.com) and others — is a handy prototyping tool if you work with the Arduino. In fact, shields in general are a great way to repurpose your microprocessor boards. Simply unplug the shield and move your processors to your next project.

My last suggestion is to document what you build. Sketch a schematic of your device before you retire it. With schematic in hand, you won’t have to examine your collection of robots to find the one with the 3V power supply, or the one in which you used the 16 MHz version of a processor.

At some point in your prototyping, you may develop a ‘keeper’ – something you’ll never disassemble for parts. When you reach that stage, a custom printed circuit board and soldered components will usually provide the best reliability and smallest footprint. Good luck with your projects. SV

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