Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you'd like to add some robotics stocks to your portfolio but don't have the time or expertise to hand-pick a few, the Robo-Stox Global Robotics & Automation ETF (NASDAQ:ROBO) could save you a lot of trouble. Instead of trying to figure out which robotics stocks will perform best, you can use this ETF to invest in lots of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual-fund cousins. However, this ETF, focused on robotics stocks, sports a rather steep expense ratio -- an annual fee -- of 0.95%. The fund is fairly small, too, so if you're thinking of buying, beware of possibly large spreads between its bid and ask prices. Consider using a limit order if you want to buy in.

This ETF is too new to have a track record sufficient for assessment. Investors with conviction need to wait for their holdings to deliver.

Why robotics stocks?
Robotics companies and their related robotics stocks have been in the news a lot lately, with pundits and researchers seeing them wiping out many jobs in the future or coexisting profitably with us.

More than a handful of robotics stocks had strong performances over the past year. 3D Systems (NYSE:DDD) surged 149%, largely on steep expectations. The 3-D printing specialist is seen by some as overhyped and overvalued, but others like its focus on both industry and consumers and its recent acquisition spree. For example, it recently snapped up a strategic chunk of Xerox, a company with more than a bit of printing expertise. 3D Systems posted big growth numbers in its third quarter, but it also tempered near-term expectations. 3D Systems is significantly shorted, with some worried about Hewlett-Packard's entry into the market and others concerned about some insider selling, though that's not necessarily a bad omen.

ExOne (NASDAQ:XONE), another 3-D printing specialist, has more than doubled over the past year. With its forward P/E of 140 and no current P/E due to negative earnings, ExOne doesn't appear to be a bargain. Its third quarter did feature an operating profit, though, and sales, though small, are growing briskly. CEO S. Kent Rockwell noted, "We continue to aggressively execute on our stated strategic plan -- increasing machine sales, expanding our production capacity and PSC network, and building our material and binders portfolio." Within the 3-D printing business, ExOne has an industrial focus. Bears worry about patent expirations and note that it's still very small -- it sold just 13 printers in 2012 and 17 in 2013, as of last quarter. The company is newly public, too.

iRobot (NASDAQ:IRBT), up 84% over the past year, is known for its Roomba consumer vacuums, but it's also involved in the health care and military sectors, among others. Raymond James analyst Brian Gesuale recently gave iRobot a "Strong Buy" rating, in part due to expansion in other countries including China, as well as new product lines like the Braava robotic mop. The stock soared recently on news that Google bought another robotics specialist. Many are bullish on iRobot's future, though it's still young and surrounded by more uncertainty than many other companies.

Other robotics stocks didn't do quite as well over the last year but could see their fortunes change in years to come. Robotic-surgical-equipment leader Intuitive Surgical (NASDAQ:ISRG) sank 23%, hurt by bearish comments by a research company, questions about the efficacy of its systems, a warning letter from the FDA, and even product recalls, among other things. Still, Intuitive Surgical has been posting some solid performance numbers, with revenue and earnings growing by double digits in recent years. Investors need to decide whether the company's issues are long-term or temporary. Uncertainty can represent opportunity -- sometimes.

The big picture
If you're interested in adding some robotics stocks to your portfolio, consider doing so via an ETF. A well-chosen ETF can grant you instant diversification across any industry or group of companies and make investing in them -- and profiting from them -- that much easier.

Longtime Fool contributor Selena Maranjian, whom you can follow on Twitter, owns shares of Google, Intuitive Surgical, and iRobot. The Motley Fool recommends 3D Systems, ExOne, Google, Intuitive Surgical, and iRobot. The Motley Fool owns shares of 3D Systems, ExOne, Google, and Intuitive Surgical and has the following options: short January 2014 $20 puts on 3D Systems. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.