I like gadgets - not normal gadgets like iPods and Zunes and smartphones (although I have my pile there). I like things like robots and robot arms and synthesizers and DIY synth kits and synth kits based on classic Commodore chips, and Netduino and FEZ .NET Micro Framework boards and more. Well, you get the picture.

I've always thought robotic arms were very cool to play with, and make awesome geek desk accessories. Unfortunately, most servo-based arm kits run in the > $400 category once you pick actual arm lengths, add the gripper, base, and optional rotating wrists. While those kits have a lot of potential, and are typically powerful, you can get a lot of enjoyment from an inexpensive gear-motor based arm.

I've purchased two robotic arms lately, the newer OWI-524 and the larger but older and still available OWI-007. I'll have them with me at MADExpo at the end of the month.

NOTE: When I wrote this, for some reason I thought it was listed as a 524. However, I see that it is more commonly listed as a 535. I have no idea why the discrepancy, but this post certainly applies to the 535 as well.

Here's the OWI company's photo of the OWI-524. It is a bright bumblebee-colored arm with a matching remote control. The yello shapes at the joints house the motors and gears.

Since OWI itself no longer sells or lists the OWI-007 Trainer and presumably no longer manufactures it (lots of places still have it in stock, though), here's a found photo of the OWI-007, from one of my other favorite robotic bits sites, pololu.com

Physically, the OWI-524 Edge is a smaller unit, but much more colorful and modern looking, made of black and yellow opaque plastic (feels like ABS). The OWI-007 Arm Trainer is more basic in appearance, but larger. It is made of smoke-colored plastic that I assume to be polycarbonate, with a few parts made of a self-lubricating white plastic (not sure if it is HDPE or nylon or something similar, but it's not the poly carb). The Edge has a single LED light that can illuminate what it is going to pick up. The Trainer has a single light bulb for each motor, to show which one is in operation at that time, but no lamp to illuminate the target.

The two are shown side x side on my messy desk. You can also see both remote controls, although the Edge is using USB (and is gripping a USB drive for some sense of scale), not the remote here.

Operation

Both arms make use of five motors, but in slightly different ways. The 524 has a bendable wrist, where as the 007 has a rotating wrist. One is not necessarily better than the other, although I like the look of the rotating wrist. That said, in practice, the bending wrist makes it easier to grab stuff.

The OWI-524, while smaller, has more range of motion.

Manual Operation

Both kits have wired remote control boxes. In fact, these control boxes are the most similar thing across the kits, with both using the same type of circuit board construction and almost identical molds for the case. The remotes are simple, with a number of kit-build momentary switches based on power circuits completed with leaf springs of metal being pushed down by levers on the control surface.

In case it matters, the 524 Edge has a power switch, the 007 Trainer does not.

The single biggest difference ion how the two operate, in terms of nuts and bolts, is the trainer uses clutch plates and gears to handle over-extension situations, whereas the Edge simply lets the gears pop and slip. Of course, this means the Edge gives you feedback when you go too far (but the sound of grinding plastic gears sets my teeth on edge) whereas the Trainer simply fails to move any further, as it lets the clutch slip. The gears on the Edge can likely take it, but I hate that snapping sound and the slight jerking of the arm when you move too far (which my son does all the time with it)

The 524 Edge is faster and has a more pleasing motor sound than the 007 Trainer.

Manual operation is fun, especially for kids. Most of the readers of my blog, however, are going to want to hook these up to PCs or microcontrollers at some point.

USB Operation

Both the Robotic Arm Edge and the Trainer offer USB interface options. The OWI-524 Edge version is a small card that replaces the onboard (simple) power routing circuit. The OWI-007 Trainer USB card looks to be more involved, and is external to the unit itself. It also lists for quite a bit more. (See info in purchasing for more options)

I'm not sure if the trainer USB interface comes with any control software or any API. I've seen a low-res movie of someone using a parallel port interface. However, since the 007 dates from circa 2005 (at least according to the date code on the box I have), it predates most YouTube content by a long shot.

Keep in mind that we're working with regular DC motors here, not servos. The high-end arms have servos which can report position and hold exact positions based on degrees. These are geared down DC motors, with a fair amount of slop in the gears and after run while the gears spin down.

I haven't hooked the 007 up to USB yet (I just built it tonight), but the USB application for the edge is a nice replacement for the remote control. Unfortunately, it has kid-friendly sound effects that quickly get annoying, and have no option to turn off. The program does have some other nice (and kid-friendly) features, however.

Robot Arm Edge USB Remote Control App

The remote control app for the edge has two modes: Basic and Program. Basic is a simple USB replacement for the remote control, allowing you to use your mouse to move the arm.

As you can see, the app is a small (800x600) nicely-designed interface to the arm. Hovering over the icons at the bottom highlights the appropriate part of the arm in the photo.

Note, that I did have some issues with the Edge being detected by Windows 7 x64. Download the new driver from the OWI support site, do not install the driver from the CD. If you install the driver on the CD, uninstall it and manually delete the driver from the Windows Device Manager. Even after that, I ran into some issues with detection on 64 bit Windows, and if I disconnect it, there's almost a waiting period of several minutes before I can use it again. I think OWI's driver is less than flawless here.

The program mode is very cool, especially to teach programming to children. The basic workflow is to use the mouse to hover over a joint, then select the direction until you've moved it to the desired spot. Once you have the movement for that joint for that step, you either add, insert, or overwrite the current step by selecting the button at the bottom. If you add, the step is added to the list.

Once the steps are complete, you can hit rewind to get back to the starting position. Remember, as these aren't servos, the positions are all relative, not absolute. For that reason, the rewind is pretty critical. Frankly, it's also cool to watch :)

I didn't show it here, but you can also stack movements in a single step. In that case, you simply create several movements (one per motor) and add them all at once. They appear side by side in the list and happen simultaneously, which is pretty impressive to watch.

From what I've read, it appears there's a limit of 99 replays for a single script in this program. I assume that is to prevent it from being used in industrial (HAHAHA) or permanent exhibit situations.

Programming the Edge from your PC

While the OWI-007 had a parallel port protocol that was understood and used by others (but not published), the USB protocol used by the Edge (and presumably the same used by the OWI-007 later USB interface board) is not something published by OWI. However, fear not! People have reverse engineered it. I haven't gone through the programming effort just yet, but likely will soon. I mean, I have to, you know? :)

In case you want to try, here's a promising library for USB communication.

Please note that the software that controls the OWI-007 Robot Arm Trainer via USB requires the .NET framework, so there's potential there for sure (you download the software from OWI directly).

Programming Either from your Micro Controller

In both cases, the base interface everything uses to connect to the arm is simply sending a voltage across a pin to directly control the motor. Any number of motor control boards for your micro controllers could handle this. As both robots run off of four D-size batteries, that puts the voltage requirement at 6v. That's more than I'd want to directly drive out of my microcontroller (plus I'd want feedback protection) so a simple motor controller or even a set of home-made H-bridge circuits would do it.

Other Programming Models

Some sites, such as Kits USA offer speech control units for the OWI-007 trainer. I personally think you'd be better off using Windows 7 speech recognition from .NET and running the trainer from your PC.

Ok, enough on use. Before you use either one, you need to actually build the arm. The build processes between the two are very different.

Construction

The OWI-524 Edge comes sprued and bagged, much like a large model kit (no glue required), with the addition of loose parts in bags (gears, pins, motors, screws, etc.). Some parts, specifically the gripper, are reused on other OWI kits, so they can good return for the injection molding. To assemble the model, you'll follow clear instructions that include everything you'll need to know for even your kids (assuming they're of model-building age) to build. It's all screws and alignment pins, no glue.

The Trainer comes with all the parts separated, carded on a single sheet of labeled cardboard (which I neglected to photograph before assembling the arm tonight). Like the Edge, no glue is required for assembly. The polycarbonate parts feel tougher/stronger than the parts used in the Edge, but it's not like you'll be swordfighting or lifting weights with either one. However, despite the parts already being desprued, I found this one more fiddly to assemble, with instructions that, while excellent, weren't quite as clear as the Edge instructions. I mention that only because it may be slightly harder for children/teens (recommended age is 14) to assemble. That said, there are far fewer things to assemble on the 007 trainer (gear heads on the motors are pre-assembled, for example), so if you want to go from zero to ruling the universe in a minimal amount of time, you'll get there faster with the trainer.

Each took a few hours in front of the TV (probably an hour or so more for the edge), sometimes watching my kids, sometimes after bedtime. Neither is very difficult to assemble, as long as you have a few basic tools (side-cutting snips for despruing with the edge, small needle-nose pliers and a small philips screwdriver in both cases)

I did appreciate that the 007 Trainer used the same size self-tapping screws in all locations, where the 524 Edge used several different sizes and shapes, some easily mistaken for others if you aren't careful.

Purchasing

The most inexpensive place I've found to get these two arms is Kits USA. They have, as of the time of this writing, the OWI-524 Robotic Arm Edge for $30 and the OWI-007 Robotic Programmable Arm Kit for $60. They also sell the USB and speech interfaces separately, or with the arms themselves. Note that I actually purchased my OWI-524 USB interface from OWI directly. They have a smaller unit that requires you to replace the onboard circuit board. The one Kits USA sells appears to be an external board, and which may actually be more flexible. I haven't tried it to check.

OWI has a few other cool and inexpensive "robot" kits as well (I have the beetle and the tracked crawler). Just stay away from their little 6 in 1 solar kit, it's complete crap.

Conclusion and Recommendation

If you're buying for yourself, you may like the older 007 a bit more, as it feels more like a real robot arm. If you're buying for your kids, especially ones you want to teach programming to, get the Edge and the USB control application. The arm is more colorful and less intimidating to look at, and the control app is great.

Of course, for a very basic DC motor robotic arm, you can't go wrong with either of these. I have both, and won't part with either of them :)

You can find a number of videos on YouTube, mostly of the newer OWI-524, by searching for owi robotic arm.