Buying Toys II: Second thoughts

I still like spending other people’s money.

And, I like the idea of getting as many toys as possible when spending that money.

For example, consider the Timbot project at the Oregon Health and Science University. We can strap a PDA to the top of an RC truck chassis, add a camera and/or range-finder, and we have a mobile robot that can wander all over campus.

In the lab, I imagined that the PPRK would be the way to go. However, I’ve been continuing to dig around regarding the platforms available for building robots on. The chassis is not the interesting part of a robot; it is the utility of it’s sensors and actuators, as well as the programmability of it’s “brain” that matters most.

So let’s look at the PPRK as a platform: it has three drive servos in a novel configuration (cool, but possibly power-hungry) and relatively low clearance (so I imagine it doesn’t do well outdoors). I want to be able to mount a variety of different sensors on it, and reconfigure those quickly and easily. I have some design work to do, but given the platform, I’m going to have to be careful.

I like the BrainStem. At $80, it looks like a great interface to the ‘bot; it has 4 servo outputs, 5 digital I/O ports, the I2C bus, and 5 analogue inputs. This is good. But the PPRK base doesn’t look so practical. For example, it looks like there isn’t much clearance between the acrylic (?) top plate and the electronics inside; this means mounting equipment will be a job that must be done carefully. Furthermore, it’s expensive; this is, in part, because of the novelty factor of the platform. Admittedly, a holonomic drive is cool, but how much is it worth?

Enter Budget Robotics (http://www.budgetrobotics.com/). This online store provides only the bits of robots they feel they can provide as high quality components, but cheaper than you might find elsewhere. They design and manufacture all their own stuff. Cool. In particular, let’s compare prices on two platforms that are similar: the PPRK, and the ScooterBot platform from Budget Robotics.

	ScooterBot	PPRK
Platform cost	$55	$315
Controller cost	$80	Included
TOTAL	$130	$315

If I buy a bare BrainStem as a controller, I can buy a base from Budget Robotics for $55 that has two servo motors, and is ready for me to attach my cameras, range-finders, and everything else. The price difference is $185; that is almost the cost of a new Zaurus 5500, which is the PDA I would like to slave the BrainStem to. I have enough to either A) pick up a second ScooterBot chassis (which gives me two indoor bots), or a treadded chassis that can manage the broken paving tiles that cover the Kent campus.

I guess the short version is that I can afford enough controllers and platforms to have two or three robots where we thought we might only purchase one. That’s a real coup, I think, and means that more people in different research groups can experiment with mobile WiFi robots that have a variety of sensor and vision capabilities. When I finalise the purchase order for our robots, I’ll include it here.