Robots as Spaceships: Terrestial Motive Systems

There are many jokes about physicists and frictionless vacuums. Space is the rare environment that is a frictionless vacuum, and that makes calculating spaceship movement strangely simple, if foreign to those accustomed to terrestrial movement. When on the ground, a host of forces acting on a vehicle create a complex environment to move through.

A complex environment many of us have an intuitive grasp of, and we notice when things are a bit off. We plan to use Spaceship's Motive systems in a lot of our robots, and its worth tweaking a few of the numbers.

In this article, we'll be looking at tracks, wheels, and legs, the simplest and most common motive systems for robots in fiction (along with hovering, which suspends disbelief about its performance along with everything else). Legs come from spaceships 4, while wheels and tracks come from Pyramid  3/34.
We will be looking at both speeds and costs.

Down Shifting

The top speeds given in pyramid 3/34 appear fairly high. For instance, The top speed for a bot with only one one power system and a single tracked drive-train is 20 miles per hour. This is a pretty high minimum speed. Wheeled drive trains start with a top speed of 46 mph (for something designed to drive off-road) and go up from there. This pattern continues across many motive systems.  So we will want to "Down Shift" many of the speeds to match what we expect out of vehicles.

Wheels:

Down Shifting

Right now the minimal top speed for a robot with a wheeled drive train is 23 yards/second, or 46 miles/hour. That system takes up 1/10th of the robot's mass, is designed to drive off-road, and isn't even streamlined. This feels a bit high.

We downshift the wheeled drivetrain by raising the number of power points required for each acceleration and speed combination by one. A streamlined vehicle with two wheeled drive trains and three allocated power points now has a top speed of 104 miles per hours instead of 120.

When a downshifted wheeled drivetrain is only getting a single power point, it has a move of 1/15if streamlined and 1/10 if not.

Normalized Cost

Currently Wheels are by far the cheapest motive system we have access to, and only to screws and ballast tanks come close. Everything else is an order of magnitude more expensive. Wheeled drive trains shouldn't be particularly expensive to put on your robot, but as it stands, they are ridiculously cheap.

Normalized Wheel Costs makes wheeled drivetrains cost 5 times as much  as in Pyramid 3/34. This brings them more in line with other motive systems, comparable to tank tracks. Because control rooms already cost 20 times as much as wheels, this won't raise the cost of even minimal vehicles by very much. As a side benefit, it will make a lot of chassis's have much rounder totals.

 Normalized Cost Wheels have a base cost of 5, if you're using my house rule for scaling spaceships easily.

Tracks:

Down Shifting

Tracks are perhaps the classic way to outfit a robot. The top speeds here are comparatively tamer, but still feel a bit high, especially at high power. While the top speeds for wheeled drive-trains on unstreamlined vehicles are notably slowed by wind resistance at about 80 miles per hour (move 40),  Tracks continue a smooth progression up until 100 miles per hour (Move 50), and ultimately have a higher top speed if the vehicle is unstreamlined.

For top speeds of  downshifted tracked drivetrains, use the top speeds of the unstreamlined wheeled vehicles for two power points less (unmodified). So a tracked drivetrain with four power points has a top speed equal to a wheeled drivetrain with no streamlining and two power points, or 35.

Legs

Down Shifting

Using the movement rules from spaceships, even the slowest legged robots have a move of 5, using only two systems, or about 10% of their weight. Humans acomplish about as much with 30% of their weight in their legs, which is the equivalent of five or six systems. Slow moving legged robots are a staple of science fiction, and we need a way to build them in our system. We have not only reasons of realism to slow down legs, but also genre motivations.

Downshifted legged robots have speeds as though they had one less leg system. It takes two downshifted leg systems to have a move of 5, rather than one, and four downshifted leg systems to have an top speed of 15, rather than three. Robots with a single downshifted leg system have a move of 3.

Double Downshifting

Settings that wish to have legged robots but emphasize just how technically difficult this type of movement is may double downshift their robot legs, lower the speeds of legged robots again. Double downshifted legs have moves through the speeds in spaceships 4, but as though they had two fewer leg systems.  Two double down shifted leg systems a move of 3, and a single double downshifted leg system has a move of 1. Alternatively single double downshifted legs do not grant any move at all.

Cheap Legs

As written, legs are very expensive. This is not an unrealistic pricing, but in some settings legs are favored for aesthetic reasons. In these settings, the price (And thus base cost) of legs should be reduced to 1/5th ("Cheap Legs") or to 1/20th ("Cinematic Cheap Legs")  of the values given in spaceships 4.

Cinematic Cheap legs cost as much as tracks, or as Normalized Cost Wheels.

Moving On

I hope these numbers help you to build robots, spaceships, and other vehicles. Movement is one of the most important parts of a vehicle, and these things will now move better!

Happy Vehicle Construction!