The primary advantage of autonomy is obvious: the removal of a human from the machine. But that’s not where the benefits stop. Think about what a military drone looks like compared to a fighter jet. If you can get rid of the pilot, you can get rid of the seats, the yoke, the visual instruments in the cockpit. You don’t have to pressurize the cabin anymore. Shoot, now you can change the whole configuration of the aircraft to gain efficiencies you never even imagined when you had to design around a human in the cockpit. Notice how the propeller is on the back side of the drone, whereas it’s on the front of the manned aircraft?

I’ve been watching several folks develop autonomous lawn mowing solutions over the past few years. Back in 2014, Alligator over at the Rusty Nails Workshop attempted to make an autonomous lawn mower using an electric push mower deck with a Piksi RTK GNSS module, the cutting edge in positioning technology in 2014.

More recently I’ve watched the venerable Kenny Trussell and Robby over at Deep South Robotics fully automate a ZTR mower for their acreages. I’ve also been paying attention to the folks out at MowBotix who are attempting to commercialize their solution, which appears to be similar to what Kenny and Robby have come up with.

Each one of these solutions begins with an off the shelf mower. That seems to be a logical place to start: cutting grass is kind of a solved problem. And if you use a riding mower, you get the drive wheels for free, eliminating the need to come up with a way to propel your mower like Alligator and I had to.

Along the way I have questioned whether making a clean sheet design was the right way to approach this problem. There’s no doubt it will be more expensive in the short run. I’ve spent close to 300 hours designing the robot lawn mower over the past year and a half, and once everything is finished I will probably have close to $4,000 tied up in it.

But there is one thing that you can’t beat with a clean sheet design: The opportunity to toss out all the baggage that existing mowers come with and explore what an autonomous lawn mower could look like if you take the person out of the equation.

The Baggage

If you look at a typical ZTR riding mower, you see many familiar features: a nice plush seat to sit in, foam covered control handles, a deck to place your feet on with a nice grippy surface.

Look closer and you’ll find some very deliberately designed safety features, such as a dead man switch under the seat and some guards placed in areas you might get your foot too close to the mower blade.

If you look even closer you’ll discover that because of all the features described above, you kind of have to put the engine far away from the deck spindles. And that forces you to have an intricate pulley system to transmit power to the mower blades.

And your wheel base has to be pretty large in order to create room for a person to drive the thing. Your tires and engine have to be oversized in order to support the weight of an operator that could possibly weigh 200lb+.

Long story short, mowers manufactured today are designed with a significant constraint in mind: the operator. If you remove the operator, you can eliminate those constraints, and you end up with a machine that is much more efficient in almost every respect. The table below is just the weight and size differences between the prototype robotic lawn mower and the mower pictured above.

The prototype robotic lawn mower is half the weight and less than half the foot print of the ZTR mower, while featuring a deck that is the same width. With the right deck motors and batteries, the 14.5hp power rating could be matched, too. However, I suspect part of the reason you need so much power on a riding mower is because it’s larger, and you have to have a person sitting on it the whole time.

The biggest advantage to automating lawn mowers is obvious: you don’t need a person controlling the mower anymore. But if we’re going to remove the person from the equation, let’s take that leap all the way to it’s conclusion. There are huge design efficiencies you can gain by eliminating the operator. Let’s redo the whole system to take advantage of all of them.

When you google “robot lawn mower” you will find a bunch of Roomba looking robots like the one above. The missing ingredient between these robots and the one I’m attempting to make is one thing: positioning.

When you need your lawn mowed, you want it to be mowed 100%. You don’t want half the lawn cut and the other half not cut. You don’t want gaps of uncut grass between your stripes. You don’t want random paths cut through your lawn. You want nice, parallel, alternating stripes.

To accomplish that, you need to know the location of the mower throughout the process so you can keep track of areas that have been cut, and so you can cut the grass in a specific manner. Back and forth stripes, for example, or perhaps a nice circular spiral moving outward from a tree.

I’ve come to the conclusion that to really automate the mowing process, you need at least +/-1in of positioning accuracy. Historically, such a system required a $40,000 survey grade GPS system from Trimble or Leica and the equivalent of a master’s degree in computer engineering to integrate it into your robot.

So the Roomba mower guys, given these constraints, came up with the following solution:

Who cares where the mower is? Just fence it in and have it mow all the time. You’ll eventually cut all the grass. We gotta make a product that we can realistically sell to people at a profit, you know.

-Some engineering manager out at Roomba Mowers Inc, I’m guessing

Every robot mower has to compete with the neighbor kid that will mow your lawn for $20. He’ll even try to make the stripes in the front lawn mostly straight and parallel. That’s the price point and level of quality that you have to beat with any robotic mowing system.

The Roomba mower guys sacrificed quality and scalability to get there with their system. Those are probably decent tradeoffs if we’re honest. While these Roomba mowers are for the most part a novelty, for some folks they work okay. But in the scenarios where they do perform well, they’re probably not value added at their $2,000+ price point.

So for years, guys like me that dreamed of real robot lawn mowers were left with just that: dreams. I don’t have $40,000 laying around, and I’m a mechanical engineer, not a hardware guy or a computer engineer. And even if I had both of those things, such a system can never turn a profit in the market place.

Enter u-Blox with the ZED-F9P module….