It has now all come together! One last trip to radio shack to get some connectors, heating up the soldering gun to splice together some 24 volt wires and some ground wires, applying some Velcro, a few more wood screws, and I’ve got a lawn mower!
After the successful test of the mower motor controller, as detailed in the previous post, all that was left was to put it all together. Since the mower batteries had been discarded due to general poor condition, leakage, and scary noises :-o, the wheelchair batteries were now going to take on the entire task of powering the bot, the mower motor, and the logic. This meant that I somehow had to get 24 volts from the battery array, get it through the BOS, and then to the mower. I also had to run a negative back to complete the circuit. I also needed a tap to run the 5volt regulated power supply that was to power the mower motor controller and associated relay. I had also intended to power the RC receiver with this supply, but that didn’t work for some reason (more on this later), so it went back to the 5volt tap off of the Sabertooth.
I started by soldering a second AWG #10 stranded wire onto the output lead from the BOS (Big ‘Ol Switch) to provide power for the mower motor. This lead went from the BOS to the MMC’s relay, and then on to the mower motor. I also soldered in a red #23 tap to power the MMC and the Darlington transistor that controls the relay, as well as the Arduino-like RBBB that provides the control logic.
I also cut the ground wire, and split it into two #10 leads and a #23 lead. The #23, of course, provided the ground for the MMC, and the two #10’s went to the Sabertooth to power the wheelchair motors and to the mower motor. To facilitate any future modifications, I used positive/negative (male/female) tab connectors whenever possible.
During initial testing, I had the RC receiver connected to the MMC board, but was getting the same sort of strange behavior that I had seen in an earlier stage of development: One motor or the other would start to “creep” when it wasn’t commanded to do anything, or my old favorite, cranking one motor into full reverse when a signal was lost. Sometimes, it would do that even when the signal wasn’t lost, so I had to dive in and turn the BOS while the thing was spinning at full speed. I don’t recommend that…
The solution was to power the receiver off of the 5V tap from the Sabertooth board, despite the manufacturer’s recommendation against doing so. I’ll look into this further and see what I can find out. Meantime, everything seems to be working fine.
After getting it all hooked up, I went ahead and made a few modifications to the electronics section. Previously, the same strap that held the battery pack into the bot also held the electronics section in place, with a little help from the two nylon lifting straps that are attached to the battery pack. This actually used up some real estate for which I had other plans. I built a couple of “feet” for the board out of the same primed 1×4 scrap that the board itself is made of, to lift the electronics off the battery case lid, and allow the retention strap to lay flat against the battery case. I then used some high-strength Velcro to hold the whole thing down. It actually works really well, mainly because everything it pretty light weight, and therefore has very little momentum.
So with everything looking good, I dropped on the original hood from the mower (the Vader Mask), and attacked my front lawn. Here are the results!
Okay, so the Robomower is really just about done. There are a few things that I could still do, and a few that I probably will. The wiring needs a few wire ties here and there, just to keep things neat. I REALLY like the idea of an amber rotating beacon on the top, and maybe a small pair of headlights. There are also some decorating ideas that this thing is just begging for.
I may also involve the Arduino a little bit more. The Sabertooth will take inputs from a micro controller just as easily as it will take direct RC (PPM) inputs. I am already talking to the Arduino by way of the RC receiver, and I have a few ideas of how a level of processing might improve the bot’s performance. I would be able to create custom speed curves, and as my friend Will suggested, I could add a gyroscope to help it track more of a straight line until a turning moment is introduced. More to think about.
I was expecting that the mower attachment itself would be a disappointment. With all the hacking and slashing I had to do to get it to fit, I just kind of figured I would be using it essentially as a placeholder until I found something better to hang from the bot frame. I am very happy to discover that I was wrong. The mower does a very nice job of cutting, and also mulching. There is no bag, as you can plainly see, and I was dubious about the ability of this thing to actually lay down a nice, fine mulch. Again, expectations were exceeded. I do want o get the blade cleaned up and sharpened, though, but I am currently seeing little need to do much else in that department.
So a tremendously fun project is more or less at its end. Some of those little additions and improvements will certainly be incorporated, and there will doubtless be maintenance issues come up now and again, but for the most part, this one’s about where I wanted it to be. Thanks for reading this blog, and drop me a line if you have any thoughts or ideas!