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Zennbot one, The Robomower Part 5

The weather was cooperating today, and I had some time to spend with the Robomower project, so I was able to make some progress. The first major step was to connect the Sabertooth 2×25, the BR6000, and one of the wheelchair motors to the wheelchair battery pack and see if I could make something move. I bought some 12″ servo extensions and cut off the servo end. With the first one of these I connected the BR6000 to the 5v power supply conveniently located on the Sabertooth. I connected another one between the throttle channel (left joystick) and the #1 motor control. The Invacare motors came with some really cool connectors that I really like and want to keep, so I opened up the control box and unbolted the ring terminals that held them in the controller. They attached very nicely to the Sabertooth’s power terminals.

The Dimension Engineering Sabertooth 2x25 motor controller and the Spektrum BR6000 Bot Receiver.

I consulted the Dimension Engineering website to set the DIP switches for the Robomower’s needs. I had a roll of #10awg stranded wire left over from a previous project. As I was getting ready to use this to connect the chair batteries to the Sabertooth, I realized that I did not have any sort of master switch. As soon as the terminals were connected, the whole system would be energized. This would be okay for testing today, but is not acceptable as a long-term solution. I went ahead and ordered a big, bad robot switch from the Robot Marketplace. Should be here soon! When I got all this together, it took only a few tries to get the correct motor on the correct control channel, and in the right direction. In a couple of minutes, I was using the RC transmitter to make a motor spin! Success! I disconnected the battery and turned my attention to the mower:

There is a whole lot of plastic on and around this mower! The vast majority of the outer housing appears to be there for cosmetics and to keep dust and dirt from getting on the batteries. Based on my teardown experience, I’d say it was largely ineffective. I discovered what I now believe to be an important safety tip:

Retainer Ring

Axle retainer rings: Be careful taking these things off!

When you go to pry the little retaining rings off of the axles, make sure you’re looking the other way, as those things depart with some serious velocity! One of them caught me on the lip, and I’m just glad that I learned my lesson there rather than on an eye. After reading this informative blog post on the topic of solar-charged battery powered lawn mowers, I had a hunch, so I removed the little PCB brain from the mower and connected the battery leads directly to the motor and, anyone want to hazard a guess? That’s right, the mower fired up!
The mower and the Batteries

This configuration worked!

So not only did I score a working motor, but also a pair of working 17.5ah AGM batteries! Nice! So it turns out that the controller was the part that had gone bad. Easy enough, it’s getting recycled.
Bad Brain

This is the part that had failed in the mower, leaving me with a good motor and pair of batteries!

With the mower stripped down to its bare essentials, it was time to take some measurements. I wanted the frame to be as narrow as possible so as to allow the blade to mow close to an edge or an object. On the other hand, a wider track would provide for more lateral stability, and reduce the chance of roll-over. So here we have the eternal compromise. The front wheels, when mounted, were 18″ apart, so I decided to use this as the width of the frame. This was also convenient, as the lengths of 1″ steel angle that I bought were 36″ long, so I could just hack them in half and have my cross-members.

But I am getting ahead of myself. The next chapter will be about frame construction….

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