Having purchased some of the Micro Metal GearMotors I decided to make a small mobile robot to try them out. As the motors are so neat I decided that I would try to make a mobile robot that was also 'neat' and try and make it look as nice as possible. Most of my builds are cobbled together and look rather haphazard so I thought I might try and make a nicer looking one with everything perfect, or as perfect as I can manage.
Below is the chassis that I have designed and 3D printed. I have created a small box that the motors just push fit into as I wanted to make the 3D print as easy as possible and also avoid any gluing. I tried making a tube to insert the motors into but the support material was difficult to remove from inside a longer tube, plus there were difficulties getting the motors in as there wasn't enough room to insert them. I also designed and 3D printed my own wheels as I had already purchased some rubber O-rings. This was only my second attempt at making some wheels (my first was for Tiny24hourMobot and they were not that good) and I think they have turned out pretty good. They are just push fit onto the D shaped axle of the motor. They are a tight interference fit and with the longer axle hub they seem to work well leading to minimal play.
Having 3D printed the chassis and wheels I wanted to try out the motors as soon as possible so I have just connected them directly to a battery pack. The size of the chassis was mostly determined by the DC motors which give the width, and the size of the wheels which give the length. Originally I wanted to make it as small as possible but I currently only have one size of O rings for the wheels and the motors cannot be put much closer together. The minimum size turned out to be almost the same size as the 4 x AA battery packs that I use so I thought I would just enlarge the chassis a little until it was a good fit for the battery pack. As can be seen from the video below this has worked out well. I have just used a white protoboard to connect all the wires together, remembering to reverse the connections for the motors on opposites sides as they are mirror images. It seems to work well. This video shows a first run onto grass. Well, it is four wheel drive so I thought it might be OK. It managed to start with but then the grass was just a bit to long, but it shows potential. With slightly different wheels (bigger?) and tyres (with some more tread pattern) it can probably manage short grass.
For a second run I tried it on some block paving, see the video below. It copes well with the paving and some soil. It doesn't quite travel in a perfectly straight line but that would be difficult to achieve as everything would have to be perfect, but it is fairly close to a straight line.
The DC motors do slip out of their boxes, as I suspected they would, so now I will 3D print a flat bottom plate that can be screwed to the existing chassis and hold the motors in place. I will then have to think about the wiring and controller, and how to make it look nice, rather than the current mess.