My little robotic pals

Years ago I decided to build an indoor robot with multiple kinects for navigation and a robotic arm for manipulation. It was an interesting time working out how to do this and what is needed to get a mobile base to map and navigate a static and dynamic indoor space. Any young players reading this might think that ROS can just magically make this all happen. There are some interesting issues to discover building your own base and some, um, "issues" shall we say that you will need to address that are not in the books or docs. I won't spoil it here for the new players other than to say be prepared to be persistent. 

There are two active wheels at the front and a single drag wheel at the back about 12 inches behind the front wheels. I wrote the code to control the arm myself as custom ROS nodes. A great trick here is you can inject sinusoidal movement by injecting a shim ROS node to take one target and smoothly move towards it.

Now I have a new friend for outdoor activity, the "hound bot". The little furry friend is still sans hair but has gps, imu, rc control override, and a ps4 eye camera mounted for depth perception and mapping. Taking a leaf out of one of the big car makers book and only using cameras for navigation. But for me it is about cost since a good lidar is still much to expensive for the hound.

The hound is a sort of monocoque where the copper looking square part at the front is part of a 1/4 inch aircraft grade alloy solid welded chassis that extends the lenght of the robot. The hound can do about 20km/h and is around 20kg in heft. The electronics bay in the middle is protected by a reinforced carbon fibre layup that I did. Mixing material for fun and slight weight loss.

One great part about doing this "because I want to" is that I am unbounded. Academic institutions might say that building robust alloy shells is not a worthwhile task and only the abstract algorithms matter. I get to pick and choose what matters based purely on what is interesting, what is hard to do (yay!), and what will help me get the robot to perform a task that I want.

The hound will get gripper(s) so it can autonomously "fetch" things for me such as the mail or go find and pick up objects on the lawn.

The Gantry is attached!

Now the fourth axis finally looks at home on the CNC plate.  The new gantry sides are almost 100mm taller than the old ones and share a similar shape. While the gantry was off the machine was a good time to attach the new Z-Axis which gains a similar amount of Z travel. Final adjustment of where the spindle sits in its holder are still needed but it makes sense for the cutting edge to be fairly high up when the Z-Axis is fully retracted as shown.

After a day of great success early on a day of great problem solving arrived before the attachment was possible. The day of great success involved testing the two new sides to see if or how well they attached to the mount points at the base of the machine. These holes in the gantry were hand marked, drilled, and tapped so there was some good chance that they were off target enough to not work well. But those all went fine.

The second success was mounting the Z-Axis to the existing points on the gantry. I had in the back of my mind the thought that one side (the three holes on the bottom of the mount) to line up and attach fine but the top holes to be out of alignment. Both of these plates, seen in horizontal in the image above, were made by CNC so the holes should be where I intended. Though these plates were both mounted to the Z-Axis and the bottom plate goes right through to the lower steel bracket so the alignment might not have been 100%. I registered both plates to the smooth side of the spindle backing plate so the alignment in that axis should have been ok. To great surprise and joy the top holes also aligned perfectly and the second phase fell into place.

It was only when putting the new sides onto the gantry that interesting things started to happen. I will have a new blog post on that part soon and likely a video of the problems and solutions for that part. One thing I will say now is that it helps to have washers, bolts, and spare skate bearings on hand for this process depending on how you have designed your far side gantry upright.