Servo - September 2015

planned. Of course, I still needed to add the lift and gripper mechanisms and the spider body. I made a quick calculation of the combined weight of the yet-to-be-added components and loaded down the chassis with the equivalent in lead. It was now time to test it again to confirm that all was still on track. I pushed the throttle forward expecting it to speed down the sidewalk once again, but was sorely disappointed!

It moved, but even a toddler could outrun it now!

It was time to return to the drawing board and attempt to resolve the speed issue. I was so pleased with the speed and agility of the bare platform that I didn’t want to sacrifice it. Something had to give.

We Need More Power, Captain!

I concluded that I had a couple of options open to me. Either add larger and more powerful motors or significantly lighten the load. My unrealistic expectations regarding the ability of my chosen RC platform to carry all the extra weight proved I still had plenty to learn when working with this new base. I now have even more respect for the BattleBot designers that can include all that steel and weaponry and manage to have a quick robot!

I still believed that the Scout robot was up to the task, but I would need to greatly reduce my design in order to control the amount of weight I expected it to carry. It was time to scale back and cut out all the spider’s fat!

The original plan was to use one of the many spiders I had on hand in order to save some money and speed up the build process. The spider I chose was very large and menacing looking, which provided the effect I was after.

However, it included some steel reinforcements which added considerable weight. It also had a soft foam body which would make it difficult to install around the mechanics without interfering with their operation.

I then conducted an extensive and fruitless Internet search to try and find a suitable replacement. When I came up empty, I decided to try and recruit my wife to help me construct a custom model. This turned out to be the perfect solution to my problem!

Before we started the construction of the spider, I took another look at my plan to use a linear servo to lift the front of the arachnid. If I was going to go with a lighter one, was there another option? I’ve had great success using the servo powered gearboxes from the Actobotics line at ServoCity for my articulated bodies. I figured it would have the necessary torque to raise the body, now that I’d replaced my original spider with a much lighter one. I mounted it up, attached some weight to the lifting arm, and gave it a test. It handled the load like a champ, with the added bonus of requiring much less juice — allowing my batteries to last significantly longer.

It was now time to build a framework to attach the channel to which the gearbox and gripper would be affixed. I started with two pieces of 12 inch channel and cut them down until I was happy with the proportions. These were simply connected with a hinge, giving it a very wide range of motion. Connecting the servo horn on the gearbox to the upper channel was easy once I had the mounting point selected by using 6/32 threaded rod and ball linkages. I then built a protective structure around the servo to allow the body to be attached without interfering with the mechanism.

The gripper kit was a snap to assemble (again, thanks to the easy-to-follow video instructions). After only a few minutes, it was ready to pinch away (Figures 3 and 4).