Servo - August 2011

Our resident expert on all things robotic is merely an email away.

roboto@servomagazine.com

Tap into the sum of allhumanknowledge and get your questions answered here! From software algorithms to material selection, Mr. Roboto strives to meet you where you are — and what more would you expect from a complex service droid?

by

Dennis Clark

I didn’t have a lot of questions this month, but what I did get sure caused a bunch of research. I wish that I had time to program up some examples, because they would be very cool. So much to do, so little time! I hope that everyone is busy building and programming bots and that is why it has been so quiet.

Robotics is composed of so many areas of expertise, mechanical, electronic/electrical, and programming that it can be a formidable hurdle to just get started. But oh, the satisfaction when you succeed!

My first question involves one of the highest hurdles to get over.

Q. I am sure you have heard this a million times before. I'm new to robotics and I don't know how to attach wheels to my motors. Can you help me?

— Clueless Mover

A. Yes, I have heard this one before. I have solved this problem in a number of ways over the years, starting with DIY methods that sometimes even worked. My DIY efforts got more sophisticated when I gained access to folks with lathes and mills. My first efforts were matching motors that I found or got from surplus vendors to wheels that I had from RC car racing or — my favorite — LEGO Technic kits. Figure 1 shows my DIY efforts. Sometimes you can just "fake it".

Figure 2 shows me using a REALLY big servo disk. It worked, and if I found some small rubber bands would even get traction! The robotics hobby industry has gotten into the act and creates kits and motor sets now that work for basic needs. Figure 3 shows a hub set from Jameco ( www.jameco.com) that matched some of my commonly found surplus motors. I just had to carefully drill out wheels to use the bolt patterns. The Mark III kit ( www.junun.org/

MarkIII/Store.jsp) created specially molded wheels to match hobby servo shafts for their robot kit (Figure 4). I really like this chassis. It is simple and very usable in lots of robot tasks, including its original purpose — robot mini Sumo.

Other companies also made custom wheels that used servo hubs attached to them; the one I show in Figure 4 came from Budget Robotics (www.budget robotics.com). Solarbotics (www. solarbotics.com) has DC gear motor sets that they matched their own molded wheels to (Figure 5). These motors did not mount easily to established bases, but by using double-sided sticky tape (also called servo tape in the RC hobby), they attach well just about anywhere.

You can get pretty creative with the solutions that I've mentioned so far, but nothing beats a motor/hub/wheel combination that is meant to go together.