Robot Movement

I’ve been thinking about making a robot that moves back and forth. I know robots can do lots of other things, but Im just thinking about translational movement on and x-y plane only. I’ve seen that some robots have 2 wheels sorta sticking out at the bottom that allows them to move.

I’ve been reading up on the internet and I’ve found a bit on different motors. I’ve always assumed that those wheels at the bottom are powered by dc motors. But I’ve seen servo motors attached to wheels. So Im wondering:

  1. Why would you attach servo motor to a wheel?

I have also seen these robots much like the arduino brand robot, which is a disc-like cylinder with 2 wheels on either side. At first I thought this might be unstable or that it required a complex program to make it stay upright by torquing the wheels constantly. I quickly discarded this as it would be power intensive. Then I saw the ball casters.

  1. So Im wondering if I should just use an Arduino robot?

But I just saw that an Arduino Robot runs $159. Then I saw other arduino-like robot platforms for $50 (CanaKit) and $15(EmGreat). The thing is Im not sure what I want to robot to do. I don’t think I want it to push/pull or carry heavy objects (>1 or 2 lbs). I don’t want a life size robot or anything near that size. I know I should decide on that first or at least close in on an idea. But Im thinking I might have cat sized robot to go around the house and do things such as:

  • connect to the internet
  • alert and inform residents
  • maybe carry envelopes or at most a glass
  • maybe push things like clothes or curtains

So Im wondering about these platforms, like the CanaKit one. Not only do I not like the fact its an aluminum body (i think i prefer a plastic one), but the motors look awfully small-weak. It states they are 70cm/s speed motors. That doesn’t tell me much about the torque. And the rpm data is missing.

  1. What should I base my motor requirements on, rpm, speed, torque or a combination? Since most things in life are always a combination of factors, what rpm/torque should I look for in a robot like mine?

Im thinking toy cars don’t go faster than what, 5mph? So something like that. But something tells me that a 5 mph car, which is about 200 cm/s, is what the motor is capable of without obstructions or in certain nice and smooth terrain and without any weight etc and on a flat surface. How should I include the torque in there? I don’t need the robot to go up inclines more than what you would find in a house, so no more than 5 degrees? Maybe 10 on a messed up house :slight_smile:

I found this:

http://www.societyofrobots.com/mechanics_dynamics.shtml

And Im looking for motors with certain RPM & torque specs as suggested in order to use the calculator. I found this one (HOSSEN® 12V 120RPM & 60N-cm Powerful High Torque DC Gear Box Motor Replacement Motor) and I read that it is suggested to use motors with gearboxes.

  1. Is a gearbox-motor something I should consider or is this too advanced for my simple project? If so, this motor doesn’t include a gearbox, does it? It’s name is simply stating that it is a replacement dc motor for a gearbox setup, right?

I plugged in the numbers for my motor and got the attached values, which says that my RMF should be 8.42 but for a motor like the one I mentioned, it has an RMF of 0.868. That kinda sux. So I look for higher RPM motors but I can’t find ones that also have the torque measurement.

  1. Is there a suggested place to buy them at, where I could find one with that RMF? Im guessing Amazon is not the best place.

Or did I miscalculate something and I ended up shooting for too powerful a motor?

Two simple robot setups: