Let's Make Robots!

Robot-builders FAQ by Grog

If I want to make my first robot, where do I start?

Your in luck, a wonderful walk-through on how to create your first baby robot is right  here!

 Why does my robots wheels spin until I put it on the floor, then it won't move?

Your motor probably does not have enough torque. Some motors are designed to spin very fast but not have very much power when spinning slowly. In fact most motors need gears to slow them down and provide more power at lower speeds. Gearhead assemblies are a bunch of gears which can be attached to a motor to increase torque and take that wimpy fast motor into a slow muscle motor.

Motor without gearhead, a wimpy motor.

Motor without gearhead, a wimpy motor.
Motor with gearhead, a hefty motor!

Motor with gearhead, a hefty motor!

Another problem might be the amount of current to your motor.

 What is this voltage, current, and resistance I keep hearing about?

The holy trinity of electricity. Although, many people have various ways of visualizing electricity I usually think about it as water.

Voltage - You might think of it as electrical pressure similar to water pressure. If you have some water under very high pressure and you spring a leak, the water travels very far. Electricity under very high pressure will a longer spark. Lightning is an example of electricity under VERY high pressure.

Current - if voltage is pressure in a water system, current would be equivalent to the amount of water moving in a system. For example the amount of water moving through a garden hose is small compared to the amount of water moving through a giant aqueduct. What would be more capable of doing work?

Resistance - you can think of resistance as a crimp in the hose, or something more useful like a water wheel. The fewer crimps you have in the host he more current will flow through it. If there are more crimps the water pressure will increase. Yes, you guessed it. All three of these things are related to one another. And if your into formulas here it is I = V/R or Current = Voltage/Resistance.

Reference -

 

 What should I use for robot brains?

Micro-controllers seem to be very popular in robots. There are many types and many have strong opinions on which are the best. Generally speaking, I would recommend the beginner start with an Arduino or PicAxe. It seems that both these controllers are well documented and can do a lot for being so inexpensive. I personally have not worked with one yet, although it is on my todo list, so you may want to seek more advice or do more research.

Arduino

Arduino
PicAxe

PicAxe

 How should my robot move? Or how many wheels should my robot have?

How fun it is to get your first robot to move! Nothing is quite like the experience of watching a new creation you invented move about. But before this happens you need to decide how your bot should move. The best design for a new robot builder is the two wheeled platform, with a swivel caster or skid. It requires the minimal amount of motors and actuators, only two! Steering is preformed just by changing the speed of the motors.

Simple 2 wheel platform with caster wheel. Both motors going forward will make the robot move forward.

Simple 2 wheel platform with caster wheel. Both motors going forward will make the robot move forward.
Motor 1 goes forward the robot makes a right turn.

Motor 1 goes forward the robot makes a right turn.
Motor 2 goes forward the robot makes left turn.

Motor 2 goes forward the robot makes left turn.
Both motors going backwards makes the robot go backwards.

Both motors going backwards makes the robot go backwards.

 How does the robot make the motors move?

Micro-controller or micro-computers have outputs which typically can not drive motors, or do very much work. However, there are circuits which can drive large motors or switch large amount of electricity. An H-Bridge is a common circuit design, which can be used to move a large DC motor forwards and backwards. They can be very simple and use a couple of relays or transistors. They can also be very elaborate and provide circuit protection, prevent shoot-through, and Pulse Width Modulation speed control. MOSFETS, transistors, and relays can also be used to control all sorts of large actuators.

 Why do my servos jitter?

This can happen when the micro-controller gets busy doing some other task. Frits has some debugging techniques here.

If you are using a PicAxe, some of its recent software has a bug, details here.

Can my robot find fires?  Can my robot follow me using Ifrared Sensor? 

Check out Passive Infrared Sensor PIR or Thermopile array sensors.  Here is a project using a Thremopile array sensor.

Can my robot track me with a PIR (Passive Infrared Sensor)?

No, tracking is a noble thing for a robot to do, however, it is not trivial to implement.  PIRs can only detect changes of infrared.  When the robot moves all infrared sources will be moving, making it impossible to track.  There are a variety of other sensors which might help you with this task - for example Thermopile array sensors , cameras, or laser thermometers.

Please send me additional questions you see repeated on the site

Hopefully, we can add to this as a common reference to those pesky recurring questions. Thanks, GroG