Quote:
Originally posted by Replic
My dad has recently become as fascinated with FIRST as I, and we have decided as a father/son project to begin the building of a robot of our own, much smaller of course.
One of the questions I have no answer to yet is- what kind of motor shall I use, and where can I get these motors? Keep in mind, I don't have a budget the size of the FIRST teams.
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My first question is "do you have some electronics experience"? There are ways to build this CHEAPLY if you do.
If you wish to "work at this scale", you basically need four things:
1) A set of motors, on a platform
2) Power
3) Some kind of control system.
3a) Autonomous robots needs a CPU of some kind, and/or some sensors.
3B) Radio control needs both the radio link and some kind of decoder at the receiver side to talk to the high current motor drivers.
4) Some motor driver circuitry that can handle the motor's current needs.
IMHO, the cheapest way to get into this "scale" is the following:
1 - the motors and platform) Find a thrown out Fisher Price or other "kid's riding jeep". The batteries fail all of the time, and you can often get them for FREE. Make sure you get one that uses a PAIR of motors instead of just one. This gives you your platform and a pair of FP motors with gearboxes. If possible, find one that uses a standalone "tube frame" instead of the ones that rely on the plastic body to hold things together. If you can find one with a tube frame, throw away the body and add a simple rectangular board to hold stuff. If you can't, you'll have to cut an odd shaped piece of plywood to conform to the funny shape of the side supports.
Separate the wiring between the motors (they're normally tied together). This gives you two motors for "differential steering". Now replace the front tires with casters from a hardware store and your basic frame is complete.
BTW, I have found this works better if you consider the motor side as now the "front". The "tail" then swings around behind as you drive it, instead of it "brandishing a spear" in front of it as it moves.
2) For power, you can use a standard "maintenance free" car battery (to prevent acid spills). This is cheaper than a gel cell, but it doesn't like to be deep cycled. For a few more dollars you can get a Marine Battery that IS designed for Deep Cycling. You'll need a car styled battery charger for it. You can often find used car battery chargers in the "cheapie" for sale ads in the newspapers.
3a - Control System) Pick up one of several Basic Stamp style micros (such as from Parallax), or a LEGO RCX Mindstorms kit. This gives you a processor. "Nuts and Volts" magazine has a TON of ads for them. You can get into a processor system often for under $100 if you wire up your own board (under $200 if you don't or can't).
3b - Radio Control) If you are NOT going autonomous, there are various ways to create a cheap radio link, including surplus companies or ones like Jameco that have raw transmitter/receiver board pairs that are fairly inexpensive. Which system depends highly on how tightly you wish to control the robot. With straight RC control, you can use off the shelf RC car hardware. If you're commanding a CPU which then commands the power controls, there are inexpensive "remote control" raw transmitter and receiver pairs or TV remote "IR receiver" circuits that can be attached directly to a CPU. Either send "ritual commands" to the CPU to have the robot execute preprogrammed actions.
4 - Motor Power Control Circuits) To drive each motor you'll need either a full H-bridge control, or a single MOSFET circuit with an optional reversing relay. Once you have the first three items dealt with, I can show you how to build this.
BTW... A group I'm with is currently creating a set of VERY inexpensive control circuit PCBs to allow "kid's riding jeep motor hacking" from Stamps, or even an RCX brick! We're hoping to bridge the gap between Lego League and FIRST with them, as well as soon sponsor some offseason contests using them for teams with spare kit parts. If interested, email me after the 2003 build about it.
- Keith