I intend to build a ROBOT car as a hobby project.

The car will be controlled by a small on-board computer and (homegrown) artificial intelligence software.
Web cameras (and possibly other sensors) will provide the computer with information by which to navigate.
Think of the rovers used in the Mars expeditions - it's kind of the same principle...


The requirements of the car is that it should be :

- Able to carry a combined bulk of about 25 lbs (12 kg) (frame, motors, batteries, computer, camera, etc)

- Able to move at a stable very slow speeds (maybe as little as 1 inch pr second) for an extended period (30 min+)

- Able to move at normal walking speed

- Able to move in reverse

- Using 4 electro motors for locomotion (1 for each of 4 wheels, providing on-the-spot turning by running motors on one side forward and the other reverse)

- Using electronic speed controller (ECS) (which will be controlled from the computer)

- Using relatively cheap components (I'm a student!)


Unfortunately I am completely new to electronics and motors (being a computer programming student), so I could use some advice from someone more into this field.


I wonder what I should look (out) for when choosing equipment:


Motors:

What should I look for when selecting the 4 motors for this car ?

Should I connect the wheels directly to the motor, or use belts/cogwhees/drivechains?

Suggestion for specific motor make/model?


Electronic speed control:

What specifications should the ECS meet for handling those 4 motors ?

Do I need more than 1 "dual" speed controller for handling 4 motors?
The 2 motors on each side motors will always be moving at the same speed/direction.
Does that have any relevance for the ECS?
Can I somehow combine those, so the ECS sees each side as one motor?
(As hinted at, I'm a complete newbie with electronics...)

The ECS will be connected to a computer interface card which normally accepts servo connector plugs (3 pins).
Do ECS have similar 3-pin connectors attaced?

Suggestion for specific ECS make/model ?


Any help/suggestion/comment would be very much appreciated!


- Keops

You'll need to gear your motors down, so you can't attach them directly to the wheels.

Why not just buy a Radio Shack robot kit for 229?

I'd rather think of the Darpa Grand Challenge since they at least got 7 miles in 2004 and that is for "autonomous robotic ground vehicles." I believe the prize amount was also doubled to $2M.

http://www.darpa.mil/grandchallenge/index.html

Don't Laugh [X(]!

How about the LEGO Mindstorms Robotics Invention System?
http://shop.lego.com/product.asp?p=3804&cn=55&d=13&t=5
You'll need more motors and sensors to create what you want.

There is a news group Lugnet with all sorts of threads on robotics (RCX)
http://news.lugnet.com/robotics/

This stuff is pretty wild [8D]. I got two set and have used it on different applications like DCC for my LEGO Train sets. Using DCC decoders from other manufacture. The DCC program was download from Mark R.
http://news.lugnet.com/robotics/rcx/?n=2080

Now back to RC stuff !
I will be setting up my LEGO RCX to trap the top speed of my car, once I have time to program it and make the light senors, I'll be set. My car was clocked already at the track, but I want my own speed trap .

you will need high torque motors, better off using a chain or direct drive to the wheels. I recomend using a chain drive if you need it, a chain drive will be better suited due to the lower speeds, and it will be more reliable than belt.

I would recomend motors that have about 15000RPM and alot of torque down low. you might want 12v motors because you could just get a 12v battery or twin 7.2volt packs depending on how big you want to make this thing?

For robot parts check out http://www.robotzone.com and for cheap geared motor drive units check out http://www.robotcombat.com . I bought two wheelchair drive motors on ebay yesterday for $40. They're 110rpm 13amp 24v units. A dual channel speed control from http://www.vantec.com can drive them. They have serial PC interfaces that you can use to drive servos (or speed controls) from a PC. Good luck writing the application, you'll make millions if you can win DARPA!
-Tom

Thanks for great answers!
I'll definately check out the sugestions and links.

Question :
Is it possible to hook up 2 identical motors to 1 speed controller?
If so - serial or parallell setup? (Not PC connector related.)

Any suggestion for specific makes/models of "budget" motors with low torque?
[EDIT: I actually meant HIGH torque here!]

BTW:
I'm definately not going to compete in Darpa Challenge.
Though I do hope to create a fully autonomous vehicle that will be able to perform simple tasks, like "Search this floor for a red ball, and transmit it's location and photo."


- Keops

Yes, it is possible to hook up two identical motors to one controller, but are you thinking about getting double power or getting steering? For double power hook them up in series. For steering you need a dual controller with two separate amplifiers. Vantec has this dual channel business down pat, their controllers have a built-in mixer, with exponential on the steering, adjustable everything, limit switch connectors if desired. There's a lot of options on one of their controllers.

Why do you want low torque from a budget motor? High torque is possible! A good budget motor and gearbox combo is a windshield wiper motor. These can be had from junkyards sometimes by the pound at the U-Pull-it places.

I actually meant high torque...

The "controlling 2 motors with 1 (non-dual) ESC" business is for steering.

If I use 4 wheel power I don't want to use 4 ESC (or 2 dual).

But another perhaps better solution might be to use a chain drive, with 1 motor + 2 wheels on the same chain on each side.

I would guess that setup would be cheaper?


- Keops

Using 4 geared motors is commonly done on one dual ESC. Wire the motors in series so that they share the load. Remember that when you do this you have to double the battery voltage. So two 12v motors will need 24v to drive them, so two 12v gel cells will be required. This will drive all four motors ok because a dual ESC handles each side independently. Check out Vantec's dual ESC's and for cheap motors look up robotcombat.com's AME motor series at http://www.robotcombat.com/marketplace_motors_ame.html . A junkyard will have the cheapest wiper motors. You want about 125rpm as the final drive speed.
There's a great link on building a robot at http://www.coolrobots.com/builders/topframe.html . This is Christian Carlberg's site. He built Minion which was a champion battlebot on TV's Battlebots for a while. Man I really loved watching that bad boy go. Check out the motors in that thing! His main page is http://www.coolrobots.com/ .
Try putting robot parts into google and you'll kill a few hours easily.

Thanks again for great advice, wingspan99!

An alternative to using 1 motor pr wheel might be to instead use 1 motor pr side, and connect a chain to 1 motor and 2 wheels.
That ought to give exactly the same behaviour.

( M = motor , W = wheel , lines = chain )

I quess that would be a both cheaper and lighter setup ?
(2 bigger motors + chain < 4 smaller motors + 1 extra 12V battery ?)

But it does of course require some more mechanical tinkering.

Would the ESC requirements be the same for both alternatives (provided combined motor power is the same)?

What setup would you choose?


- Keops

Well for what you want to do the chain drives would probably work. They're not as tough as four motors. I would use four motors. The chain drive sounds cheaper but if you buy smaller motor/gearboxes you can eliminate two pillowboxes, an axle, four sprockets, two chains, and a lot of adjusting. It leaves more room inside. I kinda like RC car steering though. It's more accurate on the long straight runs. One of the problems of skid steering is getting precisely the angle you want. Some guys put a heading hold gyro in the circuit and let the gyro manage the skid steering. The RC car style steering isn't as maneuverable but it will carve a turn nicer. Maybe a combination of the two would be best by steering the front motor mounts with a servo and y- connect it to the ail channel external to the dual ESC, installed after a heading hold gyro. When you want skid steering it would still be available. (That smoke is my lightbulb going off). Hey I like that, I might use that on my next project. Well I'm no expert in robots, but I stayed at a Holiday Inn last night I did make a few RC lawnmowers which you can see at http://www.hoverbatics.com/200MPH
-Tom
-Tom

out of curiousity, what tools, materials and resources do you have access to?

I have a really pitiful collection of tools considering what I want to do. Ryobi Bandsaw (crap), good Delta disc/belt sander, good grinder, good drill press, awful stick welder, cheap hand tools, some air tools like die grinder, cutoff tool, etc. I am shopping for a mini lathe, a mini mill, and a Mig/flux welder. Those three things would quadruple my overall capabilities as a builder, which would still be pitiful.
-Tom