My Robot Design

"-Guess Who-"

If you work hard and put lots of dedication into it, the answer is a "maybe", but the most important thing is that you will learn a lot in the process, which is what counts.

Enjoy and have fun

Padu

I'm doing the same thing with Vex. I'm a robonewbie, so I haven't much to offer. I puzzle over how to connect the front wheel to the rest of the chasis, though. I envision something like a trike, with perhaps two horizontally parallel bars extending from the rear chasis to put bearings into that will strongly enough support the front. But exactly how the servo will fit into this, I'm not clear about yet. Above? Connected to what?

Sigh... These sorts of things seem to be my biggest challenge. I wish there were some site which had construction tips for this (and lots of other things I've puzzled out very slowly.)

Hope others will comment on your post since I'm quite interested in the answer to your question.

Ya I was thinking off putting the servo above the wheel like the pic below, so when the servo rotats the wheel turns, If there is someone more expereanced here, Please tell me is this would work. Thanks, Donncha. _____ | | | | --- Servo | | |_____| | | | | / | | \ / |_| \ \ / ------ Wheeele \___/

It might work, try to find wheels that have just the right amount of traction because if you use too much the servos will burn out and it wont turn properly, too little and it wont turn the robot, also dont use a shoping cart desing where the wheel is offset from the center of the rotational axis or when you back up the it wont back up straight. It will have to go in a semi circle to get the wheel orientated properly. Something that I think might work better for you is having the wheels turn in oposite directions or different speeds to turn

I'm a noob to robotics and a thought this would be the easiest way to make my first one, I was going to mount the servo directly over the wheel with it aligned to the center, So all I have to have is one channel for speed and the other for direction. Putting the batteries and stuff at the front to make it front heavy so the front wheel will get a grip.

Thanks alot, Donncha.

Check out Arrick Robotics design in this photo :

use a servo to steer two wheels. JCD

My design is the other way around, this one has the drive in the front and steering in the back , the opposite to my design.

Perhaps f these sites will help. Nothing like looking at different designs to give yourself new ideas:

site also has a Vex specific forum to post to: Good luck !

Here's the problem with this design: If you have two drive wheels driven by a single motor, and one free-wheeling steering motor, the drive wheels will encounter added friction in in turns because one must go slower than the other to follow the turning arc. If you're lucky the wheels will just harmlessly slip, but usually what happens is that the wheels will "chatter" because of the friction between rubber and road.

In a rear-drive car the differences in rear wheel speed is handled by a differential gear; you could make a differential gear for your bot, but it's not all that easy to get something nice. (If you're interested you can check out some of the designs the LEGO people have come up with.) The Arrick robot gets around this by using one driven wheel, and a pair of unpowered streering wheels coupled with a tie rod to the steering servo. It's an excellent design you should study.

If you're planning on powering each drive wheel with a different motor (you mention you have two 9 volt motors, and the steering motor is a servo), then you don't need the steering servo. You steer the vehicle using traditional differential steering, as found on most bots. Differential steering works whether the wheels are in the center or to one end of the robot.

-- Gordon

I just re-read your post and finally noticed 2 things - the "What else will I need" question being most important. For the design you are talking about you would also need these things: - batteries and a holder (of course) - some kind of speed controller - a servo controller (possibly) - some kind of microcontroller ( like a Basic Stamp from Parallax.com ) You might be able to control a couple of servos using just the microcontroller.

The 2nd thing I noticed - only after seeing that Gordon McComb picked up on it - is that you have 2 drive motors, and I would suggest as did he that you use those for steering instead of a servo on a third wheel. There are 2 big advantages to that approach: 1) You don't need the servo controller, necessarily. This also saves weight, and power requirements. 2) By using the 2 drive wheels to steer, you get the robot to move in place should you need to. It could rotate about it's vertical axis in place, most likely. With the servo steering wheel approach, you have to move either forward or backward in order to change orientation.

Well, all of these are just suggestions. Once you do some actual building you learn even more! Have fun ! JCD

I have a bot that uses a variation on this. It uses two large wheels in back, each driven off it's own motor and the front wheel is a simple swiveling caster. It's easy to control by varying the relationship of the drive to the right and left wheel motors, it is very maneuverable.

Good Luck, Bob

Ok I think I will go with the differential system, Yes I have two motors so how would you make that, I will just use the front wheel as a castor for balance, Why would I need a micro-controller?

Thanks alot, D>> Hello,

I forgot to say why, sorry about that. I mentioned a microcontroller because you need something to be used as the brains of your robot. It doesn't *have* to be a microcontroller, I just assumed that was the best solution because I assumed your bot is small - say less than 1 square foot of space to mount various components on.

One alternative - and I have done this for development purposes - is to tether your robot with a cable to a PC and control it directly from your PC instead of using a microcontroller onboard the bot itself. But even so, many speed controllers are designed to work with pulses and/or other signals that are easily downloaded to a microcontroller from a PC.

It all depends on what you want your bot to do. A good start is to just have it follow along a wall using whatever sensors you want to start with. Some bots use "whiskers" to feel along the wall; some use infrared sensors to measure the distance; others use sonar to measure the distance. Once you get comfortable getting your robot to do things like that, you can move on to more complicated tasks such as finding a beacon, navigating with vision, etc.

If you can post some description of what you want your bot to do I am sure people on this newsgroup will be glad to provide more assistance and guidance.

Cheers ! JCD

No, My robot is going to be more of a remote controlled car. Like the things on "Robot Wars" "Battlebots" ect. That's why I was wondering about the micro-controller.

Thanks, Donncha.

You don't *need* a microcontroller if you're using regular DC motors (and not R/C servo motors) for the drives. You can hook up wired switches as a test. This lets you "drive" the robot around the room with only you controlling it. You need double pole, double throw switches with a center off position for this. Use Google to look up how to wire up these kinds of switches to a motor, or look on page 256 of the Second Edition of my book, Robot Builder's Bonanza for a picture.

(Go to Amazon.com here:

the Search Inside This Book link, type in "dpdt" -- no quotes -- as the search string, then find the lnk to page 256.)

When you tired of manual control you can use whatever control circuit you want, which may indeed include a microcontroller. You will, of course, also need a motor driver circuit, which provides the current needed to operate the motors. But worry about that after you get the robot built.

-- Gordon

You might still need one; or you might not. It all depends on exactly what you want the robot to do. I'd say you need to outline that first and then we all can help you more on this newsgroup.

Good luck !

You don't need a micro-controller for the RC car that you mentioned in another post. The micro-switch arrangement mentioned by Gordon will be usable if your vehicle is not too fast. Another way to do this is to use a pair of reversable speed controls for RC cars and an aircraft radio with elevon mixing capability. Another possibility is a dual channel, mixing speed control like the Roboteq one, but it will be more money.

Good Luck, Bob