Tread Robot

[Jaryd]

I want to build a robot with treads(tracks) on it(like a tank)But... i have 2 questions.

1. Where can i buy a good set of treads(tracks) for cheap...im 15 and cant afford 2 tracks for $40 each and how big should they be?

2.Should i use 2 servos or should i used 2 motors?

Thankyou

[nottoooily]

A mechanic can probably give you old cam belts for free. They will have been removed for preventative maintenance even if they still have plenty of life left.

Another way I did once was bicycle inner tubes. You can cut a strip to length and glue the ends together with puncture repair glue. Do a tapered overlap to get a large glued area without any lump in the thickness.

[SmAsH]

I would love to help you but... I have two questions.
1. What size do you want the robot to be?
2. What speed, torque and price range are you looking for, remember motors will need drivers.?

[Joker94]

well here are some good tank treads

http://www.sparkfun.com/commerce/product_info.php?products_id=321

As for motors or servos, servos dont need external drivers and i know you can add encoders to them as i currently am working on servo encoders. Motors are easier to add encoders to and some even come with encoders but like smash  said you do need the extra circuitry that will be a tad expensive if you get a pre made circuit. although you can build controllers yourself for a few bucks each, always a path for a tight budget.

[Jaryd]

Ok...thankyou all. 1. I have not yet determined a size but anything will work probably 2-4inches wide 3-6 inches long weight undetermined... I was planning on building my own micro controller by following the $50 robot tutorial and then just using 2 modifies hs311 servos so... Would that work?? Thanks                                                                                                                                   

[RoboChan]

Why tracks? they are cool sure but why spend money on tracks if you do not need them?

[little-c]

cheep rc tank? if your willing to hack it properly, you can take the motor controler from it. might require hacking the pcb and working out where to bypass the existing curcit.

[Jaryd]

well... if u looked at that link(thanks to joker94) they are only like $8 so i will just use those... now im wondering if the microcontroller used in the $50 robot tutorial and 2 hs 311 modified servos will work?

[waltr]

I think the problem with using modified servos with that tread kit is connecting the servos to the tread wheels. Or is this easier than I think?
 It seems that the  Dual gearbox from Tamiya is designed to be used with that tread kit.
http://www.sparkfun.com/commerce/product_info.php?products_id=319

This will require a dual H-bridge motor driver but there are a few available.
http://www.sparkfun.com/commerce/categories.php?c=179

And I believe that there is code for the microcontroller used in the $50 robot to run a dual motor controller.
Anyone know?

Anyone know what the motor stall current is for the Tamiya gearbox?

[Jaryd]

Ok... before i order anything will the Dual gearbox and dual H-bridge motor driver plan work?

Thanks Waltr

[vinito]

This is maybe a longshot, but...
I bought a toy tank at a thrift store the other day for $5.
The circuitry inside it was fried chicken, but that was crap anyway. It had two motors with gear reduction on each. It's an inexpensive plastic gear box, but it looks just like several of the ones I see for sale on robotic sites.
The treads and motors and gearboxes work fine, which is what I wanted anyway. Removing a few screws allows the top to pop off. Tadaa! Instant and inexpensive track robot chassis. Pretty good sized rectangular space for electronics and batteries between the tracks.

OK I'm done gloating. But the point is, you may very well find some suitable robot chassis and other parts at a local thrift store. Now that I'm into robots, I never skip the toy aisle at regular stores either, but thrift stores are great places to rummage through for robot parts and ideas. Give that a shot.

I plan to dream up some kind of H-bridge driver of my own to drive this thing. You might google and do a little reading about H-bridge drivers. It's a pretty simple and cheap way to drive motors. Here's a couple prett good links about them (Link) and (Link)

[Jaryd]

Nice... thanks!!

[waltr]

An H-bridge will allow full speed and directional control but if you are just starting out, want to keep it simple as you learn and don't have much money then consider just an on/off control on each motor. With both motors on it goes forward, With only one motor on it turns. That's about all that is really needed and can be done with a couple of relays or transistors controlled from a microcontroller.
You may be surprised at just how little is needed.
This way you have a working robot while you build your own H-bridge which is a worth while endeavor.

Have fun.

[Jaryd]

ok thanks Waltr...last question... will the $50 microcontroller work for this project or will i nee a different one??

[Joker94]

yes the $50 robot controller will work for what you want it to do. the $5o robot board can do alot of things. The main problem is when you run out of space or i/o pins with a bigger project.

[Jaryd]

Ok... Thankyou all