Robot tank

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c6jones720

Member
Hi Guys,

I though I would share my latest robotics project. Im building a robot tank. I was planning to be able to remotely control the tank either using a normal radio control handset or with a wireless network.

I built a pair of Electronic speed controls for the tank tracks using Picaxe 18 Microcontrollers. The speed controllers take in standard 1-2ms PWM signals and convert them into output PWM drive signals for the motors lasting between 0-18ms. The ESCs turned out better than I was expecting and so I thought I would share the source code with the community in case anyone else wants to do something similar. Next time I would probably use 8-pin picaxes because they are just smaller. i would definatly use picaxes to do PWM motor control again, even though the BASIC interpreter is a bit slow the chips are more than fast enough to do motor control.



I have a picaxe.net server and I was planning to use that as an onboard computer but Im afraid it just isnt man enough for the job. I was planning to use the I2C output from the board to control extra I/O by sending the Picaxe.net server TCP/IP commands but it just didnt work out. - Not a problem Im goign to use a SheevaPlug server to do that job instead..

Heres the source for the motor controllers. This should work with standard radio gear etc:
 

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Andrew Cowan

Senior Member
Very nice!

Questions:
Motors? Batteries? Maximum speed?
Camera specs? Freqency? Wireless output power/range?
Where did you get the tracks? Are they toothed? What keeps them central?
What sensors does it have?

Great project - I would like to see more photos.

Andrew
 
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c6jones720

Member
Thats pretty cool, thats a bit how my project started out.

The tracks are made of rubber car floor mats that I cut down to size and stapled together. You cant easily buy tracks, and if you use belts you need to use the right pulleys etc.


To keep the tracks central (track throwing always used to be a problem) I sandwiched them between two pillars so that they cant slide off. The wheels are from standard radio control racing cars. To maintain the right friction between the wheel and track I used the same rubber floor mat and made it into a tyre on the drive wheel.



The motors are Mabuchi 380s with planetary gearboxes. The gearbox is something crazy like 250:1. They came from cordless drills. From experiments I did before the maximum speed is around 1 metre per second in a straight line.

The battery is a 12v 7AH sealed lead acid battery. This is enough to power the whole system for a while.

As yet there are no sensors on the vehicle.



As for the wireless stuff: the radio equipment is FM running at 40MHz. The netwrok equipment is all standard so that should be 2.4GHz 802.11g stuff. If you look you can see an old fashioned Milford instruments serial servo controller next to my speed controller. I was trying to interface a Picaxe.Net server to it via the server's serial port.

I was expecting to be able to send TCP/IP commands to the Picaxe.Net server and have it output stuff on its I/O ports but the firware is set up so use just use it as a web page server. its a real shame becase The Picaxe.net server could have been used to do some really cool things.
 
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raffi

New Member
SOS. University Students Italy

c7jones720, you just risolved a huge problem for us beginners a group of 5 university students who are trying to build a similar robot. we were wondering, what power did you give to those motors and how did you reduce it, and in what drill did you find those gears :D maybe we can buy and hack them too. Thx alot.
 
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c6jones720

Member
power and motors etc

Hi the motors came from 3v cordless drills. The gearbox is planetary and I think it is something like 250:1 or something very high like that. Im using 12v Lead acid batteries for power but I built my own speed controllers so effectively I can run the motors at any voltage lower than that.
 
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me_is_monkey

New Member
Absolutely awesome work. I'm planning on building some form of RC go-kart driven by a picaxe.
Just a few questions, I see a headlight at the front, how well does that go at night with the camera?
And are those brake lights/indicators i see at the back? Awesome if they are.
 
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Berny

Member
I would REALLy like more information on your speed controllers. I have read about everything I can on MOSFET PWM and STILL can't get it right! I am not about to open that can of worms here again though so if you could post your schematic, that would be GREAT!
 
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