basic components of a bot

[ElectronikCid122]

well i gave up io cant find a bot so im gonna make one. i have a bread board but its kinda big(thts ok) like 6 by4. i can solder. i hve capacators resistors diodes basic stuff like thtt some ic chips which i dont know what do. so what would i need to make a bot. can you list some components i will need and some links to sites where i can get this stuff?
thanks

 

[dknguyen]

A gearmotor is probably the hardest thing to find- and the way to mount it onto the wheels. Maybe you could modify RC servos for continuous rotation. YOu can get them at your local RC hobby store.

 

[evandude]

Well, a basic mobile robot platform sounds like a good way to play with electronics, however you can't do much until you get motor drivers sorted out. If your knowledge is limited to some basic discrete components then building them could be difficult, though with the designs available online it is still possible. But, it might not be a bad idea to look for some commercially available motor driver boards to reduce the number of variables you have to deal with before you can get the thing moving.

 

[dknguyen]

Yeah, it's a bit pointless to build a motor driver board until you can program something like a PIC to test it with. (Servo motors have these in them already by the way which makes it really nice for small robots). But it's quite nice to build your own motor driver eventually.

 

[ElectronikCid122]

well i hve servos reciever mechanical speed control from my kit rc cars. the radio is a futaba made for rc cars. well i would want my bot to work on tracks so i have it sorted out. it will have 2 motors. one on the bottom left corner attached to a driving wheel. then the second motor will be on the upper right hand corner also attached to a driving wheel. and when u want to go for ward both will run as 1. but when you want to go left or right one motor will run and turn the bot. kinda like a real tank.

 

[dknguyen]

Wait, if you have an RC car why don't you just retrofit that with a control board? I was thinking about suggesting that to you, except RC trucks are like $200+ with an average cost of $500. Just replace the radio receiver with a control board that takes in sensor readings and outputs PWM pulses to the RC servos to control everything else. If it's a nitro, then remember to make the servo throttle move in bursts so it doesn't get too fast since you probably won't be starting out with any speed sensing. if it's electric, it shouldn't be a problem to take control of the speed controller. If it's a RC car, it's a bit harder than if it's an RC truck, since those tend to travel slower and are less terrain fussy in the first place.

Tracks are a pain...and expensive. But it's entirely possible on robot less than 8" in size since there are appropriate track kits out there. They are also less efficient than wheels during turning- remember that.

Having a differentially steered robot is nice, but it still doesn't beat having a full-blown suspension platform- even if you have to use ackerman steering! It would be an outdoor robot though due to speed and lack of zero-degree turning radius. Seriously, the chassis and suspension on a RC truck is far superior to almost anything else you can get, short of the Mars Rover Rocker-Bogey suspension or parts-intensive tank treads with individually suspended idlers (which almost no hobby robot with tracks will have). It's even better if you hack the suspension to get rid of the ackerman steering and make it differentially steered (or even with individually turnable wheels so you don't have to skid when turning on the spot). Well there are two-wheeled balancers, legs, snakes and fliers, but none of those have as much overall robustness+efficiency as wheels (or tracks)...right now anyways... Two wheeled bots are the excemption, but only on fairly flat terrain and they have coolness factor. 3 or more wheels is only cool if you have suspension, hehe. The other methods are are energy/weight intensive (legs) or restrictive (fliers). Snakes are neat, but get expensive fast (but the cost levels out if you go all out due to repeating segments).

 

[ElectronikCid122]

the truck is 2wd electric. so ur saying i should remove the reviever and put in a control board. can u hook up the motor and steering and stuff like that to it. how much would a control board cost??

 

[dknguyen]

A control board is little more than the printed circuit board with a microcontroller like a PIC, AVR, PICAXE, or BASIC stamp on it (similar to the one on the BOE-bot). You could buy one (they range from about $60 I think to many many many hundreds lol). You can also build one. You'll need at least a breadboard, a voltage regulator chip, some capacitors, and a microcontroller.

-a microcontroller like a PIC or AVR straight from the semiconductor company requires a programmer which will cost a bit more than the other equipment listed. A programmer is a chunk of hardware (sometimes built onto the circuit board) that sits between the PC and the microcontroller and lets the computer interface with and program the microcontroller
-if you go for a PICAXE, Basic Stamp, OOPic, Basic Atom, or something else like that all the programming stuff is take care of (all of these have their own development boards you can just buy)

So to the car...
-Steering is done through a servo motor
-if it's electric then that means there is an electric motor behind the drive wheels. There's probably "some other" piece of electronics inside that sits between the motor and receiver. This is the motor driver and takes control signals from the receiver and outputs the large higher voltage, higher current to the motor to drive it (remember a microchip or receiver can't do this which is why this speed controller or motor driver is there).

The bare bones says that you plug the proper power up to the servo and motor driver and then run all the PWM pulse lines to pins on the microcontroller that are either PWM or output compare (this function lets you output a PWM signal). So then the microcontroller basically looks like a radio receiver to the servo and motor driver. From there the microcontroller can read in sensor inputs or whatever and send the appropriate signals to the two motors. You also need at least one sensor to avoid things or stop when it hits. If it's electric you can probably control the speed to be very low. It depends on your motor driver which you should know a thing or two about. The higher your minimum speed the longer range the sensor has to be since if you hit things at top speed...

 

[ElectronikCid122]

yes there is a piece between the reviever and the motor. its a mechanical speed control when you give the truck throttle it goes to the reviever and the mechanical speed control gives the proper voltage to drive the motor.

 

[dknguyen]

1. What voltage does your car run at?
2. Is it a brushed motor? Please tell me it's a brushed motor. What voltage are the truck batteries?
3. What model is your truck?
4. What are the truck's dimensions?

BASIC STAMP 2 - Board of Education (from the BOE-Bot kit):
USB- http://www.parallax.com/detail.asp?product_id=28850
Serial- http://www.parallax.com/detail.asp?product_id=28150
Others- **broken link removed**

OOPic/OOPic-R (this is the one I had offered to you):
http://www.oopic.com/
It can come as a chip but you'd be stupid not to get it as a development board which it almost always is anyways.

PICAXE (I think this is the most inexpensive)-

This seems to be the only US and on Canadian distributor for PICAXE.
US- http://world-educational-services.net/cart/index.php main_page=index&cPath=7
Canada- www.hvwtech.com

I think you'll be pleasantly suprised by the cost of the PICAXE starter kits.

EDIT:
**broken link removed**

So that's a mechanical speed control? I always assumed every truck used an electronic speed control, but then I guess "electronic" is there for a advertisement purposes for a reason right?

So yeah, this is the exact same thing then as if it was a nitro truck. Just imagine the mech speed control is the throttle of a Nitro engine. Both are controlled by a servo which you plug into your control board. The more the servo moves a certain way, the faster it goes. I'd really get that replaced with an electronic speed control though...but that's is very obviously biased. Depending on the current you could build your own (now or eventually), but you probably have your hands full right now. You could also buy one if you know the current that the motors can draw (from a RC store if you want to pay big money and interface it just like a servo motor or cheaper from a robot store, as long as the current isn't too high and you can do some neat "computer-things" with it .

WIth the mechanical speed control, you plug all servos into to the controlboard to PWM-capable pins on the uC (microcontroller, u is the latin letter for micro like micrometers). if it's an electronic speed control it may be PWM or serial or something else, either way it all plugs to the right pin on the microcontroller.

Have you seen this thing?
http://www.geology.smu.edu/~dpa-www/robo/jbot/
I wanna build one like it, hehe...after I finish my current horribly overbudget robot.

 

[ElectronikCid122]

umm im not exactly sure on tyhe volts i think its around 6-14 volts. the motor has brushes. its a stock 540 tamiya motor. tht robot is sweet. i would like to makr my rc car similar to that.my truck is the old version of the midnight pumpkin. the dimensions are16 1/2 by 7 by 9 1/2. i saw something on the web site i want to get. the tank bot on http://www.oopic.com/
wat would i need to get a project like thtt going???

 

[dknguyen]

The voltage is whatever battery you plug into the car. 12V sounds about right.

The tank robot is from here (if you clicked on the picture on the OOPic site):
**broken link removed**

There is also this one:
**broken link removed**

Just buy it if you want tracks- don't try to make them on your own. Not yet anyway. You'd basically need the chassis, motors, control board, and a sensor or two. Probably a BOE board or a PICAXE starter kit.

 

[ElectronikCid122]

actually my dad said he mite let me buy that sumo bot **broken link removed**

 

[House0Fwax]

Try adapting what you have got with something;
like this ---> http://www.geocities.com/tjacodesign/cerberes/cerberes.html
Tjaco's design graveyard