Let's Make Robots!

Crawler-mounted actuator

Hi people!

 I'm going to build my first robot and i'd like to mount it with tracks. Can you advise me which type of motor is more suitable. In addition, I thought about electric motor but there are also alot of types: servomotor, step motor, induction motor... if you will refer to some articles i will be very obliged.



ps: sorry for my clumsy english =) 

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They move slow enough that the robot won't go nuts but fast enough to where it will move at a decent speed.

And how about the speed controlling on this motor? Has it third data bus or i should just control the voltage?

You should just control the voltage using PWM. Optionally you could get a motor controller to do the low-level handling of the motor and then just talk to the motor controller using serial communication.

- Jimmy

All depends.

How big will it be? 

How fast do you want it to go?

What weight will it carry?

What type of ground will it cover?

For example, I can highly recommend that you buy a secondhand 250cc quadbike, replace the handlebars with an industrial servo, use a solenoid to select the gears and a torquemotor (perhaps with LVDT feedback) to operate the throttle.

...but that's probably not what you were asking...

Seriously, though, the answer "just PWM" is probably not a lot of good to a fist timer, either. I can highly recommend servo motors for a first robot. Several reasons: you don't need to worry about power control, 'cos they take their drive signal straight off the microcontroller and you get a motor and gearbox for $10. Servos reduce the total electronics and mechanics you need to do.

BUT the cheaper ones don't have very good bearings, they don't go very fast (30RPM would be typical) and they're not massively powerful. (They're quite powerful for their weight.) If you want to operate them in continuous rotation mode, you will need to modify them slightly. (Does anyone know if "modified" servos can be bought off the shelf?) The procedure is all over the net.

Thanks for you answer!

I also thought about servos but (you are right)  I'm daunted with their power...

So, the measurement of my robot is about 15-25cm for lenght (the lenght of a track) and 7-10cm for width. The weight I think will not be more than 1kg. I had no thought about speed, because it isn't the main aim of my project... And that's why I just want it to move.

How do you think, if I'll place two servos (one for a track) and I'll control the rotation angle by moving slowly one servo? will this construction work?

I thought you'd have been more impressed with a 250cc 2-stroke petro engine. That's what I'll be using next.

So, you DO want the servos modified for CONTINUOUS rotation? It's easy enough to do. There are loads of examples on the net. My advice is to go with the one where the variable potentiometer is foreshortened, NOT the one were the VR ir replaced by a pair of resistors. It's surprisingly difficult to find a pair of equally matched resistors. Ask me if you get stuck.

Here's one I prepared earlier. Rubber tracks. Gear ratio from servo head to weels is 1:1.

That should give you an idea of the speed.It's got plenty of torque to carry itself aroud on. The second clip shows that it can lift itself vertical up a wall.

I have a Mark II, which has a 4:1 gear ratio. i.e. it should go 4 times faster with only 1/4 of the power. Now, here's the danger of gearing: It does go slightly faster in a straight line, BUT it turned very very slowly due to the reduced power.

My best guess would be that 1kg would be your absolute upper weight bracket. This little beggar weighs 520g.

Just for info (without the radio gear) it cost about $35.

...which answers your second question. Yes. Tracks. One oging forward, the other going backward will cause a tank to turn on a spot.