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Author Topic: $50 Robot on Meccano chassis  (Read 2902 times)

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Offline peethornTopic starter

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$50 Robot on Meccano chassis
« on: October 08, 2009, 03:46:54 PM »
Hi All

I am very new to robotics and electronics. I have been spending a lot of time reading up on the various subject areas.
I am from South Africa.
I wanted to build the $50 robot as my first robot. I ordered the necessary parts from a local supplier (Our exchange rate to the dollar is not too great)
While I wait for the order to arrive I decided to start building my chassis. I appropriated one of my son's Meccano sets as I thought this would make a fairly sturdy base.
I am however struggling to find a local supplier of servo motors. My plan was to let the motor drive on the geared rim of the Meccano wheels.
The question is: Will a servo motor have enough rpm if I drive the wheels in this way? The rim gear on the wheel has 57 teeth.
Would it be an option to use normal dc motors to drive the wheels in this way? The prototyping board I ordered is big enough that I can build two H bridges on it as well.

Any input would be appreciated.

Peet

PS. Here is a photo of the chassis:
« Last Edit: October 08, 2009, 04:03:07 PM by peethorn »

Offline blackbeard

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Re: $50 Robot on Meccano chassis
« Reply #1 on: October 08, 2009, 04:33:57 PM »
Dealextreme is has servos. they're pretty cheep too at $5 shipped each. you could always use DC gear motors but that would involve changing the code and pinout as well as build an H bridge unless you want to add a motor controller.
"sure, you can test your combat robot on kittens... But all your going to do is make kitten juice"

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Next step: Give them vaginas

Offline peethornTopic starter

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Re: $50 Robot on Meccano chassis
« Reply #2 on: October 09, 2009, 01:27:41 AM »
Thanks, If I decide to use servos will the bot not be terribly slow?
Is there a lot that needs to change in the code if I use dc motors?
I am in learning mode, so I would like to build the H bridges myself to learn how they work.
I guess the other option would be to take the Meccano wheels off their axles and attach them directly to the servos.

I was planning to put a battery holder in the gey box area near the castor wheel.
Will a single holder with 4 AA batteries be enough to drive the controller and the two motors?

Pete

Offline SmAsH

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Re: $50 Robot on Meccano chassis
« Reply #3 on: October 09, 2009, 01:45:20 AM »
servos aren't too slow, but they do vary quite a bit.
You don't need to change a great deal of code, but it is harder to do if you are new to robotics.
A H-bridge tutorial can be found here: http://www.societyofrobots.com/schematics_h-bridgedes.shtml
6v may not be enough to drive the 7805, have you considered using two packs?
Howdy

Offline Soeren

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Re: $50 Robot on Meccano chassis
« Reply #4 on: October 09, 2009, 02:08:57 AM »
Hi,

If I decide to use servos will the bot not be terribly slow?
Excruciatingly so!
Or to put it another way, you're gonna time it's speed with a tear-off calender ;D

The servo has too high a gearing. You could hack the servo, but the motor in a servo is ridiculously small, so my vote is for a DC motor.
The easy route if all else fails is to get one of the cheap servos AND a DC motor from DealExtreme or a similar place and use the DC motor instead of the one in the servo, but keeping the electronics (perhaps boosting it a bit if needed.
That way you can use the code directly.

For your trike, I would use this to drive the front wheel, an unmodified servo to turn the front fork, and just letting the rear wheels trail behind.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline peethornTopic starter

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Re: $50 Robot on Meccano chassis
« Reply #5 on: October 09, 2009, 02:34:30 AM »
Thanks for the feedback, guys.

The idea was to have differential drive. I think I will go with DC motors then.
I am new to robotics but I not new to programming.
If I get stuck with the code I will ask again.

Now just to get all the goodies.

Offline waltr

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Re: $50 Robot on Meccano chassis
« Reply #6 on: October 09, 2009, 08:30:21 AM »
Servos work well for differential wheel drive but the wheels need to be connected directly to the servo outputs.
There is lots of information on how to do this.

 


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