Robotic Arm Ideas

Pyro Project Ideas/Requests
encrypter
Newbie Pyro
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Joined: Sat Dec 01, 2007 6:06 am

Robotic Arm Ideas

Postby encrypter » Sat Dec 01, 2007 6:17 am

Hi There,

I'm a high school student currently taking an advanced Computer Engineering course. For our final project we have to build a robot that is able to follow a black line on a board and be able to pick up a golf ball that is resting on a golf tee with a robotic arm. The arm is to be 'powered' by a DC motor with a high torque, low speed configuration avaliable from Solarbotics in Canada. My robot is going to be controlled by a PIC (model P16F684 programmed in Assembler) with two more DC motors (this time with low torque, high speed) which will be the two wheels for the robot.

My main question is, from your experience building robotic arms, what would be the best type of arm to construct (in terms of length, opening and closing, etc.)? My apologies in advance as I severely lack the experience of building these types of projects

Thanks for all your help. I'm enjoying the projects you post on your site by the way. Keep up the great work!

Kevin
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Joined: Fri Nov 23, 2007 9:06 pm

Postby Kevin » Sat Dec 01, 2007 8:04 pm

I recommend you to use servo or stepper motors to move the arm because you would need a very complex closed loop feedback for your DC motors. :D

About the arms, I don't know but I'm pretty sure Chris would help you :P

ThePyroElectro
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Postby ThePyroElectro » Sat Dec 01, 2007 8:38 pm

Hey encrypter,

I'm glad they offer this kinda stuff in highschool. I woulda killed to take a class dealing
with electronics/robotics while I was in highschool.

To answer your question:

I've used many of solarbotic's dc motors, the ones geared up for high torque
and they've worked very well. The best part about some of their geared dc motors
is that they also make wheels for their unique GM type motors.

As for the arm gripper itsself. You have the advantage of knowing you need to
get a golf ball so you can design the grippers around that fact. Your limitation,
it sounds like, is you have only 1 motor for controlling the grippers.

:arrow: Length
The longer the arm is, the more torque will be necessary to move it and your center
of gravity will be off creating balance issues (especially with mobile robots)
:arrow: Opening and Closing
Again this is where torque comes into the picture. You'll need to make sure that
the grippers are strong enough to hang onto the golf ball. I have no doubt the solarbotics
motors you're using will provide enough for you to hang onto the ball.

So the simple design of a gripper for picking up a golf ball would look like two spoons
moving horizontally towards the ball on the tee. Once the ball is gripped, pressure will have
to be continually applied on both sides. This will hold the ball and you can bring it back
to wherever it needs to go.

Let me know how it goes, or if you have any more questions.
Sounds like a cool project. :o

encrypter
Newbie Pyro
Posts: 3
Joined: Sat Dec 01, 2007 6:06 am

Postby encrypter » Mon Dec 03, 2007 12:56 am

Thanks for the prompt reply. I've visited various hobby shops in my area to get some ideas. One idea that I've thought is pretty neat is I have a toy claw from my childhood that would serve as an excellent clamp for picking up the golf ball off of the golf tee. This claw is 'powered' by means of a steel rod...when the rod is pulled, the claw contracts, and when the rod is released, the claw expands...from this concept I've been wondering if its possible to construct a mechanism, using either the solarbotics motor or the crank-axle gearbox from the Tamiya kit called 'Remote Control Robot Construction Set' from which when the motor is turned backward, the rod would be pulled towards the motor, which would clamp the claw onto the golf ball. Any ideas, or would any parts in particular aid me in my design?

Thanks once again for the help.

ThePyroElectro
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Postby ThePyroElectro » Tue Dec 04, 2007 8:28 am

Hey Encrypter,

:idea: The Tamiya gearbox from the 'Remote Control Robot Construction Set' seems to be
a pretty good solution for the gripper portion to your project.

I'm familiar with the gripper you're talking about and if I remeber correctly you
only have to pull the metal wire about 2'' inorder for it to completely close the
grippers. That means all you need to do is create a proper lever arm to fit onto the
solarbotics motor, if you wanted to use it.

:arrow: One example implementation might look like (forgive the crudeness):

Image
Image

The pictures above show how you could use a lever arm to pull the wire with the
solarbotics motor. The tamiya gearbox set has a similar setup with motor & lever arm.

Again torque is a very important consideration. These motors aren't technically meant
to be towing cables. If my memory serves me correctly this shouldn't be a problem with
the toy gripper you're planning on using, but it remains an important consideration
because the higher the torque your motors are capable, the harder and faster your
robot will be able to grip.

Any questions are welcome. Hope I'm helping :)

encrypter
Newbie Pyro
Posts: 3
Joined: Sat Dec 01, 2007 6:06 am

Postby encrypter » Thu Dec 13, 2007 3:28 am

Thanks for the detailed feedback. I've come up with a proposal to show to my teacher and I'm waiting for his reply. I'll keep you posted :D


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