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Author Topic: FWD/REV Actuator using Hobby Grade RC Car Motor and Speed Control. Help!  (Read 1441 times)

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Offline jim5192Topic starter

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I have a couple quick questions that shouldn't be too difficult for someone.

Background: I'm trying to make a double inverted pendulum for a senior project (electrical engineering). I'm still in the design phase, but I want to make sure I know what to get before I got out and buy tons of parts. Basically, I need to construct something like this:

http://hackaday.com/2010/11/27/balancing-inverted-pendulums/

I have yet to decide whether I want to make the base's actuator along a rail, or put the double pendulum on a car, and just have the car zoom forward and backward. Regardless, I need a very strong actuator with reasonable speed and high torque.

So far, the best thing I've found as far as actuators go is an RC car hobby grade motor and ESC:

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXMUN9&P=0
and
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXAXT8&P=M

I have an arduino mega 2560 that I'm planning on using as the DSP controller. It has an onboard ADC, and outputs PWM which I was hoping to use to control the actuator.

 At this point, I have one major question and a couple small ones.

Major Question: Is there an ESC for a motor of this power type that has equal quality forward AND reverse control? (these esc's are for RC cars...they only need to go reverse at a fraction of the speed they need to go forward. This would be non-ideal for double pendulum control.)

Smaller Question 1) What type of input signals do ESCís need? I have a PWM signal available from the Arduino. Would this work?

Smaller Question 2)  If there is no such actuator system that is both reversible and controllable via PWM, what am I to do to implement this system given that I want to keep costs down?

Thank you so much for your time and words of wisdom!!!!!

"Imagination is more important than knowledge."-Einstein

Offline newInRobotics

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Re: FWD/REV Actuator using Hobby Grade RC Car Motor and Speed Control. Help!
« Reply #1 on: October 20, 2011, 03:47:52 AM »
Nice project to undertake.

It is better to have actuator on a rail as You get zero movement in a perpendicular axis. System gets more stable as it can move only in 2D.

You don't need much torque for this application as balancing does not require lots of force. Favor speed over torque, as short reaction time is a must.

Build a MOSFET H-bridge to keep Your cost down, have same responce speed to both directions and take PWM as an input. Depending on the motor power ESC might get very pricey, where power MOSFETS are cheap. You can also buy 2 pairs of complementary MOSFET packages (Half bridges) to make Your task easier.
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Offline jim5192Topic starter

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Re: FWD/REV Actuator using Hobby Grade RC Car Motor and Speed Control. Help!
« Reply #2 on: October 20, 2011, 05:16:33 PM »
I'll be sure to use this recommendation for the H-bridge build. But I want to make sure I am clear about the double pendulum.

I'm not trying to just keep the double pendulum inverted. I want be able to swing up the pendulum from a hanging state. For this reason I'll be needing reasonable torque, no?

Thanks again.
"Imagination is more important than knowledge."-Einstein

Offline newInRobotics

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Re: FWD/REV Actuator using Hobby Grade RC Car Motor and Speed Control. Help!
« Reply #3 on: October 21, 2011, 12:53:17 AM »
I'm not trying to just keep the double pendulum inverted. I want be able to swing up the pendulum from a hanging state. For this reason I'll be needing reasonable torque, no?
Yes and No  ;D Swinging pendulum to the upright position will require more torque than to just balance it, however most of the "swing-up" force is extracted from moving pendulum itself, hence motor has to add just little power to make pendulum go slightly higher with every swing. Imagine Yourself on a swing, You give initial force to make Yourself swing slightly and from there You add less than initial force to increase motion and even less force to sustain oscillation.

To get torque requirements use length of fully extended pendulum and weight of it (this will give You stall torque of the motor), multiply it by 2 and there You have what to look for.
"Computer games don't affect kids; I mean if Pac-Man affected us as kids, we'd all be running around in darkened rooms, munching magic pills and listening to repetitive electronic music." - Kristian W

Offline jim5192Topic starter

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Re: FWD/REV Actuator using Hobby Grade RC Car Motor and Speed Control. Help!
« Reply #4 on: October 23, 2011, 09:16:24 PM »
Thank you for all of the wonderful advice so far. I believe at this point I have a decent understanding of the programming and electronics involved in this project (aside from some details to deal with later), but I've run into yet another road block.

Basically, where in the world would I get the parts for the actual double pendulum? I don't have any rail and or wagon as seen in this video:

http://hackaday.com/2010/11/27/balancing-inverted-pendulums/

I have only the power of the internet and maybe a few hundred bucks TOPS to spend on everything including the electronics. I have some hobby tools (dremel, pliers, etc.), so modifications, adjustments to hardware is limited but I do not have a workshop at my disposal, so manufacturing parts on my own so to speak isn't really an option. I can buy separate parts, but part must be somewhat pre-manufactured. Any ideas?
"Imagination is more important than knowledge."-Einstein

 


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