# Linear Motor driver Circuit

Discussion in 'The Projects Forum' started by zohonie, Dec 2, 2010.

1. ### zohonie Thread Starter New Member

Dec 2, 2010
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Hi All,

I'm trying to building a device that would move back and forth with controllable frequency and magnitude. I'm would like to use either a servo or a linear actuator to do this (Firgelli Automations have decent onces). The linear actuators that I looked at so far would move forward if a postive voltage is applied and backward with change in polarity. Since I would like to make my device work for days, I would like to either purchase a circuit or an IC to do the change of polarity for me. I came across a circuit called a H brdige that would do that, but at this point I'm not sure how I can modulate how often the circuit would change polarity. If you know where I can buy such a circuit or if you would like to sugguest a better way to do what I'm trying to do, that would be great!!!

Thank you very much.

2. ### mik3 Senior Member

Feb 4, 2008
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How exactly do you want to control the linear motor?

3. ### zohonie Thread Starter New Member

Dec 2, 2010
10
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what do you mean exactly?

4. ### mik3 Senior Member

Feb 4, 2008
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Remove the word exactly and answer.

I mean what do you want to do with the motor?

5. ### Bernard AAC Fanatic!

Aug 7, 2008
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Motor specs would help in picking an H bridge IC. A 555 timer can control modulation frequency, to drive a toggle flip-flop which controls input polarity to an H bridge. To control travel , vary motor speed by controlling V to h bridge, analog or PWM.

6. ### zohonie Thread Starter New Member

Dec 2, 2010
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the linear motor would be connected to a piston that would move inside of a cylinder to create suction (negative pressure). I hope that helps

7. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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What is the length of travel?

A "threaded rod" type setup, with the piston mounted on the "nut" would work, many DIY lathes use this approach for X/Y/Z movement.

What force does the piston need to push or pull against in each direction?

8. ### zohonie Thread Starter New Member

Dec 2, 2010
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the lenght of travel is will vary from 1-4 cm. The force is also very small. I didn't do to much calculations, but i would imagine it being in the range of 5-10 newtons.

I'd like to find something that wouldn't require too much construction from my part, which is why i think the linear motor (actuator) is the way to go. what do you think?

I was also thinking about some sort of pulsed vacuum generator, but I can't find anything of use so far.

9. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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How much vacuum do you need to create?

What size enclosure will be evacuated and use this to stay at xx bar?

10. ### zohonie Thread Starter New Member

Dec 2, 2010
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I would need to create about 0.196 bar in a 120 ml enclosure. Again, I would need to vary the pressure in a sine wave manner with 200 cycles per minute.

11. ### shortbus AAC Fanatic!

Sep 30, 2009
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Instead of a linear motor could you use a regular motor with a offset crank pin and connecting rod to the piston? Kind of like a tiny engine with a electric motor running at the required RPM,to create the pulse frequency needed. The piston would move in and out of a cylinder creating the vacuum pulses you need, a small valve could be use on the chamber to adjust the vacuum pressure on with out changing the stroke of the crank.

12. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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This would work well. The way a jigsaw blade works, or a car engine piston. This would also give you a better approximation of a sine wave.

13. ### shortbus AAC Fanatic!

Sep 30, 2009
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Maybe a better way instead of using a piston is to connect the motor to a rubber diaphragm sealed to the chamber. When the connecting rod push es the diaphragm in it gives the positive pressure wave. when the con - rod pulls out it gives the negative/vacuum part of the sine wave. The motor speed still controls the frequency.

Using a diaphragm instead of a piston will eliminate the problem of getting the piston to seal in the cylinder.

14. ### Bernard AAC Fanatic!

Aug 7, 2008
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Not listed as a requirement by PO. Use a disc for crank with spaced tapped holes to vary crank throw. Or drive diafram with hi power speaker.

15. ### shortbus AAC Fanatic!

Sep 30, 2009
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Why? One valve to set the '0' level of the pressure/sine wave. then the valve is closed. Then the in - out of the diaphragm would give the high/low pressure of the wave. Without worry of leakage past a piston or wear/scuffing on the cylinder.

Mechanical fuel pumps on cars have used a diaphragm since the beginning of fuel pump use on cars. When used as a pump you need the valves, but not for this.

Apr 20, 2004
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17. ### GetDeviceInfo Senior Member

Jun 7, 2009
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Best suggestion yet, a subwoofer sealed chamber.

18. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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Yes, I just noticed the 200Hz part. A sub is the perfect Linear Actuator for that frequency.

Apr 5, 2008
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Hello,

200 cycles a minute equals 200 / 60 = 3.33333 Hz.

Bertus

20. ### shortbus AAC Fanatic!

Sep 30, 2009
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Plus with a speaker how do you create the vacuum the O/P needs?