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Old 02-15-07, 08:45 PM   #1
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Does this sound like a promising physics project? *somewhat lengthy*

I need to do an impressive final physics project. This is due in June, so I've got time. But, I do not want to waste it! So, I think I've come up with a possible topic and method. The important thing is that we are testing. It can't just be building something. You've got to be testing for something; the presence of something, the effect of something, etc. Many trials should be run.

So....

The effects of mechanical resonance on the accuracy and repeatability of a stepping motor.
Resonance is a phenomenon which has always intrigued and mystified me, this is a great chance to explore I think.

So basically I will make a linear positioning system, a stage, leadscrew driven and a stepper motor drives the screw. I will make all nuts antibacklash, so mechanical repeatability will be excellent. Since a stepper driven system is usually open loop, the motor is the biggest source of possible error. So, I will use a .0001" dial indicator to make a zero point. Then, I will write a program to drive the motor. The program will last about 15 miniutes, will have sporatic negative and positive accelerations, a little of everything. I will write the program to deliberately target the resonance zones of most stepper motors. Then, finally after 15 minutes of motor rigor, I will have the motor return to the original zero position. This will depress the plunger of the .0001" dial indicator, and the indicator should return right to zero. I will document my findings. I know that when the motor is in it's natural frequency range while operating, it makes noise. I suspect it stalls a tiny bit too, this is a way to find out how much. There is no way to know on the fly unless an encoder was used.

I will try several different motors. Higher end American brands, generic motors, some tiny motors, some large motors. Then I will try once more with a mechanical damper to suppress resonance, recording any improvements. Then once more with super high end stepper drives, which electronically suppress resonance. The first drive is a 50 dollar hobby level drive. The second drive to test is a 550 dollar Pacific Scientific, so it should offer a contrast.

My friend has just shown me a soundcard oscilloscope. You literally use your soundcard for dual channel operation with high frequency capacity. I can make a little circuit to bring down the voltage to appropriate levels. I could record the back EMF of the motor while it resonates, this should also allow me to compare the effects that the dampers have on the natural frequencies of the motor.

My lab report needs to be a good 30 pages, so this should fill it.
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Old 02-15-07, 08:47 PM   #2
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One thing though, I am unsure about what kind of load I should make for the motors. A weight on the linear stage is the idea to make a load.
Should I have a consistent load for all tests? Or a load proportional to the rated torque of the motor? Ie.
Motor twice as powerful = twice the load.
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Old 02-15-07, 08:50 PM   #3
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I'd say proportional load to stay with a consistency in loading.

That way you can come up with a ratio of f(X)/f(X)
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Old 02-15-07, 08:52 PM   #4
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I'd say proportional load to stay with a consistency in loading.

That way you can come up with a ratio of f(X)/f(X)
I agree, so there it is. Load proportional to torque.
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Old 02-15-07, 08:57 PM   #5
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A promising physics project needs to involve projectiles. How about a magnetically propelled missile? Maybe you could figure out how to optimize acceleration for projectiles of different masses.

... or you could go with the less flashy project you thought of.
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Old 02-15-07, 08:58 PM   #6
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lol, some kid wanted to make a rail gun. Frankly though, I don't see much complexity in that. Isn't it just a primitive linear motor?
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Old 02-15-07, 09:01 PM   #7
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Quote:
Originally Posted by phantomcow2
lol, some kid wanted to make a rail gun. Frankly though, I don't see much complexity in that. Isn't it just a primitive linear motor?
The concept is straightforward, but inducing the projectile to reach maximum velocity with minimum power...
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Old 02-15-07, 09:02 PM   #8
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lol, some kid wanted to make a rail gun. Frankly though, I don't see much complexity in that. Isn't it just a primitive linear motor?
It's a linear motor alright! It would be a cool project though. One of the reasons we've never built a military application is because of power supply issues and cycle speed to recharge the system with the current technology. There is a project under consideration by the navy for a railgun project right now though!
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Old 02-15-07, 10:58 PM   #9
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Phantomcow, you go to the craziest high school ever. That project sounds way intense. I'm a college junior in mechanical engineering, and none of my profs have ever had me do a project like that.

As far as the rail gun is concerned, the trick is to apply enough power to get good velocity without welding the projectile to the rails.
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Old 02-15-07, 11:32 PM   #10
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Phantomcow, you go to the craziest high school ever. That project sounds way intense. I'm a college junior in mechanical engineering, and none of my profs have ever had me do a project like that.

As far as the rail gun is concerned, the trick is to apply enough power to get good velocity without welding the projectile to the rails.
He's in an AP class......never would have guessed that, eh?
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Old 02-16-07, 01:53 AM   #11
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Your physics project should be on the discovery of the force that held people to the earth before the discovery of gravity.
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Old 02-16-07, 05:20 AM   #12
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Old 02-16-07, 03:24 PM   #13
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Well, I wish I could do well on the tests in that class . We just had one today.
A problem was something like:
Some tiny piece of paper is hovering in a uniform electric field with a field strength of .26N/C
The paper had a charge of 36mC

Find the mass of the paper. I actually think I got that. I solved for Force using E = F/q
Then made a force balance for my vertical vector. So Fe + Fg = ma, but a = 0, so it's all equal to zero on that side of the equation. Substitute m*g for fg, solve for m.

The one that really killed was where there were four ions (and we were expected to retain all knowledge of chemistry from last year, not good!) placed apart in a rectangle. Find the magnitude and direction of force on one of the protons, find the instantaneous acceleration on that proton, and some stuff I don't even remember. Ugh
I feel like this guy just expects us to know this stuff. He covers the concepts of what is ACTUALLY going on very little, but gets mad if we have anything pertaining to Physics from another source in his classroom.
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Old 02-16-07, 04:01 PM   #14
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Quote:
Originally Posted by phantomcow2
Well, I wish I could do well on the tests in that class . We just had one today.
A problem was something like:
Some tiny piece of paper is hovering in a uniform electric field with a field strength of .26N/C
The paper had a charge of 36mC

Find the mass of the paper. I actually think I got that. I solved for Force using E = F/q
Then made a force balance for my vertical vector. So Fe + Fg = ma, but a = 0, so it's all equal to zero on that side of the equation. Substitute m*g for fg, solve for m.

The one that really killed was where there were four ions (and we were expected to retain all knowledge of chemistry from last year, not good!) placed apart in a rectangle. Find the magnitude and direction of force on one of the protons, find the instantaneous acceleration on that proton, and some stuff I don't even remember. Ugh
I feel like this guy just expects us to know this stuff. He covers the concepts of what is ACTUALLY going on very little, but gets mad if we have anything pertaining to Physics from another source in his classroom.

I've said it before, and I'll say it again - your instructor is Fruit Loops.
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Old 02-16-07, 06:39 PM   #15
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Quote:
Originally Posted by phantomcow2
Well, I wish I could do well on the tests in that class . We just had one today.
A problem was something like:
Some tiny piece of paper is hovering in a uniform electric field with a field strength of .26N/C
The paper had a charge of 36mC

Find the mass of the paper. I actually think I got that. I solved for Force using E = F/q
Then made a force balance for my vertical vector. So Fe + Fg = ma, but a = 0, so it's all equal to zero on that side of the equation. Substitute m*g for fg, solve for m.

The one that really killed was where there were four ions (and we were expected to retain all knowledge of chemistry from last year, not good!) placed apart in a rectangle. Find the magnitude and direction of force on one of the protons, find the instantaneous acceleration on that proton, and some stuff I don't even remember. Ugh
I feel like this guy just expects us to know this stuff. He covers the concepts of what is ACTUALLY going on very little, but gets mad if we have anything pertaining to Physics from another source in his classroom.
Exactly how AP is this AP class?
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Old 02-16-07, 06:51 PM   #16
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I wish it was an AP class, so I could take the test and get a chance for college credit. But the school does not offer AP physics, so this is an honors class. It's unlike any I've taken before, the teacher says he hopes to get into third semester stuff at the end of the year. I've never taken Physics at another school before, so I don't know how it compares.
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Old 02-16-07, 07:03 PM   #17
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Quote:
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I wish it was an AP class, so I could take the test and get a chance for college credit. But the school does not offer AP physics, so this is an honors class. It's unlike any I've taken before, the teacher says he hopes to get into third semester stuff at the end of the year. I've never taken Physics at another school before, so I don't know how it compares.
If your posting is any indicator, it's university level.
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Old 02-16-07, 07:44 PM   #18
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I don't think it's at all University level. We do nothing with AC in second semester's electronics unit. Also, we omit any and all air resistance calculations. Fluid mechanics, and some situations in circular and linear motion are not touched upon either.
Honestly, I was not prepared for this class at all. It's the only class I can't cruise through and do pretty well, with no effort on my part. Even now I don't do that well with grades. But, I think a portion of it is because of the teacher. I don't think he is the best teacher. Not so much that he is bad at teaching, he is very good at the verb of teaching. He obviously knows his stuff. But he gets steered off topic, we introduce a new topic 10 minutes before the end of class, not even having seen one complete problem, and are expected to know it for next day's quiz. He tells me I need to see him during free time for help, so I do, and he just ends up leaving. I don't think he fully explains a concept fully, and we are just expected to understand it. Still, it's by far my favorite class because of the subject so I stick with it unconditionally.
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Old 02-16-07, 08:06 PM   #19
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I don't think it's at all University level. We do nothing with AC in second semester's electronics unit. Also, we omit any and all air resistance calculations. Fluid mechanics, and some situations in circular and linear motion are not touched upon either.
It is university level.

I am a junior, and I just started fluid mechanics. I took physics 1 and 2, and AC circuits was physics 2. I'm in advanced dynamics now, and we're still learning things about rotational mechanics. It sounds to me like you're in a seriously advanced high school physics class.

No, it's not going to let you skip college, but you'll be in for a lot of review.
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Old 02-16-07, 08:20 PM   #20
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So I will actually look studious for my first year of college .
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Old 02-16-07, 09:53 PM   #21
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You should build a time machine so you can go back and never get involved with that nutty-ass ex-girlfriend of yours.
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Old 02-16-07, 10:01 PM   #22
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I was thinking I could make a van de graff generator so both of us can be negatively (or positively) charged. That way there is a strong repulsive force
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Old 02-17-07, 12:48 AM   #23
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I am an AP physics teacher, and the question your teacher asked was very appropriate for an AP physics course.

Find the net (vector addition) electric force (Coulomb's law) on the charge on the corner of the 'square' , find the acceleration of its mass (Newton's second law)... not terrifically difficult. Hate to say it, but you should have studied more.

The best form of study is to do many, many problems with some form of feedback (hopefully positive feedback... unlike this post).

Good luck, and get real.

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Old 02-17-07, 06:38 AM   #24
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Quote:
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I am an AP physics teacher, and the question your teacher asked was very appropriate for an AP physics course.

Find the net (vector addition) electric force (Coulomb's law) on teh charge on the corner of the 'square' , find the acceleration of its mass (Newton's second law)... not terrifically difficult. Hate to say it, but you should have studied more.

The best form of study is to do many, many problems with some form of feedback (hopefully positive feedback... unlike this post).

Good luck, and get real.
Hey, did I say I didn't get that problem? I actually did solve it. Or at least I had the right method, I think I did a calculation error. Either that I my lack of chemistry knowledge is worse than I thought
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Old 02-17-07, 12:59 PM   #25
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I've said it before, and I'll say it again - your instructor is Fruit Loops.
Sounds like all science to me. Why would he show you everything. Half of science is being able to figure **** out. I hated science because of it, but if thats the direction you are going, I would think you should get used to it.
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