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  2. (I have purposely avoided reading all of the contributions offered to date) A pendulum with no mass is not actually a 'pendulum'. Without mass, there is no gravitational force acting on the 'bob' or the 'rod'. In fact. that zero-mass bob on the end of the zero-mass rod is not going to respond to F = ma because, in this case, m = 0. Someone else can take it from there.
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  4. I'll simplify my suggestion: 1. The ball wants to fall vertically in Y axis due to the force of gravity. 2. The cart can only push/pull in X axis (i.e. it can not push ball upward in Y direction). This limits all forces to right the pendulum in the X axis.... so the force of the falling ball has to be translated to X axis. 3. The ball-on-a-stick is a classic torque model where the rotational force at the fulcrum can be broken into an X and a Y component proportional to the angle. (Typically θ is drawn between the arm and X axis and cos θ would be used to obtain X component of force but in this case sin θ is needed) Once the relationship with the torque's X component is expressed, the rest is just translating this to the pulley and strings then translating to voltage.
  5. afgan

    afgan

  6. oh forgot to mention I did NOT use the same dist cap and wires as the prior running video (ones from my car). So will also put that back on to be sure I don't have spark issue.
  7. I was doing that some during the video, it will misfire badly then as I advance the throttle, suddenly all will all fire and smooth out. I finally got a halfway decent idle after doing that for a while. This was with the cold water keeping the engine at about 70f, and the best run was with the temp switch disconnected (it was about 1.6k IIRC at pin 13 when connected with the cold water). I was hoping with the rad and the controlled temp it would idle better, but I struggled to get it to idle at all today. Again it would sputter and then catch on and run well (with lots of throttle), but never got settled down with any kind of reliable idle. This was all before I realized I had the idle screw completely closed off. I just could not find the sweet spot today. I did find the AAR was completely blocked off, will not open even after sitting for hours. I replaced it with the good one and will try again tomorrow. Will give it another go tomorrow and this time will resist the urge to mess with the AFM while its running. The plugs were caked with soft cabon deposits, brand new plugs in just a few minutes of attempting to run. The water temp sensor was down into the low 100's this time with the 180f t stat (tested at pin 13 and ground). I confirmed no leaks at the CSV. will double check the FPR vacuum line, but it was ok on the bench. Pressures all seem normal.
  8. Hi Kats, It looks like the numbers shown in the table are correct. Not sure why the numbering was different on the early RH seats. One of my parts books came from Nissan USA's HQ and has hand written notes when the part numbers changed or when parts were NLA. Also included a picture of the page with the vinyl swatches that includes the blue vinyl.
  9. Located in Hunting Park, CA. Includes HLS30-1625 with its original matching numbers engine. You guys in SoCal live in a Z-car hotbed! Here's the CL listing: https://losangeles.craigslist.org/lac/pts/d/huntington-park-3-datsun-240z-2-series-1/6873123172.html
  10. Have you given it some wide open time? Get the fuel flowing through those old crusty injectors, with the pintles banging open and shut. Probably help clean up the plugs too.
  11. True. A lathe might be the way to do it. Set it up so that one journal is centered and the other should be too. Maybe a flat surface with the axle journals on it and a bright light under the contact points, or some very fine feeler gauges. But the dilemma here is the axles could be fine, but the seating of the inner race is not. Just looking for confirmation. Since he has new bearings coming, he might as well pull the ones he has and reseat them. Maybe swap bearings on the axles in question and see if the problem follows the axle or the bearing, or neither. Maybe one of the bearings has a bent ball retainer, for example. Once the two races get aligned the retainer locks up? Or the inner race itself is defective. Could be cracked. Just guessing. A bearing swap might tell something.
  12. Woof. I feel for ya. Do the math. Get the grades. Collect the paycheck. In theory, it'll be worth it in the end.
  13. If the control loop is working properly, then theta should be very small. Problem is to make the control loop work properly. Actually for the second section, if you are allowed to use the feedback pot on the pendulum shaft, "theta" becomes a "concept". You just need volts: "The pendulum angle is measured with a single-turn potentiometer, with ±10V output corresponding to ±160˚ of rotation" That means you've got +10 V when the pendulum is almost horizontal in one direction and -10V when it's almost horizontal in the other. You've got 16 degrees per volt or (the inverse of that) 62.5 mV per degree. You're striving to keep the pendulum pot output at 0.00000 volts. And every 62.5 millivolts you are away from that is one degree off vertical.
  14. Cool. It's money, but those bearings aren't the kind of thing you want to do any more times than necessary. Glad to help and good luck with the rest of it. Keep us posted as to how it all turns out. I'm having a hard time picturing a good way to measure things to look for problems (like a bend) with a stub axle. You need good reference points and I'm not sure what you would use and how you would fixture it. The only precision surfaces on the axle are the bearing journals, but how would you detect a minute bend in the shaft between the two? What you're really looking for is that the two bearing journal circles are not on the same axis center anymore. How would you fixture to detect that?
  15. Hey guys, this is Georgia (the daughter working on the project, and yes @motorman7 it's a college problem 😂.) A true engineer at heart! It's the thought that counts right? When writing the equations to account for the angle, would it be fair to assume that theta is very small so as to simplify the sine and cosine aspects of the equation? I believe it is, but I am also ending up with a fourth order equation which is only slightly the worst thing ever to solve. 😁 -G
  16. Wow... That's no fun. At all. Due in two days, huh? I'm assuming this is a final project for a control theory class? I can't give you any hard answers, but might be able to help a little bit in some areas. First thing to do would be to define the project... It appears to me that there are two major approaches that should be applied to solve the problem: a) First approach (the "classical control method") in which the single output of the system should be the cart position (NOT the pendulum angular position). So the only thing you have is the force required to move the cart. If the pendulum is not vertical, the force required to move the cart in the direction of the (off center) pendulum will be greater than if the pendulum were perfectly vertical (in equilibrium). And the force required to move the cart AWAY from the (off center) pendulum will be LESS than equilibrium. So it sounds to me that the "classical control method" would be to rock the position of the cart back and forth (sinusoidal) and measure the force required to move it. That force should be able to be derived by the current necessary to rotate the motor. That's where the PD lead-compensator stuff comes in... You should be able to keep the sine wave constant and as small as possible. And there is some doubt about the success of this approach as laid out in the original problem. You are supposed to program it all up this way and see if you can make it work. And if not, explain why not. For example, the control loop may not be stable and you may find that the sine wave required is increasing in amplitude until you run out of track length. I suspect this approach is not very robust and resistant to outside applied interference (the bump nudge described in the problem). b) The second approach allows the student to utilize the position feedback on the pendulum and it becomes a more direct control loop. Move the cart in the direction the feedback pot tells you to and strive to keep the output of the feedback pot at 0V. That should be much faster and more accurate feedback than using the cart force and should be able to do a much better job of compensating for externally applied interference. (Proof is left to the student.) If I understood the project correctly, then I would break it down into pieces: Write some equations for the force required to move the cart independent of the pendulum. Write some equations for the force on the cart due to the position of the pendulum (this is the part that Blue started working on above). Then combine the two. Write some equations for the relationship between the rotation of the shaft and the linear position on the cart. Write some equations for the electrical energy required to rotate the shaft. Etc... I'm so glad I graduated!!
  17. wish I could make it this year but can't make it happen
  18. https://www.vtowheels.com/Lemans-15-x-7-4-x1143mm-18mm_p_126.html
  19. An inverted pendulum is a metronome (sp), if that helps. 😀 Bonzi Lon
  20. Just remember that the period of oscillation is independent of the mass of the pendulum. Ha ha ha... Wikipedia. I don't know any of this. And don't feel bad, Galileo had problems too. Maybe you should pray. https://en.wikipedia.org/wiki/Equations_of_motion "Galileo did not fully grasp the third law of motion, the law of the equality of action and reaction, though he corrected some errors of Aristotle. With Stevin and others Galileo also wrote on statics. He formulated the principle of the parallelogram of forces, but he did not fully recognize its scope. Galileo also was interested by the laws of the pendulum, his first observations of which were as a young man. In 1583, while he was praying in the cathedral at Pisa, his attention was arrested by the motion of the great lamp lighted and left swinging, referencing his own pulse for time keeping. To him the period appeared the same, even after the motion had greatly diminished, discovering the isochronism of the pendulum. More careful experiments carried out by him later, and described in his Discourses, revealed the period of oscillation varies with the square root of length but is independent of the mass the pendulum."
  21. I love this video, especially the first minute ....😀😀😀
  22. I just picked up a set. I'll post pics when they are installed on my '71 Z. Mike
  23. DRTY_S30

    DRTY_S30

  24. Took a few minutes to customize the @silverminemotors rear disc brake and park brake adapters. The supplied raw aluminum finish looked good, but I thought it would look better on my car with a nice gloss black finish. First a nice sandblasted texture, still drying from the cleaner...: And some gloss powder: And again after 30 minutes at 425 degrees! Now to just chase the threads and we should be good to go!
  25. While I wait for more brake components to get finished, I thought I would test out this new Park Brake cable from @silverminemotors. Available here from Edan: Park Brake Cable This original equipment was worn out and not suitable for the new Wilwood park brakes. The new cable is complete with the cir-clips needed to secure it to our setups, and fits nicely through our rubber hangers. I will get some more pics of the setup as I connect them to the park brakes. And one without the glare of the flash under the car... The length of the cable looks perfect so it should allow some flexibility in the custom setups for different people. I like it!
  26. Ahh okay. I understand now. I plan to do the upgrade to an '85 maxima alternator since it is direct bolt on and puts out 80-90A. How do people usually handle the fuel pump wiring when doing the alternator upgrade? Is wiring it through a switched source with inertia switch common to do for the Z's? You are correct that the seat belt interlock has been bypassed so it is a non-issue. I just purchased my 260z and am still learning how a car works. I am doing a lot of studying up on the car so I can begin to "modernize" it. I have never been a DIY car guy but I'm excited to start. I am fairly confident in my electrical skills so I am more comfortable starting with upgrading the electrical system first 😄
  27. I think it is just a torque problem. The basic element is force in the +X direction from the car on the ball transmitted along the shaft has to counter the -X direction force of mg from the ball falling.... which I believe is proportionate to sin θ. When θ is negative and the ball falls in -x everything is reversed. Equation of motion is F=ma for the cart where F is equal to the X component of F=mg Sin θ from the falling ball. Seems like a Segway. btw I'm not an engineer 😉
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