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#16
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Re: Low Cost Encoders
Giving fair warning to set expectations accordingly.
Several things have cropped up for this weekend that will delay my testing. I am working on it but in addition to the other obligations I ordered something which may not arrive on Saturday as I expected. I will post what I can as soon as I can. |
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#17
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Re: Low Cost Encoders
Yes, I do believe that there are companies who steal intellectual properties. My post was related to intellectual properties and not where it is made. It doesn’t matter who steals from whom, whether its US based company who steals from non US company or the other way around. The company that designs products invests lot into their design and testing. More over these companies spend lot in making sure that their product stands by their specifications and meets industry standards. I was a Design and Application engineer and I know what goes into a product development.
It’s naïve to think that this does not happen. Recent dispute between Apple and Samsung is one example. And just don’t forget the lady who got electrocuted with fake iPhone charger! Before you vent your frustration, read the post and understand, my message did not mention anything about labor abuses. What “politics” are you talking about? My point is just plain and simple; before I put my money, I will do my best to make sure it does not go to thieves. It is not always easy or simple, but when someone is selling for half price, it raises a red flag! This is for those who steal! |
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#18
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Re: Low Cost Encoders
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I will dismantle these encoders, post pictures and then you can make your case. It is round, can like, has a 6mm shaft is not theft of anything unless you want to show me the design patent on that form. Surely quadrature encoding itself is not subject to any existing utility patent I am aware of. Prior art would be acceptable as evidence but for something as simple as the way that picture looks it really is pressing on the point of being a bit silly. Once again without that evidence and without any patience to get that evidence you assume these are stolen designs. It's just not acceptable to me. I too am an engineer. I have 2 patents pending. I too would be *quite* annoyed if someone anywhere just simply took my work. However I would not assume they did so. All technology tends to be derivative. You can't blame a tire manufacturer cause they didn't invent the wheel. You can't blame V-Tech because they didn't invent the telephone. I think it would be very ungracious professionalism if one FIRST team went at another for shooting frisbee because they did to. People do arrive at similar solutions from different places all the time. It is not magic that so many teams use wheels to shoot frisbee. Should I be annoyed at that? As far as Apple and Samsung is concerned that is an example of business usurping engineering and a patent system that is utterly broken. We've got patent trolls sitting on mountains of valid ideas that are trapped because they have *no intention* to use those ideas as anything but weapons against innovation. So even mentioning that is political. Apple did not invent the GUI and neither did Xerox. That idea was military technology long before they used it. Yet for a *very* long time Apple ran around accusing Microsoft of stealing their idea. Really? STEM means scientific method should have a very firm grip on this community. If your concern is that this is stolen: wait for me to do the work for you to prove the point. If your concern is that this is unreliable: wait for me to do the work to demonstrate that. Doing this as you are is political plain and simple. You are not following scientific method. You are trying to 'poison the well' with suspicion and allegation. That sort of business is natural for humans but science has to be above it. Last edited by techhelpbb : 18-08-2013 at 11:18. |
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#19
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Re: Low Cost Encoders
Finally all the parts arrived:
So I have a 5V 4096 position per revolution stepper (it is geared down) with ULN2003 to be driven by an Arduino or the like. A dual LS7366R quadrature encoder PCB to monitor the encoder outputs. U.S. Digital sells this component I bought the PCB from SuperDroidRobots.com. A ServoCity set screw hub for the stepper. A ServoCity set screw hub for the encoder. They are different size bores. The same 6-32 tapped bolt pattern. The Chinese encoders to be tested. Now I need to make a mount and wire this up. Then I will have set up a realistic environment turning the encoder back and forth for an extended period of time. I will be able to tell if the encoder is missing pulses because I will mount 2 limits at either end of the rotation (so it won't rotate all the way around). I will program the stepper to rotate till the encoder hits a point just before the limits on either extreme. If it misses (by any serious margin) it will smack the limit and an error can be recorded. Leave that run for a good long time and eventually it'll exceed the entire service lifetime FIRST will likely ever ask of it. Plus, of course, it gives me lots of time to record samples of the output waveform. As the entire motion is under Arduino control various speeds of rotation can be tested. It would be extremely unlikely the LS7366R would roll over or miss a pulse so it would be safe to say any error like that is the encoder or an electronic issue. Last edited by techhelpbb : 21-08-2013 at 22:49. |
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#20
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Re: Low Cost Encoders
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But I think your test is much better. |
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#21
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Re: Low Cost Encoders
Can you also report back on how much signal jitter there is or isn't when it's stationary. Sure a capacitor could easily address that, just want to know how stable the signal is.
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#22
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Re: Low Cost Encoders
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So hopefully you'll be able to get that from there. Just to manage expectations I wouldn't expect this done this weekend. With NASDAQ doing a dance yesterday I am a bit preoccupied. However I will work on it this weekend even if I don't finish it. Last edited by techhelpbb : 23-08-2013 at 13:36. |
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#23
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Re: Low Cost Encoders
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The oscilloscope signal sampling will be fine. Thanks for taking the time and effort to do this analysis. |
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#24
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Re: Low Cost Encoders
Could I have a propeller chip monitoring all the encoders and send all the data to the cRIO, using only 1 i2C digital I/O, or would that be illegal to the FRC rules?
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#25
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Re: Low Cost Encoders
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***** Disclaimer ***** It's not a design approach I would use or recommend. You have 2 single points of failure. The propeller chip, and I2C. A failure with either one, and you lose all of your encoder data. ***** /Disclaimer ***** |
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#26
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Re: Low Cost Encoders
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Since the Propeller is not interrupt driven there's a chance that at 2400 steps per rotation with a 20MIPS cog you might fall behind at high RPM. Unlike the ARM using an interrupt it won't generally freeze. It will just miss transitions. I actually do have a Propeller based PropASC+ here. For the sake of this test I decided against attempting this initially. I know these quadrature chips work so I'd rather not introduce user code where I don't need to. The code needed to do this in a Parallax Propeller is readily available. I am still working on this. Also building a CNC machine. Also writing code for another project so bear with me. So far no major issues. I'm a couple thousand into FIRST expenses so far this year so gotta keep all the things rolling. Last edited by techhelpbb : 08-09-2013 at 14:37. |
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#27
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Re: Low Cost Encoders
I don't want to rush you but I'll have a chance to make a order soon and I'm thinking of ordering a few. Any opinions so far?
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#28
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Re: Low Cost Encoders
So far they work fine.
I have been swamped by unplanned (not always bad) excursions. Hope I can commit more time this week. The biggest issue I see so far is the unusual for FIRST resolution. I will do my best to make sure to finish this month. That will leave you 8 weeks to order and ship. |
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#29
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Re: Low Cost Encoders
Quote:
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#30
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Re: Low Cost Encoders
It's the end of the month. Any news?
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