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#31
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Re: 2015 Beta Testing - The Components are Here.
I have a question regarding the discrete wire terminals used for low current power distribution and the CAN bus. I'm not familiar with that style of terminal. Can someone post a link to the manufacturer or some document describing how they are used?
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#32
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Re: 2015 Beta Testing - The Components are Here.
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#33
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Re: 2015 Beta Testing - The Components are Here.
You'll find a good description of the connectors here:
http://www.fightingpi.org/Resources/...20Module.shtml manufacturer: http://catalog.weidmueller.com/catal...15980277147218 With the right wire you don't need to push the button to insert it, but we've found most stranded wires require us to push the button. You also need to strip the correct amount of insulation, but really that's not any different than other connection styles. Last edited by Tom Line : 18-08-2014 at 22:12. |
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#34
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Re: 2015 Beta Testing - The Components are Here.
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#35
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Re: 2015 Beta Testing - The Components are Here.
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#36
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Re: 2015 Beta Testing - The Components are Here.
My big question is whether or not we will lose encoder counts while that happens (encoder brownout). The digital side car would brown the encoders out below 5.5 volts, which caused us to destroy a gear once. We'll have to add that to our list of things to test.
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#37
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Re: 2015 Beta Testing - The Components are Here.
I had an opportunity to take mount hole measurements of the 3 new CRE parts.
If you would like my super rough CAD (boxes with holes), message or email me. Can't be off than more than a hundredth or two here or there. Sorry ahead if I don't respond immediately. Will be out of town till the weekend. ![]() |
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#38
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Re: 2015 Beta Testing - The Components are Here.
Could you post the quick measurements? I expect that at this stage most people are mainly interested in seeing whether the centre-to-centre distances are multiples, 1/4", 1/2" 10mm, 20mm, etc.
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#39
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Re: 2015 Beta Testing - The Components are Here.
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Code:
VbattIn ----[6 V "servo" supply]-----[current limit/disable]---6 V terminals
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----[5 V user supply]-----5 V terminals
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--[3.3 V user supply]---3.3 V terminals
It does mean there is now ~ 0.6 V between when the motors are disabled and when the 5 V and 3.3 V supplies shut down instead of them happening at the same time. I'm also working on a feature that will allow the FPGA to stop motor controllers (probable source of brown-out in non-pathological case) in far less time. The plan is to actively send one PWM pulse of "idle" when commanded to disable by the watchdog / power monitor before stopping the generation of PWM signals. Because the motor controllers are not continuing to draw high current for as long, the voltage drop should be less severe. This should reduce the time from brown-out detection to load removal from 100 ms +/- 5ms to about 10 ms +/- 5 ms. |
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#40
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Re: 2015 Beta Testing - The Components are Here.
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#41
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Re: 2015 Beta Testing - The Components are Here.
I would imagine that the Voltage Regulator Module (VRM) would be more tolerant to voltage drops. It provides both 5V and 12V regulated output, but I don't know what the specs are for brownout conditions on it.
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#42
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Re: 2015 Beta Testing - The Components are Here.
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#43
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Re: 2015 Beta Testing - The Components are Here.
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This ends up being a rules and robotRIO internals question. Designing a board (and/or using the CTRE regulator) to supply encoder power is far easier than designing an entire co-processor setup, which 971 has been doing for years. I've debugged enough problems on bots over the last couple years which ended up being encoder brownouts that I take this pretty seriously. |
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#44
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Re: 2015 Beta Testing - The Components are Here.
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You are driving the robot, while moving an arm. You change directions quickly on the drive base and pull a ton of current to the motors. The +5V rail browns out for about 100ms, but the arm is still moving, so you "skip" maybe 5-10 degrees worth of rotation on a quick arm. Next time you command the arm to a position near the limit, it slams in to it without remorse. We have built custom electronics to overcome this in the past, but perhaps it would make sense to make something more generic. Maybe a board that sits of the expansion port and takes power from the VRM? All high priority inputs would route through this. Last edited by Tom Bottiglieri : 19-08-2014 at 16:39. |
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#45
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Re: 2015 Beta Testing - The Components are Here.
What about adding in limit switches to your mechanism to detect max travel distance and calibrate the encoder on the fly?
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