View Full Version : 3-way PWM Splitter
J-Chillin
23-01-2016, 15:00
Hey so our team has found a way to run 3 motors on our drive train to one PWM signal. Does anyone know where we can find a 3-way PWM splitter? All the ones we've been finding are 3-way but don't have the right connectors. Thanks!
You could always use two two-way splitters. Attach one to one leg of the other, bundle the excess, and you have a three-way splitter.
Greg Needel
23-01-2016, 16:08
Hey so our team has found a way to run 3 motors on our drive train to one PWM signal. Does anyone know where we can find a 3-way PWM splitter? All the ones we've been finding are 3-way but don't have the right connectors. Thanks!
I would make your own by soldering multiple cables together.
We (REV) provided a bag with 8 PWM cables, 2 Y cables, and a 2 wire jumper this year. If you cut the heat shrink tubing off of the Y cables it should be easy to solder in an extra lead from one of the PWM cables cut down. Remember that you don't need to solder the red wire at all as it is not connected to anything in your motor controller anyway.
All that being said, are you using so many motors that your roboRIO has no free ports? As an alternative, you could wire each motor controller individually to the RIO (and if you run out of ports you could use the extra ones broken out from the MXP connector.
Hey so our team has found a way to run 3 motors on our drive train to one PWM signal. Does anyone know where we can find a 3-way PWM splitter? All the ones we've been finding are 3-way but don't have the right connectors. Thanks!
In case someone wants to try this with the older motor controllers: does anyone know if a single roboRIO PWM output can reliably source enough current to drive 3 of the older low-input-impedance controllers ?
Avoid mixing makes AND models of motor controllers. Most of the ones I have looked at use a photocoupler as the input device. The different models, even if they came from the same manufacturer are likely to use different photocouplers. Different photocouplers will likely have different Forward Voltages, VF. If you put different controllers, with different VF's, only the one with the lowest VF will work.
nandeeka
23-01-2016, 23:08
Is this even legal given R53?
R53 Each power regulating device may control electrical loads per Table 4-4. Unless otherwise noted, each power regulating device shall control one and only one electrical load.
rich2202
23-01-2016, 23:21
R53 applies to the Motor Controller, not the PWM signal that controls the Motor Controller.
If you are running out of PWM ports, you might want to consider CANbus to control the motor controllers.
Al Skierkiewicz
25-01-2016, 08:02
philso,
None of the controllers that I have looked at have a raw opto-coupler input connected to the PWM port. There should be a series current limiting resistor so the V forward difference should not show up as a problem. That being said, single point of failure is likely to raise it's ugly head if one is not careful. A bad controller will take down all three, a pinched wire will take down all three. Your mileage will vary.
marshall
25-01-2016, 08:36
I would make your own by soldering multiple cables together.
We (REV) provided a bag with 8 PWM cables, 2 Y cables, and a 2 wire jumper this year. If you cut the heat shrink tubing off of the Y cables it should be easy to solder in an extra lead from one of the PWM cables cut down. Remember that you don't need to solder the red wire at all as it is not connected to anything in your motor controller anyway.
All that being said, are you using so many motors that your roboRIO has no free ports? As an alternative, you could wire each motor controller individually to the RIO (and if you run out of ports you could use the extra ones broken out from the MXP connector.
I want more of your 2-wire jumpers!!!! They are very nice quality.
You please to make nice special price for me on world wide web? (I looked and could not find them on the REV site, are they available to purchase?)
philso,
None of the controllers that I have looked at have a raw opto-coupler input connected to the PWM port. There should be a series current limiting resistor so the V forward difference should not show up as a problem. That being said, single point of failure is likely to raise it's ugly head if one is not careful. A bad controller will take down all three, a pinched wire will take down all three. Your mileage will vary.
We confirmed with the manufacturer that we should not have been paralleling the inputs of the two types of motor controllers we had and that the LED VF's were the problem. Once we had only controllers of one type connected together, they all worked properly. We had no defective motor controllers.
Perhaps some of the motor controllers have a current limiting resistor in series with the LED. If the one with the lowest VF does not have a current limiting resistor, it will still prevent the other ones from turning on.
Greg Needel
25-01-2016, 09:56
We confirmed with the manufacturer that we should not have been paralleling the inputs of the two types of motor controllers we had and that the LED VF's were the problem. Once we had only controllers of one type connected together, they all worked properly. We had no defective motor controllers.
Perhaps some of the motor controllers have a current limiting resistor in series with the LED. If the one with the lowest VF does not have a current limiting resistor, it will still prevent the other ones from turning on.
The SPARK has a 150 ohm series resistor with the optocoupler's LED. If you are curious about anything else inside the spark our complete schematic is in the back of our users guide on our website. http://www.revrobotics.com/wp-content/uploads/2016/01/REV-11-1200-UM-00.pdf
Greg Needel
25-01-2016, 10:17
I want more of your 2-wire jumpers!!!! They are very nice quality.
You please to make nice special price for me on world wide web? (I looked and could not find them on the REV site, are they available to purchase?)
We decided not to sell these (or any of our cables) this year as we couldn't offer a significant savings over what teams already are buying or are available other places online.
Send me a PM, I might have some lying around I could send you if you let me know what you need.
Carter1671
25-01-2016, 16:08
In case someone wants to try this with the older motor controllers: does anyone know if a single roboRIO PWM output can reliably source enough current to drive 3 of the older low-input-impedance controllers ?
Hey! PWM does not supply the power to the motors, just tells the motor controllers when and how to run the motors. So, a single PWM output from a roboRio to three motor controllers should be okay.
Hey! PWM does not supply the power to the motors, just tells the motor controllers when and how to run the motors. So, a single PWM output from a roboRio to three motor controllers should be okay.
Hi Carter. Welcome to Chief Delphi.
Check out this thread. It will give you the necessary background for the question:
http://www.chiefdelphi.com/forums/showpost.php?p=912501&postcount=5
Andrew Schreiber
25-01-2016, 17:06
In case someone wants to try this with the older motor controllers: does anyone know if a single roboRIO PWM output can reliably source enough current to drive 3 of the older low-input-impedance controllers ?
I don't know about the RoboRIO, but my AR400 RX is capable of driving 4x of the old style Talons while being powered off the 5V rail on a PDB and it's not exactly a high end piece of kit (I think it was the cheapest 4 channel RX my local store had) [1] Unless you mean old 884/883 style Victors in which case, I'd have to wire something up.
[1] mechanical folks wanted all motors tied to one stick. I could either put a full control system on the bot or cheat and use the RX/TX system I had sitting around for other things. I'm lazy.
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