EricVanWyk
05-01-2014, 17:27
Hey all! I wanted to let you know that the Mooshimeter (the wireless datalogging multimeter I've been working on with James) is going up for pre-sale tomorrow. I wanted to give ChiefDelphi a head's up because there will be a limited number of "early-bird" meters available for super cheap, and I'd love for FRCers to get that discount.
The super quick TL;DR; is to head over to check out the video (http://youtu.be/TIJ8R2O1WJc) first and then look at the features at our website (http://moosh.im/mooshimeter/). We'll alert our mailing list first, so be sure to register to snag the discount.
The longer version is that we've created a new type of multimeter that addresses a few issues that I've encountered during my tenure in FRC (student in 2000, mentor in 2004, control electronics developer since 2006, (lead) robot inspector since 2011/2012). Hopefully this will save y'all a few of the pain of some of my learning experiences that featured thermally assisted rapid disassembly events or chasing after bots with long tether cables.
Here are some relevant portions of this year's robot rules:
R42: With the exception of one (1) cRIO and one (1) Solenoid Breakout Board, no other electrical load may be connected to the 24 VDC supply terminals on the PD Board.
R69: If powered from the PD Board 24V supply per R41, loads on each Solenoid Breakout shall not cumulatively exceed 16W if using the cRIO-FRC (8-slot) and 21W if using the cRIO-FRC II (4-slot).
Pulling too much from the 24V rail can affect the supply's ability to handle low voltages and transients, and could potentially reboot the cRIO. I designed that converter with a good bit of margin, but those limitations are there for a reason. This can be quickly checked by the Mooshimeter by simultaneously measuring current and voltage in this branch circuit.
R37: All wiring and electrical devices, including all Control System COMPONENTS, shall be electrically isolated from the ROBOT frame. The ROBOT frame must not be used to carry electrical current.
This is a tough one to verify during inspection. Inspectors are told to measure resistance between the electrical system and the frame, but this only catches the shorts that are active when the robot is powered off and not moving. I've inspected plenty of robots that are sensitive to vibration or only have a short when it is in a particular position. Also, it is hard to catch motor casing shorts like we had a while back without checking every single motor and rotating the shaft. When the robots are off, motor controllers are high impedance.
A Mooshimeter can check frame isolation on a moving robot, and save you the aforementioned potential unplanned thermal disassembly of your wiring (like the one that cost us an eliminations match a few seasons ago...)
R53: CUSTOM CIRCUITS shall not directly alter the power pathways between the ROBOT battery, PD Board, motor controllers, relays, motors, or other elements of the ROBOT control system (items explicitly mentioned in R64). Custom high impedance voltage monitoring or low impedance current monitoring circuitry connected to the ROBOT’S electrical system is acceptable, if the effect on the ROBOT outputs is inconsequential.
The Mooshimeter's current and voltage monitoring modes fall into this category. The external current monitoring doesn't add any impedance, which should qualify it as "low impedance". The voltage monitoring is about 50x higher impedance than the PD's own blown breaker checking.
This makes it easy to monitor health and power use of the whole robot or individual branch circuits. Check out the current transients when you slam from full forward to full reverse!
The super quick TL;DR; is to head over to check out the video (http://youtu.be/TIJ8R2O1WJc) first and then look at the features at our website (http://moosh.im/mooshimeter/). We'll alert our mailing list first, so be sure to register to snag the discount.
The longer version is that we've created a new type of multimeter that addresses a few issues that I've encountered during my tenure in FRC (student in 2000, mentor in 2004, control electronics developer since 2006, (lead) robot inspector since 2011/2012). Hopefully this will save y'all a few of the pain of some of my learning experiences that featured thermally assisted rapid disassembly events or chasing after bots with long tether cables.
Here are some relevant portions of this year's robot rules:
R42: With the exception of one (1) cRIO and one (1) Solenoid Breakout Board, no other electrical load may be connected to the 24 VDC supply terminals on the PD Board.
R69: If powered from the PD Board 24V supply per R41, loads on each Solenoid Breakout shall not cumulatively exceed 16W if using the cRIO-FRC (8-slot) and 21W if using the cRIO-FRC II (4-slot).
Pulling too much from the 24V rail can affect the supply's ability to handle low voltages and transients, and could potentially reboot the cRIO. I designed that converter with a good bit of margin, but those limitations are there for a reason. This can be quickly checked by the Mooshimeter by simultaneously measuring current and voltage in this branch circuit.
R37: All wiring and electrical devices, including all Control System COMPONENTS, shall be electrically isolated from the ROBOT frame. The ROBOT frame must not be used to carry electrical current.
This is a tough one to verify during inspection. Inspectors are told to measure resistance between the electrical system and the frame, but this only catches the shorts that are active when the robot is powered off and not moving. I've inspected plenty of robots that are sensitive to vibration or only have a short when it is in a particular position. Also, it is hard to catch motor casing shorts like we had a while back without checking every single motor and rotating the shaft. When the robots are off, motor controllers are high impedance.
A Mooshimeter can check frame isolation on a moving robot, and save you the aforementioned potential unplanned thermal disassembly of your wiring (like the one that cost us an eliminations match a few seasons ago...)
R53: CUSTOM CIRCUITS shall not directly alter the power pathways between the ROBOT battery, PD Board, motor controllers, relays, motors, or other elements of the ROBOT control system (items explicitly mentioned in R64). Custom high impedance voltage monitoring or low impedance current monitoring circuitry connected to the ROBOT’S electrical system is acceptable, if the effect on the ROBOT outputs is inconsequential.
The Mooshimeter's current and voltage monitoring modes fall into this category. The external current monitoring doesn't add any impedance, which should qualify it as "low impedance". The voltage monitoring is about 50x higher impedance than the PD's own blown breaker checking.
This makes it easy to monitor health and power use of the whole robot or individual branch circuits. Check out the current transients when you slam from full forward to full reverse!