Robot Inspection and Build Rules - Electrical - Answer Thread

[Wil Wheaton]

Hello. Our team was wondering if we could use this chip since the ZTE phone doesn't have a built-in gyro sensor. Thanks for clarifying!

http://www.adafruit.com/products/2472

Team 8548

A: In general, it is not possible for the GDC to rule on the legality of all possible manufactured sensors. This sensor is an example of a broad class of sensors that are legal within the limits imposed by <RE06> and other rules.

All questions about similar sensors will be mitigated to the "duplicate questions" forum.

[Wil Wheaton]

With support for Legacy Matrix motor controllers not yet available, our team has adapted a working robot with the following configuration:

New Modern Robotics Core Power Module
New Modern Robotics Motor Controllers
Legacy Matrix 9.6v Motors
Legacy Matrix 9.6v Battery
Standard ZTE Speed Phones for Driver Station and Robot
Standard Driver Station & Robot Apps, with custom op mode

Note: This configuration does not provide motor encoder use/feedback, we are using power leads only on motors.

As per current rules RE01 (control modules), RE03 (power) and RE04 (motors & servos), the described configuration would only be legal for competition if we were using Legacy Matrix Motor/Servo controllers.

As support for the Legacy Matrix Motor/Servo controllers is not yet available, no firm release date has been announced, and as we have no other options available, we are requesting that the applicable rules be adjusted to allow our team (and potentially others) to use the described configuration for the 2015/2016 season.

Thank you for your time and consideration,

Redfish Robotics
Team 9958
"We're Hooked on FIRST"

A: No. This alternate configuration is not allowed. Matrix Controllers are now supported in the SDK.

[Wil Wheaton]

<RG04> says that "Any compatible servo is allowed"; Q&A Forum update #9 says "Make sure to pay attention to the stall current ratings."

Does this mean that the TETRIX Quarter Scale Servos (#W39904 and #W39905) are no longer legal if used with the ? Both of these servos list a stall current rating of 1800mA; the MR Core Servo Module says individual servo power is 6 volts DC 1.5 amps max.

Thanks!

FTC7172

A: Both the Legacy HiTechnic Servo Controller and the Modern Robotics Servo Controller have the same 5 amp total current limit. The total stall current rating for servos attached to a servo controller must stay below this 5 amp limit.

[Wil Wheaton]

It is not clear to me why the sensor referenced in Post #18 is not allowed while the sensor in Post #21 is allowed. Both appear to be sensors that offer on device processing. Perhaps the distinction is that the sensor in Post #19 has a micro controller which appears allow full customization? As opposed to Post #18 where the micro controller and firmware is is provided by the vendor (Bosch). I am just looking for a way to distinguish between the two types of sensors so we can apply this to other sensors we might select.

Post #19 - https://www.sparkfun.com/products/10736
Post #21 - http://www.adafruit.com/products/2472

5385

A: The Sparkfun sensor includes a on-board processor that is user programmable and is effectively an Arduino board with sensors included. The Adafruit sensor is not user programmable, only configurable.

[Wil Wheaton]

(This question was previously addressed for the legacy Motor Controllers:
http://ftcforum.usfirst.org/showthre...-Answer-Thread #3)

With the shift to the new hardware, is it acceptable to wire 2 motors to a single channel of Modern Robotics Motor Controller?

A: Yes. It is acceptable to wire up to 2 motors in parallel to be driven by a single motor controller. Care should be taken during the electrical design process to avoid overloading the motor controller. The internal thermal breaker takes significant time to cool and reset once tripped.

[Wil Wheaton]

Is it possible to use an optical encoder on Tetrix motors which is different from the one sold by Tetrix, (I believe this one is produced by US Digital), assuming that the alternate has input power and output quadrature which are the same as the Tetrix encoder (5V TTL compatible)? The encoders sold by Tetrix are expensive, and we have found them in the past to be quite fragile and somewhat lacking in reliability. It seems there are several other encoders out there that would be less expensive, more rugged, and compatible with the motor controllers.

A: Encoders compatible with the Modern Robotics Motor Controllers and Legacy HiTechnic are allowed. Care should be taken to match the specifications of the Tetrix encoders exactly as the PID code that runs within the motor controllers relies on the characteristics of the encoder. Encoders not compatible with the Motor Controllers may be used as connected to a Core Device Interface.

[Wil Wheaton]

My team has two tetrix motor encoders from previous years, it appears they will not work with the new system. Is this accurate?
http://www.tetrixrobotics.com/TETRIX...Pack?SKU=38000

FTC 7503

A: There is nothing in the rules that would prohibit the use of the above encoders. They are compatible with both the HiTechnic motor controllers and the Modern Robotics Controllers.

[Wil Wheaton]

In previous seasons, teams had electrical troubles when their power was daisy-chained through the HiTechnic motor and servo controllers. This is because when a lot of current was drawn by a motor (e.g., if it was stalled, or changing direction, etc.), the large current passing through the small trace on the printed circuit board inside the controllers resulted in a downstream voltage drop which could affect the electronics. The FTC Robot Wiring Guide, released by FIRST, specifically identified this as a problem and proposed the solution of using external power distribution terminal/splitter/network which bypasses power being distributed through the controller's printed circuit board traces. See for example, page 18. of the FTC Robot Wiring Guide. http://www.usfirst.org/sites/default...ring_Guide.pdf

This year, the game manual states that we must route all power through the new Power Distribution Module. This essentially requires that ALL power now go through traces on the Module's printed circuit board, which again can result in the same problem identified in the FTC Robot Wiring Guide.

So, our question is, may we use an external power distribution terminal/splitter/network as suggested in the FTC Robot Wiring Guide instead of or in addition to the power distribution option in the Power Distribution Module? Please consider that a lot of time and trouble was spent by FIRST in making the FTC Robot Wiring Guide to address previous chronic power distribution problems, and we humbly suggest that the recommendations in that document be at least permitted as an option for teams concerned about the same issues.

A: Power splitters are explicitly allowed per rule <RE05>.f. They may only be used downstream from the Core Power Distribution module ... i.e. the battery must connect to the Power Distribution module with nothing more than a (recommended) single power switch between.

[Wil Wheaton]

We're concerned about possibly burning out motors or motor controllers, so we want to insert a 1 ohm resistor in series with the motor controller 12 volt input to limit the current. Is this allowed or is it a violation of RE06 or another rule? We noticed passive components are allowed for creating voltage dividers for sensors. Thank you for your help.

A: No. Resistors are not allowed to be placed inline with DC motors per <RE06>.d

[Wil Wheaton]

Hello I have a question about preventing our robot from being affected. Can we have our robot store static electricity in a battery as long as we don't use it for our power source? Thank you!

A: No. Per <RG10> and <RE03>.