Transcript Document

Drive System Reliability
and Trouble shooting
April 29, 2006
Championship
Atlanta, GA
Jay TenBrink and Patrick Major
Goodrich H.S. Martians 494 and More Martians 70
DaimlerChrysler and General Motors
Agenda
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6.
Introduction (why we are here)
Drive system reliability
Trouble shooting
Corrective action implementation
Design for reliability
Questions and answers
Introduction
Jay TenBrink
Manager – FWDPT Chassis Engineering
Team 494 Engineering Coach since 2001
Patrick Major
Owner – Major Distributing Co.
Team 494 Head Coach since 2001
My Favorite Robot
Team 494 Head Robot since 2003
Why we are here

In 2003 team 494 developed the Robot Dynamometer
as a device for testing and developing robot drive
systems. This device applies a varying resistance load
to the drive wheels and measures the robot's speed.
Throughout 2003,4 and 2005 seasons, this dyno was
available for use to all teams at 3 regional events and
the Championship. Of the more than 100 robots that
have been tested approximately 20% exhibited a drive
system problem of some degree. In many cases, root
cause analysis took place on the dyno.

The Robot Dynamometer allowed this work to take
place on a static robot under any simulated speed or
load condition in a safe and controlled environment.
Since many drive system problems are not evident
when there is no load put on the system, conventional
root cause analysis can be difficult, imprecise, time
consuming, and even unsafe.
What we will share with you today:

Drive system reliability
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Examples of actual electrical and mechanical problems
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When, where, and why they occurred (we won’t say who)
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Trouble shooting techniques (root cause analysis)
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Safety precautions and root cause analysis do’s and don’ts
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Helpful analysis tools
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Corrective action implementation
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Appropriate repairs and avoiding collateral damage
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Verifying the fix
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Design and construction methods for reliability
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Basic DFMEA (Design Failure Mode Effects and Analysis)
What we won’t be covering here:
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Internal battery problems and how to avoid
and diagnose them
Internal motor problems and fundamental
drive system design flaws
However…
Many of the drive system fundamental
issues we address can be applied to other
robot systems (arms, claws, etc.)
Quote for the day
“It is good to learn from experience. It is better
to learn from someone else’s experience”
Author: unknown
Terms

Root cause - The heart of the issue, what started the whole
problem. Example: Did not crimp the wire terminal correctly.

Failure mode – The primary effect of the problem. Example:
Poorly crimped power supply wire increases the resistance of
the circuit, this decreases the voltage available to the entire
robot.

Secondary failure mode – Cascading failure brought on by the
primary failure mode. Example: When voltage drops, motor
power is decreased.

Symptom - A sign or indication of a problem that is neither a
root cause or a failure mode. Examples: Wires or terminals that
are hot to the touch, melted insulation, smoke, noises, odor, etc.

Corrective action – what you did to address the root cause.
Example: Fixed poorly crimped terminals.
Reliability Problems
What follows is a somewhat
comprehensive list of actual problems
that we have experienced first hand or
witnessed during our last four years
with the FIRST program.
Electrical Problems
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13.
Poor crimps on terminals (the grand daddy of them all)
Loose screws on terminals (battery, controller, etc.)
Mechanically damaged or cut wires
Shorting to the frame
Incorrect wire gauge or terminal size (too small)
Terminal size too large for the wire gauge
Loss of battery or battery cable becomes unplugged
Incorrect fuse size or non-functioning fuse
Damaged or discharged battery
Metal debris in electrical devices
Cracked or broken control cable connectors or device
Cold solder joint on electrical device terminal
Broken terminal pins on control wire connections
Mechanical Problems
1.
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4.
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6.
7.
8.
9.
10.
Drive train out of alignment and binding
Drive sprocket to wheel hub slipping under load
Wheel tread to drive wheel slipping under load –
especially on tank tread robots
Bevel gears out of place due to axial loads
Drill motor gear box in between gears
Drive chains coming off of sprockets during a match
Drive sprockets breaking (plastic sprockets)
Fractures due to removing too much material during
weight loss (AKA swiss cheesing)
Frame deflection under load from drive system
Set screws loosen and back out of sprockets
Common Drive System Problem
Symptoms
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7.
Electrical connections or wires are hot to the touch or
melt insulation on terminals or wires
Metal or plastic debris is present on the robot from
grinding, scraping, slipping gears, etc.
Robot lacks the power or speed it used to have
Robot only turns in one direction or will not move at all
Motors overheat and circuit breakers / fuses open
Main power supply circuit breaker opens
Sparks, smoke or foul smell is present
Trouble Shooting Do’s and Don’ts
(Root Cause Analysis)
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Do work safely:
Always wear safety glasses in the pit area or around live
robots, even if there is no action on your robot
Be aware of what your neighbors are doing (exercising or
testing their robot, grinding, testing, etc.)
Be aware of any stored energy device on your robot
(springs, cylinders, tank, battery, kinetic or potential
energy devices, etc.)
Be extra careful when powering up your robot in the pit
area. Never leave the controls of a live robot unattended.
Never make electrical repairs on a live robot. Electrical
shorts can cause severe burns and damage components
Keep loose objects out of the robot (sleeves, hair,
lanyards, body parts, etc.) Don’t lean over the machine,
walk around.
Trouble Shooting Do’s and Don’ts
continued
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Do select a leader for your root cause analysis activities
Do have a systematic plan of attack
Do discuss the plan with the students and mentors and get
feedback
Don’t rush, this almost always leads to careless mistakes
Don’t allow the evidence to be tampered with or destroyed before
the analysis has been completed. This is crucial!
Don’t wait to trouble shoot.
Some evidence has a short half life, so observe the symptoms
quickly and carefully (hot wires, open circuit breakers, smells,
etc.)
Do use all of your senses (except taste) to analyze the evidence
Visually inspect for anything out of the ordinary, foreign matter,
melted solder, broken plastic, etc.
Listen and feel for scraping, vibration, clunking, etc.
Notice odors from hot wires, motors, burning rubber, etc. Don’t
sniff around batteries or inhale smoke.
Feel for components that may have gotten warm. Watch for
burns.
Trouble Shooting Do’s and Don’ts
continued
Do know what conditions were present at the time of the failure
9.
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Does it happen at max power going head to head with other robots?
Was the robot in a collision with another robot or field piece?
Is the failure repeatable or seemingly random?
Is the severity or rate of occurrence increasing or decreasing?
What events were coincident with the failure (shipping damage, new
battery, spilled Pepsi, etc.
Don’t have more people’s hands in the robot than is necessary
Do try to duplicate the failure mode in a “controlled environment”
to confirm that you have the true root cause.
Do take measurements (current draw under load, voltage drop,
continuity) before disassembly, adjustments, or repairs are
attempted.
Trouble Shooting Do’s and Don’ts
continued
13.
14.
Don’t begin to implement corrective actions before you have
determined the root cause.
Do try to duplicate the failure mode after the corrective actions
are in place to verify your fix.
Helpful Tools and Materials for
Analysis and Corrective Actions
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Multimeter capable of indirect current measurement. Very useful.
Available for under $200 from Newark Electronics.
Electrical connector crimping tools, soldering gun, tape, and
assorted wiring connectors and wire.
Spare kit parts: spikes, victors, control cables, motors, etc.
Spare parts that were custom built and critical to the drive system.
Tie wraps and velcro
Thermocouples to measure motor temperatures under heavy use.
Robot dynamometer. If you don’t have one, you can use ours.
Corrective Action Implementation
1. Emergency corrective actions (containment)
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Can you “contain the issue” to get you through the next match
(tie wraps, braces, screws, jumper in a new component, etc.)?
Can you remove or deactivate the damaged component and play
the round without it until it is fixed?
Can you continue to run with the problem without causing more
serious or permanent damage?
2. Long term corrective actions
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Accidental damage:
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Can a reoccurrence be prevented by adding protection (a guard,
shield, or modification) ?
Craftsmanship problem:
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After correcting a craftsmanship problem, check to see that there are
not additional areas. Don’t just fix the failed crimp, check all crimps.
Corrective Action Implementation
Continued
Long term corrective actions cont’d.
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Design flaw:
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Is it possible to eliminate or reduce the severity of the
problem with a change to design, software, or driving style?
3. Avoiding collateral damage during analysis / repair
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Remove or protect sensitive components (victors, spikes,
controller, etc.) from debris or damage during repairs with
a towel, etc.
Don’t lean on or reach over the robot, walk around it.
Do not place tools, heavy components, or drinks on the
robot.
Corrective Action Implementation
Continued
4. Verifying the fix

Can the problem be reproduced after the “fix”
has been incorporated?
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Are any of the previous symptoms still
present (noises, hot wires, low power, etc.)?
DFMEA
(Design Failure Mode and Effects Analysis)
Note: This is an analysis tool that is used during the design stage.
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List all known possible design failure modes
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Let’s use a real example: drive chain breaks
Estimate probability (what are the chances of it happening).
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It is likely to happen: high probability (it did)
Assess the level of severity if it happened (the affects)
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If it happens, we loose power to that wheel
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What secondary failure modes might be caused by the
primary failure mode.
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The broken chain might get tangled up in the wheel and lock
it up. It might also get tangled up in the other drive chain.
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What is that probability and severity?
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A tangled chain could bind a wheel and could break a hub.
Address problems with the highest probability and severity first.
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Monitor and maintain the chain tension (didn’t do this at first)
and remove any threat of entanglement at the wheel. (did this)
Design for Reliability and
Durability
1. Apply the KISS principle (keep it simple, silly)
2. Don’t design in cascading failures (like in our
example)
3. Layout your wiring neatly and in a naturally protected
area. If it must be routed in a severe area, protect it.
4. Label both ends of each wire, both power circuits and
control cables. This will assist you in diagnosing
issues and will save you time in the long run.
5. Protect exposed components from damage with metal
guards or lexan.
6. Positively secure your battery in the robot and tie wrap
the power cables together prior to each match. In
every regional at least one robot has a battery fall out.
Design for Reliability and
Durability
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Use self aligning bearings and couplers that allow for
misalignment in the build or frame deflection.
Anticipate sudden shock loads from accidental
contact at any angle. Severe side impacts can cause
a drive chain to jump off of the sprockets.
Loctite* all set screws in place
Include a method for adjusting drive track tension to
account for track stretch or wear.
Include a method for adjusting drive chain tension.
Include guides for long drive chains to keep them
from falling off of sprockets
#25 pitch chain is lighter, but much less robust than
#35 chain
Craftsmanship
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Wiring
1. Terminals must be properly crimped to achieve a solid
mechanical and electrical connection. Do a pull test on
several of your samples. Crimping is the chief source of
problems.
2. Terminals need to be the proper size and screwed down tight
at the device.
3. Make sure you meet or exceed the wire gauge sizes specified.
4. Make sure wiring is not routed over sharp edges, in pinch
zones, or areas where it will be bruised, stretched, or cut.
5. Soldering of terminals should not be necessary if they are
crimped properly. Soldering can temporarily mask a poorly
crimped terminal.
6. When routing wiring through tubing, or in any enclosed area,
be careful not to drill through it.
7. Check for continuity from the battery to the frame (grounding
out). before powering up your robot for the first time.
Craftsmanship
Construction:
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Break sharp edges that can damage wires, cut
tires, cause mechanisms to bind, or cause personal
injury.
Build things true and square that need to be true
and square: axles, motors, etc. Not everything
needs precision.
Be careful not to weaken high stress areas during
the “weight loss” phase of the program.
In general, follow sound building practices
Inspection and Maintenance
1. Create an inspection check list to go over every time
the robot returns from a match to find damage &
wear.
2. Exercise all robot features for proper function after the
robot has been: shipped, idle overnight, repaired,
modified, etc.
3. Keep a log of all repairs and modifications to your
robot: damage, wear, regular service, modifications,
etc.
4. Establish a battery maintenance and charging
procedure with one person assigned to be in charge.
Team 494 Robot
Dynamometer
Reliability and Trouble Shooting
Drive Systems
Questions?
This presentation will be posted on the Martian website:
www.494martians.com