mindstorms mayhem - 2005con building fll robots
TRANSCRIPT
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
1/51
Building FLL RobotsApril 22, 2005
Nathan Gray
FRC Team #1519
Mechanical Mayhemwww.mechanicalmayhem.org
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
2/51
April 22, 2005 Mechanical Mayhem 2
Objective of this talk
To teach sound building fundamentals for
FIRST LEGO League robots
Some discussion may not be applicable
to general purpose robots
Assuming the usual FLL parts restrictions
Assumng a vinyl mat on a 4x8 table with
2x4 walls will be used again next year
And so on
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
3/51
April 22, 2005 Mechanical Mayhem 3
Contents
Robot Components Overview
Robot Design Options
Common Robot Issues Robot Design Goals
Dynamic Environment
Some Robust Techniques Examples
Resources
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
4/51
April 22, 2005 Mechanical Mayhem 4
Components Overview
Technic beams and plates
Pins and axles
RCX Microcontroller
Motors
Sensors Gears, Pulleys, Wheels
Special pieces
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
5/51
April 22, 2005 Mechanical Mayhem 5
Technic beams and plates
STandard Unit ofDimension is a STUD
Six studs = fivebeams, so beams are6/5 (or 1.2) studs high
Three plates = onebeam, so plates are
0.4 studs high
Hole spacing is thesame as stud spacing
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
6/51
April 22, 2005 Mechanical Mayhem 6
Pins and axles
Many various kinds Pin, friction pin, and long
variants
Evil, super friction pin that
looks very similar to thenormal friction pin
Axles, come in variousnumbers of studs
Never bend axles! Axlesholding wheels or gearsshould be closely supportedon both sides
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
7/51
April 22, 2005 Mechanical Mayhem 7
RCX Microcontroller
3 outputs for motors or lamps
3 inputs for sensors
RCX v1.0 has a power adapter input
(which isnt generally used for FLL)
Any of RCX versions 1.0, 1.5, 2.0 are
fine for FLL Use the latest RIS or
RoboLab software on all of them
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
8/51
April 22, 2005 Mechanical Mayhem 8
Motors
There are several different kinds, but
FLL allows three 9 volt geared grey motors
Caution! Two different kinds of grey geared 9volt motors look very similar
The newer version is much lighter, but slightly
slower and less powerful
For great info on LEGO motors, see
http://www.philohome.com/motors/motorcomp.htm
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
9/51
April 22, 2005 Mechanical Mayhem 9
Sensors
FLL allows
Two light sensors that measure 0-100% light
typical FLL table measurements are approximately30-60
Two touch sensors which can be used as bumper
sensors or limit switches
One rotation sensor Measurement granularity is 1/16 of a rotation
Can give bad data if very fast or very slow
Rotational speed near motor speed is fine (200-400 rpm)
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
10/51
April 22, 2005 Mechanical Mayhem 10
Sensors (continued)
Use all the permitted sensors!
Can stack touch sensors on top of light
sensor inputs A closed touch switch reads 100% brightness Cannot read 100% otherwise, unless pointed at
light source
Good sensor information at: http://www.plazaearth.com/usr/gasperi/lego.htm
Note: homebrew sensors are not FLL legal
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
11/51
April 22, 2005 Mechanical Mayhem 11
Gears
Transfer rotation from one axle to another
Even number of gears reverses the direction ofrotation
The radii determine gear spacing, transferred speed,and power
Inverse relationship between power and speed
There are lots of gear spacing issues beyond thescope of this talk
Special half-stud beams or diagonal spacing sometimes help An eight tooth gear has a diameter equal to one stud
8, 24, and 40 tooth gears work well together because theirradii are all multiples of 0.5
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
12/51
April 22, 2005 Mechanical Mayhem 12
Gears (continued)
Worm gears
Are effectively one tooth gears
Significant efficiency lost to friction Since they cant be back driven, they are
great for arms that should hold theirposition
Some good gear info at http://www.owlnet.rice.edu/%7Eelec201/Bo
ok/legos.html
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
13/51
April 22, 2005 Mechanical Mayhem 13
Pulleys Work like toothless gears
All the same radius principles apply
Spacing is more flexible than gears Can be useful when want to allow slip
Higher frictional load than gears or
chain, and belts can stretch and break Try to use gears instead
Use a clutch gear if necessary
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
14/51
April 22, 2005 Mechanical Mayhem 14
Wheels
Like pulleys and gears, the wheel dimensionis key!
Think of the wheel as the final gear in the
drive train Larger wheels will make the robot move faster,
with less power
With stability, traction, turning agility, and so
on, there are lots of trade-offs in choosingwheels
See the LEGO tire traction tests at: http://www.philohome.com/traction/traction.htm
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
15/51
April 22, 2005 Mechanical Mayhem 15
Special pieces
1x1 beam, and double-hole 1x2beam, can be used to get halfstud spacing
Clutch gears: protects motorsand LEGO from self-destruction
U-joints: can be used when astraight axle just wont do Should always be used in pairs
Original and final shaft shouldbe parallel
Worm gearbox the perfect
thing to raise and lower an arm Chain achieves some of theflexibility of pulleys, but moreprecise, efficient, and reliablethan belts
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
16/51
April 22, 2005 Mechanical Mayhem 16
Robot Design Options
Drive systems
Modular vs. Monolithic Robots
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
17/51
April 22, 2005 Mechanical Mayhem 17
Robot Drive Systems
Dual motor / wheel differential drive is a good (andcommon) choice for FLL Important to have well-matched motors!
Treaded skid steer / tank drive can sometimes beuseful for ATV missions Very stable, but usually slow and sometimes hard to
navigate accurately
Active steering (e.g., like a car) has some attractivefeatures, but: Might require a dedicated motor
Cannot spin in place
Legs?
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
18/51
April 22, 2005 Mechanical Mayhem 18
Modular versus Monolithic?
A modular robot is a core robot withattachments that snap on at specificinterface points e.g. might have a
different attachment for each FLLmission
A monolithic (or self-contained) robothas no (or very few) attachments that
go on or come off the robot. Either approach can be very successful!
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
19/51
April 22, 2005 Mechanical Mayhem 19
Monolithic Considerations Purpose built for each years missions
Fewer parts to bring to the competition table
Fewer attachments create fewer opportunities for
operator errors Fewer attachments mean less time spent in base,
and more table time available for the robot to actually
accomplish the missions
Might be easier / better to solve particular missionswith dedicated robot features rather than an
attachment that uses a standardized interface
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
20/51
April 22, 2005 Mechanical Mayhem 20
Modular Considerations
Dont necessarily need to redesign everythingevery year
Can accumulate libraries of reusable code for
the core robot base Easy to prototype new ideas
Attachments can be used interchangeably onduplicate robot bases
Student sub-groups can develop separateattachments in parallel without interfering withother mission solutions
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
21/51
April 22, 2005 Mechanical Mayhem 21
Common Robot Issues
Robot could fall apart at a bad time
It may not drive straight
Robot might get lost on the table
Maybe it is inconsistent and does
something slightly different every time
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
22/51
April 22, 2005 Mechanical Mayhem 22
Robot design goals
Simple: easy to replicate and less to go wrong! Ask: Is there an easier solution?
Robust: dont want robots falling apart on the table!
Compact Small enough to turn in tight spaces
Keep the center of gravity between the wheels
Wire routingtuck wires in so they dont get pulled loose
Predictable and reliable Behavior should be consistent and repeatable
Aesthetics: its nice to have a good looking robot!
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
23/51
April 22, 2005 Mechanical Mayhem 23
Some Robust Techniques
Shielding light sensors
Solid construction
Using good batteries
Going straight (enough)
Reliable Navigation
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
24/51
April 22, 2005 Mechanical Mayhem 24
Dynamic Environment
Even with good design, construction andprogramming, there can still be problems
FLL robots and programs are generallydesigned assuming a well known (static)environment without any interference
Unfortunately, things do change: sunlight,
spotlights, camera flashes, dust on the tablesand wheels, the battery power level, etc
There are ways to mitigate some of these
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
25/51
April 22, 2005 Mechanical Mayhem 25
Shielding Light Sensors
You cannot control ambient light, but
You can control what the sensor sees
Build a light box, or other light barrier,
around the light sensors
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
26/51
April 22, 2005 Mechanical Mayhem 26
Solid Construction
Use cross-bracing and vertical ties
Connect enough studs use significant
overlap
Use plates to lock the alignment of
beams
Mount motors and sensors securely
Tie down sensor and motor wires
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
27/51
April 22, 2005 Mechanical Mayhem 27
Using Good Batteries
Important! Battery levels can affect
robot behavior in many ways!
Experiment with both strong and weak
batteries
Know you batterys discharge behavior
We like Sanyo NiMH rechargeables
Alkaline have more initial power, but
consistency is usually more important
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
28/51
April 22, 2005 Mechanical Mayhem 28
Going Straight
Use matched motors (especially if
differential drive)
Matched frictional drag minimize dragon both sides
Uniform weight distribution
Front guide wheels that roll straight (butthat will slip sideways when necessary)
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
29/51
April 22, 2005 Mechanical Mayhem 29
Three levels of Navigation
Dead reckoning
e.g. aim and shoot for time
Odometry / counting rotations e.g. aim and shoot for wheel spins
Feedback orientation
Use walls, mat, field elements so the robotknows where it is on the table
Self correcting, no jigs or precise starts
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
30/51
April 22, 2005 Mechanical Mayhem 30
Feedback Orientation Sites
Can frequently run a wheel along a wall
Turns parallel to a wall can sometimes align
on the perpendicular wall Look for reliable attack points:
Intersections of linear table features, e.g. wall
corners, line intersections, other mat features
Field element corners can also be used foralignment
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
31/51
April 22, 2005 Mechanical Mayhem 31
Sample MAYHEM Robot Core
Similar to one used for City Sights
Missing sensors, weights, and
standardized power take off interface,as compared to current robot core base
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
32/51
April 22, 2005 Mechanical Mayhem 32
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
33/51
April 22, 2005 Mechanical Mayhem 33
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
34/51
April 22, 2005 Mechanical Mayhem 34
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
35/51
April 22, 2005 Mechanical Mayhem 35
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
36/51
April 22, 2005 Mechanical Mayhem 36
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
37/51
April 22, 2005 Mechanical Mayhem 37
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
38/51
April 22, 2005 Mechanical Mayhem 38
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
39/51
April 22, 2005 Mechanical Mayhem 39
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
40/51
April 22, 2005 Mechanical Mayhem 40
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
41/51
April 22, 2005 Mechanical Mayhem 41
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
42/51
April 22, 2005 Mechanical Mayhem 42
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
43/51
April 22, 2005 Mechanical Mayhem 43
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
44/51
April 22, 2005 Mechanical Mayhem 44
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
45/51
April 22, 2005 Mechanical Mayhem 45
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
46/51
April 22, 2005 Mechanical Mayhem 46
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
47/51
April 22, 2005 Mechanical Mayhem 47
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
48/51
April 22, 2005 Mechanical Mayhem 48
Sample MAYHEM attachments
Rover retriever
Crater transmission
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
49/51
April 22, 2005 Mechanical Mayhem 49
Where to get LEGO?
Ebay
Look up set parts on:
www.peeron.com
PITSCO LEGO Dacta:
www.legoeducationstore.com
Bricklink: www.bricklink.com
The LEGO Group store: www.lego.com
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
50/51
April 22, 2005 Mechanical Mayhem 50
Other Resources
Excellent building guide from Minnesota INSciTE,hightechkids.org -- search for Building LEGO RobotsFor FIRST LEGO League by Dean Hystad
Tons of info at LEGO Mindstorms Internals: www.crynwr.com/lego-robotics/
The Ferraris book: Building Robots with LEGOMindstorms
Comprehensive FLL Coachs Handbook at http://www.fll-freak.com
Mikes LEGO Cad: http://www.lm-software.com/mlcad
-
7/31/2019 Mindstorms Mayhem - 2005CON Building FLL Robots
51/51
April 22 2005 Mechanical Mayhem 51
Summary
Probably want to use dual motor /
differential drive
Probably want to use gears (especially8, 24, and/or 40 tooth gears)
Use vertical ties and cross bracing
Have a reliable plan for navigation