Compilation of approaches used for FIRST robotics game piece manipulating systems. Will briefly discuss pro’s, con’s and design trade offs for a number of different manipulator designs.
3. Hanging
Manipulate How ?
Game objectives change each year
Lifting Dumping
Throwing
Kicking Gathering
4. Stuff That Don’t Work
Know the possibilities Things that Manipulate
Look on line, at competitions
Manipulators that
Talk to mentors, teams
work for the game
This seminar
Know the Objectives
Game pieces
Game & robot rules
Your game strategy
Your
Design
Know your capabilities
Tools, Skills, Materials,
Manpower , Budget , Time Manipulators you
can build
Don’t be this team
5. Many Types of Manipulators
Heavy lifting / Long reach Reoccurring
o Articulating Arms
o Parallel arms
themes in FIRST
o Telescoping Lifts games
Grippers
o Rollers
o Clamps
o Claws FIRST definition for
Collect and Deliver a manipulator:
o Accumulators & Conveyers
o Turrets
o Shooters & Kickers
o Buckets & Tables
Device that
Power & Control moves the game
o Winches piece from where
o Brakes
o Latches it is to where it
o Pneumatics
o Springs and Bungee
needs to be
o Gears & Sprockets
7. Torque: Angle and Distance
Torque = Force x Distance
o Same force, different angle = different torque
o Measure from the pivot point
o Motor & gearing must overcome torque W= 10 lbs
o Maximum torque at 90 degrees
Torque = W x D Torque = W x D/2
W=10 lbs
1/2 D
D
8. Power: Torque and Speed
Power determines how fast you can move things
Power = Torque / Time or Torque x Rotational Velocity
Same torque with 2x Power = 2x Speed
Or twice the arm length at same speed ….
3 ft
Power 10 lbs 20 lbs
10 lbs trade 30 ft-lbs 60 ft-lbs
offs
425 100 RPM 50 RPM
Power limits arm length. Watts 1.6 rps .83 rps
Probably don’t want a 10 ft arm 42.5 10 RPM 5 RPM
whipping around at 1000 RPM Watts .16 rps .08 rps
anyway…
9. Arm Design Tips
Lightweight Materials: tubes, thin wall
Watch elbow and wrist weight at ends of arm
Sensors for feedback & control
limit switches, potentiometers, encoders
Linkages help control long arms
KISS your arm
Less parts… to build or break
Easier to operate
More robust
Counterbalance
Spring, weight, pneumatic, bungee…
Calculate the forces
Watch out for Center of gravity
Sideways forces when extended
Model the reach & orientation
10. Telescoping Lifts
Extension Lifts
Motion achieved by stacked members sliding on each other
Scissor Lift
Motion achieved by “unfolding” crossed members
11. Extension Lift Rigging
Continuous Cascade
The final stage moves up
first and down last.
Previous stage speed plus
own speed
o Power vs. speed
equations apply. Don’t
underestimate the power.
o Often needs brakes or
ratchet mechanism
12. Cascade Rigging
Up-pulling and down-pulling
cables have different speeds
Different cable speeds can be Slider
handled with different drum (Stage3)
diameters or multiple Pulleys
Intermediate sections don’t jam
Stage2
– active return
High tension on the lower
stage cables Stage1
Base
13. Continuous Rigging
Slider
Cable goes same speed for (Stage3)
up and down pulling cables
Intermediate sections
sometimes jam
Stage2
Lower cable tension
More complex cable routing
Stage1
Base
14. Continuous Rigging Internal
Pull-down cable routed back on
reverse route as pull-up cable
Most complex cable routing Slider
All stages have active return (Stage3)
Cleaner and protected cables
Stage2
Stage1
Base
15. Extension Lift Design tips
Use cables to drive up AND
down, or add a cable recoil
device
Segments must move freely
Cable lengths must be adjustable
Minimize slop and free-play
Maximize segment overlap
20% minimum
More for bottom, less for top
Stiffness and strength needed
Heavy system, overlapping parts
Minimize weight, especially at top
16. Arms vs. Lifts
Feature Arm Lift
Reach over object Yes No
Fall over, get up Yes, if strong enough No
Complexity Moderate High
Weight capacity Moderate High
Go under barriers Yes, fold down Maybe, limits lift height
Center of gravity () Cantilevered Central mass
Operating space Large swing space Compact
Adding reach Difficult. More Easier.
articulations More lift sections
Combinations Arm with extender Lift with arm on top
17. Combination Example:
Continuous direct drive chain
runs stage 1 up and down
No winch drum needed
Cascade cable lifts slider stage
Gravity return
Got away with this only
because slider GOG very
well balanced on first stage
Telescoping arm with wrist on
slider stage to reach over objects
2471 in 2011
18. Get a Grip
FIRST definition of a gripper:
Device that grabs a game object
…and releases it when needed.
Design Concerns Methods
Getting object into grip Pneumatic claws /clamps
Hanging on 1 axis
2 axis
Speed of grip and release
Motorized claw or clamp
Position control
Rollers
Weight and power source Hoop grips
If at end of arm
Suction
20. Pneumatic: 2 and 3 point clamps
Pneumatic Cylinder
extends & retracts linkage
to open and close gripper
Combined arm and gripper
Easy to manufacture
Easy to control
Quick grab
Limited grip force
Use 3 fingers for 2-axis grip 968 in 2004
60 in 2004
21. Motorized clamp
Generally slower
May be too slow for
frequent grips
Okay if few grabs per
game of heavy objects
More complex (gearing
& motors)
Heavier
Tunable force
No pneumatics
49 in 2001
22. Suction Grips
Needs vacuum generator
Uses various cups to grab
Slow
Not secure
Not easy to control
Simple
Subject to damage of
suction cup or game pieces
Not recommended for
heavy game pieces
Used successfully to hold
soccer balls for kickers
(Breakaway 2010)
23. Roller grips
Allows for misalignment when
grabbing
Won’t let go
Extends object as releasing
Simple mechanism
Have a “full in” sensor
Many possible variations
Mixed roller & conveyer
45 in 2008
Reverse top and bottom roller
direction to rotate object
148 in 2007
24. Counter Rotating Methods
Crossed round belts
Many ways to achieve counter
rotating shafts. Here are few
configurations that can run off a
single motor or gearbox.
Could also drive each shaft with
own motor
Counter
Stacked pulleys rotating
on single drive gearbox
shaft
25. Gripper design
Hang On!
High friction needed
Rubber, neoprene, silicone, sandpaper … but don’t damage game object
Force: Highest at grip point
Force = 2 to 4 x object weight
Use linkages and toggles for mechanical advantage
Extra axis of grip = More control
The need for speed
Wide capture window
Quickness covers mistakes
Quick to grab , Drop & re-grab
Fast : Pneumatic gripper. Not so fast: Motor gripper
Make it easy to control
Limit switches , Auto-functions
Intuitive control functions
Don’t make driver push to make the robot pull
26. Rotating Turrets
Tube or post (recommended)
Lazy Susan (not for high loads)
Know when it is needed
o One Goal = good
o Nine Goals = not so good
o Fixed targets = good
o Moving targets = not so good
Bearing structure must be solid
Rotation can be slow
Include sensor feedback
o Know which way it is pointing
27. Accumulator: Rotational device that collects objects
Horizontal rollers: gathers balls from floor or platforms
Vertical rollers: pushes balls up or down
Wheels: best for big objects
Can use to dispense objects out of robot
Pointing the robot is aiming method in this case
28. Conveyers: For moving multiple objects
Point to point within your robot
When game involves handling
many pieces at once
Why do balls jam on belts?
- Stick and rub against each other as they
try to rotate along the conveyor
Solution #1
- Use individual rollers
- Adds weight and complexity
Solution #2
- Use pairs of belts
- Increases size and complexity
Solution #3
- Use a slippery material for the non-moving
surface (Teflon sheet works great)
30. More control is better
Avoid gravity feeds – these are slow and will jam
Direct the flow: reduce “random” movements.
Not all game objects are created equal
Tend to change shape, inflation, etc
Building adaptive/ flexible systems
Test with different sizes, inflation, etc.
Speed vs. Volume
Optimize for the game and strategy
The more capacity, the better
32. Secure shooting structure = more accuracy
Feed balls individually, controlling flow
Rotating tube or wheel
One wheel or two counter rotating 1771 in 2009
High speed & power: 2000-4000 rpm
Brace for vibration
Protect for safety
Turret allows for aiming
Sensors detect ball presence
& shot direction Note Circular
Conveyer. One
roller on inside
cylindrical rolling
surface outside
33. Use for dumping many objects
Integrate with your accumulator
and conveyer
Heavy ones may move too slow
Usually pneumatic powered but
can run with gear, spring or winch
488 in 2009
34. 2010
Many uses
Hanging Robots: 2000, 2004, 2010
Lifting Robots: 2007
Loading kickers 2010
Great for high torque applications
Fits into limited space
Easy to route or reroute
Good Pull. Bad Push 2004
35. Capture
the
cable
Secure the cable routing
Smooth winding & unwinding
Leave room on drum for wound up cable
Guide the cable
Return cable or spring
Must have tension on cable to unwind
Can use cable in both directions Guide
Spring or bungee return the Maintain
Gravity return (not recommended) cable Tension
Calculate the torque and speed
Use braking devices
Brake or ratchet
36. Sudden release of power
Use stored energy:
Springs Bungee, Pneumatic
Design & test a good latch
mechanism
Secure lock for safety
Fast release
1 per game deployments
2011 minibot release
37. Hooking and latching devices used to
grab goals, bars, and other non-
scoring objects
Hold stored power in place
Spring or bungee power
Several ways: Self latching wheel lock
Hooks
Locking wheels
Rollers Basic Automatic Latch
Pins
Bevel for self latching
Springs Removable safety pin
Small release force
at end of lever
Strong pivot in
Spring line with large
return and force being held
stop
38. Start design early. Latches tend to be afterthoughts but
are often a critical part of the operation
Don’t depend on driver to latch, use a smart mechanism
Spring loaded (preferred)
Sensor met and automatic command given
Use operated mechanism to let go, not to latch
Have a secure latch
Don’t want release when robots crash
Be able to let go quickly
Pneumatic lever
Motorized winch, pulling a string
Cam on a gear motor
Servo (light release force only)
Don’t forget a safety pin or latch for when you are
working on the robot
39. Look around see what works and does not work
Know your design objectives and game strategy
Stay within your capabilities
Design before you build
Calculate the forces and speeds
Understand the dimensions using CAD or a model
Keep it simple
Make it well
Poor craftsmanship can ruin the best design
Analyze for failure points.
Use to refine design and decide on spare parts
Have fun
40. Many thanks to teams and companies who made
materials for this presentation freely available on
web sites to help FIRST students.
Andy Baker : Team 45
Jason Marr : Team 2471
Wildcats: Team 1510
The Flaming Chickens: Team 1540
Society of robots
http://www.societyofrobots.com/mechanics_gears.shtml
Andy Baker’s original presentation and inspiration for this
seminar is available on line
There are many examples and resources available. Be
sure to use them for your robot designs.
42. Motor Power:
Assuming 100% power transfer efficiency:
All motors can lift the same amount they just do it at
different rates.
No power transfer mechanisms are 100% efficient
Inefficiencies due to friction, binding, etc.
Spur gears ~ 90%
Chain sprockets ~ 80%
It adds up!
2 spur gears + sprocket =
Worm gears ~ 70%
.9 x.9 x.8 = .65
Planetary gears ~80%
Losing 35% of power to the drive train
Calculate the known inefficiencies and then design in a
safety factor (2x to 4x)
Stall current can trip the breakers
43. Parallel Arms
• Pin loading can be very high
• Watch for buckling in lower arm
• Has limited range rotation
• Keeps gripper in fixed orientation
44. Scissor Lifts
Advantages
Minimum retracted height - can go
under field barriers
Disadvantages
Tends to be heavy when made
stable enough
Doesn’t deal well with side loads
Must be built very precisely
Stability decreases as height
increases
Stress loads very high at beginning
of travel
Not recommend without prior
experience
45. Pneumatic latch, solidly
grabs pipe
Force and friction only
No “smart mechanism”
Spring-loaded latch
Motorized release
Smart Mechanism
469 in 2003
47. Ratchet - Complete lock in one direction in discrete increments
Clutch Bearing - Completely lock in one direction any spot
Brake pads - Squeezes on a rotating device to stop motion - can lock in
both directions. Simple device
Disc brakes - Like those on your mountain bike
Gear brakes - Apply to lowest torque gear in gearbox
Belt Brake- Strap around a drum or pulley
Dynamic Breaking by motors lets go when power is lost.
Use for control, but not for safety or end game
Gearbox that cannot be back-driven is usually an inefficient one.