Difference between revisions of "RC08-Dribbler"

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This page contains the information and documentation of the 2008 dribbler system
 
This page contains the information and documentation of the 2008 dribbler system
  
−
[RobocupMechanical|Robocup 2008 Mechanical]
+
==Assembly Structure==
 +
{| border="1" cellpadding="2"
 +
!width="225"|PART NAME
 +
!width="100"|PART NUMBER
 +
!width="50"|QUANTITY
 +
|-
 +
|Mounting Block || RC-2008-04-01 || 2
 +
|-
 +
|-
 +
|Swing|| RC-2008-04-02 || 2
 +
|-
 +
|-
 +
|Motor Plate || RC-2008-04-03 || 1
 +
|-
 +
|-
 +
|Standoff || RC-2008-04-04 || 2
 +
|-
 +
|-
 +
|Hinge Shaft || RC-2008-04-05 || 1
 +
|-
 +
|-
 +
|8-32 Lock Nut || RC-2008-04-06 || 4
 +
|-
 +
|-
 +
|2" Hex Standoff|| RC-2008-04-07 || 1
 +
|-
 +
|-
 +
|Dribbler Motor || RC-2008-04-08 || 1
 +
|-
 +
|-
 +
|M2x5 Screw || RC-2008-04-09 || 2
 +
|-
 +
|-
 +
|Dribbler Motor Gear || RC-2008-04-10 || 1
 +
|-
 +
|-
 +
|6-32 x 3/4 Screw || RC-2008-04-11 || 1
 +
|-
 +
|-
 +
|Cross Plate || RC-2008-04-12 || 1
 +
|-
 +
|-
 +
|4mm Snap Bearing|| RC-2008-04-13 || 2
 +
|-
 +
|-
 +
|Dribbler Shaft || RC-2008-04-14 || 1
 +
|-
 +
|-
 +
|Dribbler Roller || RC-2008-04-15 || 1
 +
|-
 +
|-
 +
|Dribbler Roller Gear || RC-2008-04-16 || 1
 +
|-
 +
|-
 +
|Left Torsion Spring || RC-2008-04-17 || 1
 +
|-
 +
|-
 +
|Right Torsion Spring || RC-2008-04-18 || 1
 +
|-
 +
|-
 +
|6-32 x 1/4 Screw || RC-2008-04-19 || 1
 +
|-
 +
|-
 +
|3/8" Washer || RC-2008-04-20 || 1
 +
|-
 +
|-
 +
|Neoprene Rubber Tube || RC-2008-04-21 || 1
 +
|-
 +
|-
 +
|4-40 Set Screw|| RC-2008-04-22||1
 +
|-
 +
|}
  
−
==Motor==
 
−
*Need to still find motor - something with short lead time, possibly a hobby store
 
−
*places to look
 
−
**[http://www.pittmannet.com/quick_index.html#brush Pittman ]
 
−
**[http://www.horizonhobby.com/ Horizon Hobby]
 
  
−
==Gearing==
+
==Parts & Components==
−
*Example geared down dribbler bar speed used in CMU robots ~7800 RPM
+
===Motor===
 +
Fleet motor from Maxon
 +
*Part no: 266521 with attached gear head 118184.
 +
*5.4 gear reduction
 +
*cost: $146.20 each
 +
*[http://test.maxonmotor.com/docsx/Download/catalog_2007/Pdf/07_154_e.pdf Motor Data Sheet]
 +
*[http://test.maxonmotor.com/docsx/Download/catalog_2007/Pdf/07_215_e.pdf Gearhead Data Sheet]
  
−
==Dribbler bar==
+
 
 +
Vendor: MicroMo
 +
* Motor: 12V DC brushless servo motor #E-1628B
 +
**$147.10 each
 +
* Planetary gearhead: #E-167 gear reduction: 14
 +
* Complete assembly 1628-V-0003
 +
Cost: $200.40 each
 +
 
 +
* [http://www.micromo.com/ MicroMo]
 +
* [http://www.micromo.com/uploadpk/e_1628B_MIN.pdf Motor Data Sheet]
 +
* [http://www.micromo.com/uploadpk/e_167_MIN.pdf Gearhead Data Sheet]
 +
 
 +
* Electrical specification
 +
** 12 Volts
 +
** must have position or speed encoders
 +
** brushless DC
 +
 
 +
*Maxon motor, the same CMU uses, was chosen for the fleet. This was based on 4wk shorter lead time, $60 cheaper  per motor, and significantly greater performance as can be seen from the figures generated by a Matlab script
 +
[[image:motor_comparison.jpg|800 px|Dribbler motor comparison]]
 +
 
 +
===Gears===
 +
=====Motor gear=====
 +
:Vendor: SDP/SI
 +
:Part No.: A 1B 2MYK05035
 +
:Description: Module 0.5, 35 Teeth, 20° Pressure Angle, Brass Gear with set screw, 3mm bore, 17.5mm PD
 +
:Cost: $7.47
 +
:Drawing:[https://sdp-si.com/eStore/..%5Css%5CPDF%5CSSUM7025.PDF Motor Gear Spec Sheet]
 +
*Connects directly to output of motor and powers dribbler roller
 +
 
 +
=====Roller gear=====
 +
:Vendor: SDP/SI
 +
:Part No.: A 1B 2MYK05025
 +
:Description: Module 0.5, 25 Teeth, 20° Pressure Angle, Brass Gear with set screw, 3mm bore, 12.5mm PD
 +
:Cost: $6.03
 +
:Drawing:[https://sdp-si.com/eStore/..%5Css%5CPDF%5CSSUM7025.PDF Dribbler Gear Spec Sheet]
 +
*Roller gear bore must be reamed out to 4mm
 +
*Powers the dribbler roller - is recessed into the roller itself
 +
 
 +
===Plates===
 +
=====Swing=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 8885K13
 +
:Description: Alloy 7075 Aluminum Sheet .063" Thick, 12" X 12"
 +
:Cost: $21.73
 +
*Contains the roller shaft, the motor mounts, spacers, and hinge shafts
 +
*Material is same and shared with Omniwheel plates
 +
*Left and right swings are identical
 +
 
 +
=====Motor plate=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 8885K13
 +
:Description: Alloy 7075 Aluminum Sheet .063" Thick, 12" X 12"
 +
:Cost: $21.73
 +
*Supports motor and connects to the 2 spacers in assembly
 +
*Material is same and shared with Omniwheel plates
 +
 
 +
=====Cross Plate=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 8885K13
 +
:Description: Alloy 7075 Aluminum Sheet .063" Thick, 12" X 12"
 +
:Cost: $21.73
 +
*Connects both mounting blocks and provides mechanical limitation for swing and torsion springs
 +
*Material is same and shared with Omniwheel plates
 +
 
 +
===Standoffs===
 +
=====Standoff=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 9062K271
 +
:Description: Alloy 6061 Aluminum Precision-Ground Rod 5/16" Diameter, 1' Length
 +
:Cost: $9.10
 +
*Standoff between swing and motor plate
 +
 
 +
=====2" Hex Standoff=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 91780A339
 +
:Description: Aluminum Female Threaded Hex Standoff 1/4" Hex, 2" Length, 6-32 Screw Size
 +
:Cost: $.88
 +
*Hex standoff between motor plate and swing
 +
*Both torsion springs anchor into the standoff
 +
 
 +
===Fasteners===
 +
=====6-32 x 1/4" socket cap screw=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 92220A141
 +
:Description: 6-32 x 1/4" steel, low profile, socket cap screw
 +
:Cost: $7.22 for 25
 +
*Connects the swing and hex standoff
 +
 
 +
=====6-32 x 3/4" socket cap screw=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 93615A217
 +
:Description: 6-32 x 3/4" 18-8 stainless steel, low profile, socket cap screw
 +
:Cost: $12.72 for 25
 +
*Connects the swing, motor plate, and hex standoff
 +
 
 +
=====8-32 Lock Nut=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 90633A009
 +
:Description: Steel Hex Nylon-Insert Locknut, 8-32 Screw Size, 11/32" W, 11/64" H
 +
:Cost: $2.21 each - STOCK
 +
*Constrains the dribbler and hinge shafts
 +
 
 +
=====4-40 Set Screw=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 91375A105
 +
:Description: Alloy Steel Cup Point Socket Set Screw 4-40 Thread, 3/16" Length
 +
:Cost: $7.99 for pack of 100
 +
*Pins dribbler roller to the dribbler shaft
 +
 
 +
===Shaft===
 +
=====Hinge shaft=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 8116K3
 +
:Description: A2 Tool Steel Tight-Tolerance Metric Rod 4 mm Diameter, 3' Length
 +
:Cost: $6.10
 +
*Joint between swings and mounting blocks
 +
 
 +
=====Dribbler shaft=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 8116K3
 +
:Description: A2 Tool Steel Tight-Tolerance Metric Rod 4 mm Diameter, 3' Length
 +
:Cost: $6.10
 +
*Roller and dribbler gear spin on dribbler shaft
 +
*Material is shared with the hinge shaft
 +
 
 +
===Springs===
 +
=====Left Torsion Spring=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 9271K35
 +
:Description: 1.375 lbf-in of torque. Music Wire Torsion Spring 90 Deg Angle, .309" Coil OD, .040" Wire, Cw/Lh, Packs of 6
 +
:Cost: $6.56 for 6
 +
*Left hand wound torsion spring
 +
*Rests on hinge shaft and provides cushioning for ball impact
 +
 
 +
=====Right Torsion Spring=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 9271K33
 +
:Description: 1.375 lbf-in of torque. Music Wire Torsion Spring 90 Deg Angle, .309" Coil OD, .040" Wire, Cw/Rh, Packs of 6
 +
:Cost: $6.56 for 6
 +
*Right hand wound torsion spring
 +
*Rests on hinge shaft and provides cushioning for ball impact
 +
 
 +
===Other===
 +
=====Mounting block=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 3511T11
 +
:Description: Alloy 6061 Aluminum Ground Flat Stock .250" Thick, 6" X 6" Size
 +
:Cost: $45.44 each - STOCK
 +
*Connects entire dribbler assembly to the robot
 +
 
 +
=====4mm snap thrust bearing=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 7817K33
 +
:Description: Metric Nylon Snap-in Thrust Bearing for 4mm Shaft Dia, 1.45-2.34 mm Sheet Metal Thick
 +
:Cost: $1.32 each
 +
*supports dribbler shaft in the swing
 +
 
 +
=====3/8" Washer=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 93286A009
 +
:Description: Aluminum washer 3/8" OD,.175" ID, 1/32" thick
 +
:Cost: $3.52 for 100
 +
*Washer between the swing and hex standoff
 +
 
 +
=====Neoprene Rubber Tube=====
 +
:Vendor: McMaster-Carr
 +
:Part No.: 7505K86
 +
:Description: Ultra-Flex Neoprene Rubber Heat-Shrink Tubing 3/4" Expanded ID, 3/8" Shrunken ID,
 +
:Cost: $8.97
 +
*Roller and dribbler gear spin on dribbler shaft
 +
*Material is shared with the hinge shaft
 +
 
 +
==Calculations==
 +
=====Torsion Spring=====
 +
* Analysis was done using the Work-Energy Principle with the assumption that the only work done is from the torsion spring and gravity. Because the dribbler assembly swings and has zero velocity at both positions, only the kinetic energy of the ball was used, at its maximum value of 10 m/s
 +
 
 +
=====Roller Speed=====
 +
* Gears were selected for a gear ratio lower than 2007. The 2008 ratio is 1.5. This was with the hope of having more torque available for the roller to grip the ball.
 +
 
 +
=====Dimensional Analysis=====
 +
* Using the Buckingham Pi theorem, an unknown function expressing the moment the dribbler roller puts on the ball based on other parameters was developed.
 +
* The inputs to this function can now guide the testing plan for the dribbler
 +
* The mom<math>f(mu)</math>
 +
[[Image:Dribblerdimension.png]]
 +
 
 +
==Notes==
 +
* 4mm steel shaft chosen to increase strength to prevent bending of dribbler shaft when hit with a ball
 +
*roller diameter - .5"
 +
*dribbler shaft still slides free in between two snap-in thrust bearings and can be removed to allow the roller to be changed out
 +
*several 4mm holes were widened to .170" holes to allow easy assembly with the 8-32 threaded shaft
 +
*it proved very difficult to even squeeze 4mm shaft through the thrust bearings
 +
*due to unknown errors a few addtional washers were placed in the assembly
 +
*on the left arm a small cut was created to allow the motor shaft to protrude
 +
*a new motor plate was created and fits flush to the motor
 +
*it was found when the original motor plate was attached and fastended, it would add a high amount of friction and actually stalled the motor
 +
*a big issue is that the 2 dribbler arms must be connected around either the back or the front - and not rotate independently
 +
*this independent rotation swivels the motor around, putting more stress and wear on the gears, or makes the gears not even mesh
 +
*the small standoff closest to the motor was replaced with a hex standoff, as it would hit the motor gear slightly if the motor was pushed up a bit
 +
*a 4mm die will be purchased to thread the shafts, preventing boring of 4mm holes
 +
 
 +
==Changes from Prototype==
 +
* a standoff now near the roller itself to provide structural stability, connect the two formerly independent swing arms, and protect the motor from ball impacts
 +
* clinch nuts will be used to anchor the assembly to the robot, making it much easier to remove the dribbler assembly
 +
* the motor mount plate now connects to the hinge axis, the motor, and the front standoff
 +
* the 4mm hinge and roller shafts will be threaded to fit 4mm hex nuts
 +
* the gear ratio between the motor and roller has increased from 1:1.4 to 1:1.75
 +
* the dribbler roller diameter has increased from .5" to 5/8"
 +
 
 +
 
 +
 
 +
==Dribbler bar prototypes==
 +
*shaft diameter on ends of bar - 3mm
 +
*maximum diameter of dribbler - .75"
 +
*the dribbler bar prototypes will be lathed and done coated with neoprene heat shrink
 +
[[image:dribblerprototype.png|500 px|Dribbler bar prototype drawing]]
 +
 
 +
===dribbler bar prototypes===
 +
*3/4" diameter aluminum bar stock
 +
**$8.34
 +
**McMaster part number 6750K181
 +
*3mm diameter aluminum bar stock
 +
**$6.94
 +
**McMaster part number 1681T21
 +
*3/4" neoprene heat shrink
 +
**pack of 5 for $8.97
 +
**McMaster part number 7505K86
 +
*3mm e-clips
 +
**pack of 100 for $3.03
 +
**McMaster part number 98543A101
 +
 
 +
==2007 Dribbler==
 +
===Drive gear===
 +
*attached to the motor
 +
*SDP/SI A-1B-2MYK05045 [https://sdp-si.com/eStore/..%5Css%5CPDF%5CSSUM7025.PDF Data sheet]
 +
*45 teeth, 3mm bore, 22.5mm pitch diameter
 +
===Dribbler gear===
 +
*attached to the roller. This is done by pressing having a set screw in the gear interfere with the roller. Both the gear and roller are free to spin on the shaft, which permitting easy change.
 +
*SDP/SI A-1B-2MYKO5020H [https://sdp-si.com/eStore/..%5Css%5CPDF%5CSSUM7025.PDF Data sheet]
 +
*20 teeth, 3mm bore, 10mm pitch diameter
 +
 
 +
*gear ratio from motor to drilbber = 2.25
 +
===Motor===
 +
*15.9mm diameter, 3mm output shaft
  
 
==Specs from CMU==
 
==Specs from CMU==
Line 29: Line 343:
  
 
*nominal dribbler bar speed = 28200/5.4*1.5 = 7833 RPM. It is, of course, adjustable by software.
 
*nominal dribbler bar speed = 28200/5.4*1.5 = 7833 RPM. It is, of course, adjustable by software.
 +
 +
[[Category: RC Mechanical]]
 +
[[Category:2007-2008]]

Latest revision as of 19:50, 24 May 2020

This page contains the information and documentation of the 2008 dribbler system

Assembly Structure

PART NAME PART NUMBER QUANTITY
Mounting Block RC-2008-04-01 2
Swing RC-2008-04-02 2
Motor Plate RC-2008-04-03 1
Standoff RC-2008-04-04 2
Hinge Shaft RC-2008-04-05 1
8-32 Lock Nut RC-2008-04-06 4
2" Hex Standoff RC-2008-04-07 1
Dribbler Motor RC-2008-04-08 1
M2x5 Screw RC-2008-04-09 2
Dribbler Motor Gear RC-2008-04-10 1
6-32 x 3/4 Screw RC-2008-04-11 1
Cross Plate RC-2008-04-12 1
4mm Snap Bearing RC-2008-04-13 2
Dribbler Shaft RC-2008-04-14 1
Dribbler Roller RC-2008-04-15 1
Dribbler Roller Gear RC-2008-04-16 1
Left Torsion Spring RC-2008-04-17 1
Right Torsion Spring RC-2008-04-18 1
6-32 x 1/4 Screw RC-2008-04-19 1
3/8" Washer RC-2008-04-20 1
Neoprene Rubber Tube RC-2008-04-21 1
4-40 Set Screw RC-2008-04-22 1


Parts & Components

Motor

Fleet motor from Maxon


Vendor: MicroMo

  • Motor: 12V DC brushless servo motor #E-1628B
    • $147.10 each
  • Planetary gearhead: #E-167 gear reduction: 14
  • Complete assembly 1628-V-0003

Cost: $200.40 each

  • Electrical specification
    • 12 Volts
    • must have position or speed encoders
    • brushless DC
  • Maxon motor, the same CMU uses, was chosen for the fleet. This was based on 4wk shorter lead time, $60 cheaper per motor, and significantly greater performance as can be seen from the figures generated by a Matlab script

Dribbler motor comparison

Gears

Motor gear
Vendor: SDP/SI
Part No.: A 1B 2MYK05035
Description: Module 0.5, 35 Teeth, 20° Pressure Angle, Brass Gear with set screw, 3mm bore, 17.5mm PD
Cost: $7.47
Drawing:Motor Gear Spec Sheet
  • Connects directly to output of motor and powers dribbler roller
Roller gear
Vendor: SDP/SI
Part No.: A 1B 2MYK05025
Description: Module 0.5, 25 Teeth, 20° Pressure Angle, Brass Gear with set screw, 3mm bore, 12.5mm PD
Cost: $6.03
Drawing:Dribbler Gear Spec Sheet
  • Roller gear bore must be reamed out to 4mm
  • Powers the dribbler roller - is recessed into the roller itself

Plates

Swing
Vendor: McMaster-Carr
Part No.: 8885K13
Description: Alloy 7075 Aluminum Sheet .063" Thick, 12" X 12"
Cost: $21.73
  • Contains the roller shaft, the motor mounts, spacers, and hinge shafts
  • Material is same and shared with Omniwheel plates
  • Left and right swings are identical
Motor plate
Vendor: McMaster-Carr
Part No.: 8885K13
Description: Alloy 7075 Aluminum Sheet .063" Thick, 12" X 12"
Cost: $21.73
  • Supports motor and connects to the 2 spacers in assembly
  • Material is same and shared with Omniwheel plates
Cross Plate
Vendor: McMaster-Carr
Part No.: 8885K13
Description: Alloy 7075 Aluminum Sheet .063" Thick, 12" X 12"
Cost: $21.73
  • Connects both mounting blocks and provides mechanical limitation for swing and torsion springs
  • Material is same and shared with Omniwheel plates

Standoffs

Standoff
Vendor: McMaster-Carr
Part No.: 9062K271
Description: Alloy 6061 Aluminum Precision-Ground Rod 5/16" Diameter, 1' Length
Cost: $9.10
  • Standoff between swing and motor plate
2" Hex Standoff
Vendor: McMaster-Carr
Part No.: 91780A339
Description: Aluminum Female Threaded Hex Standoff 1/4" Hex, 2" Length, 6-32 Screw Size
Cost: $.88
  • Hex standoff between motor plate and swing
  • Both torsion springs anchor into the standoff

Fasteners

6-32 x 1/4" socket cap screw
Vendor: McMaster-Carr
Part No.: 92220A141
Description: 6-32 x 1/4" steel, low profile, socket cap screw
Cost: $7.22 for 25
  • Connects the swing and hex standoff
6-32 x 3/4" socket cap screw
Vendor: McMaster-Carr
Part No.: 93615A217
Description: 6-32 x 3/4" 18-8 stainless steel, low profile, socket cap screw
Cost: $12.72 for 25
  • Connects the swing, motor plate, and hex standoff
8-32 Lock Nut
Vendor: McMaster-Carr
Part No.: 90633A009
Description: Steel Hex Nylon-Insert Locknut, 8-32 Screw Size, 11/32" W, 11/64" H
Cost: $2.21 each - STOCK
  • Constrains the dribbler and hinge shafts
4-40 Set Screw
Vendor: McMaster-Carr
Part No.: 91375A105
Description: Alloy Steel Cup Point Socket Set Screw 4-40 Thread, 3/16" Length
Cost: $7.99 for pack of 100
  • Pins dribbler roller to the dribbler shaft

Shaft

Hinge shaft
Vendor: McMaster-Carr
Part No.: 8116K3
Description: A2 Tool Steel Tight-Tolerance Metric Rod 4 mm Diameter, 3' Length
Cost: $6.10
  • Joint between swings and mounting blocks
Dribbler shaft
Vendor: McMaster-Carr
Part No.: 8116K3
Description: A2 Tool Steel Tight-Tolerance Metric Rod 4 mm Diameter, 3' Length
Cost: $6.10
  • Roller and dribbler gear spin on dribbler shaft
  • Material is shared with the hinge shaft

Springs

Left Torsion Spring
Vendor: McMaster-Carr
Part No.: 9271K35
Description: 1.375 lbf-in of torque. Music Wire Torsion Spring 90 Deg Angle, .309" Coil OD, .040" Wire, Cw/Lh, Packs of 6
Cost: $6.56 for 6
  • Left hand wound torsion spring
  • Rests on hinge shaft and provides cushioning for ball impact
Right Torsion Spring
Vendor: McMaster-Carr
Part No.: 9271K33
Description: 1.375 lbf-in of torque. Music Wire Torsion Spring 90 Deg Angle, .309" Coil OD, .040" Wire, Cw/Rh, Packs of 6
Cost: $6.56 for 6
  • Right hand wound torsion spring
  • Rests on hinge shaft and provides cushioning for ball impact

Other

Mounting block
Vendor: McMaster-Carr
Part No.: 3511T11
Description: Alloy 6061 Aluminum Ground Flat Stock .250" Thick, 6" X 6" Size
Cost: $45.44 each - STOCK
  • Connects entire dribbler assembly to the robot
4mm snap thrust bearing
Vendor: McMaster-Carr
Part No.: 7817K33
Description: Metric Nylon Snap-in Thrust Bearing for 4mm Shaft Dia, 1.45-2.34 mm Sheet Metal Thick
Cost: $1.32 each
  • supports dribbler shaft in the swing
3/8" Washer
Vendor: McMaster-Carr
Part No.: 93286A009
Description: Aluminum washer 3/8" OD,.175" ID, 1/32" thick
Cost: $3.52 for 100
  • Washer between the swing and hex standoff
Neoprene Rubber Tube
Vendor: McMaster-Carr
Part No.: 7505K86
Description: Ultra-Flex Neoprene Rubber Heat-Shrink Tubing 3/4" Expanded ID, 3/8" Shrunken ID,
Cost: $8.97
  • Roller and dribbler gear spin on dribbler shaft
  • Material is shared with the hinge shaft

Calculations

Torsion Spring
  • Analysis was done using the Work-Energy Principle with the assumption that the only work done is from the torsion spring and gravity. Because the dribbler assembly swings and has zero velocity at both positions, only the kinetic energy of the ball was used, at its maximum value of 10 m/s
Roller Speed
  • Gears were selected for a gear ratio lower than 2007. The 2008 ratio is 1.5. This was with the hope of having more torque available for the roller to grip the ball.
Dimensional Analysis
  • Using the Buckingham Pi theorem, an unknown function expressing the moment the dribbler roller puts on the ball based on other parameters was developed.
  • The inputs to this function can now guide the testing plan for the dribbler
  • The mom

Dribblerdimension.png

Notes

  • 4mm steel shaft chosen to increase strength to prevent bending of dribbler shaft when hit with a ball
  • roller diameter - .5"
  • dribbler shaft still slides free in between two snap-in thrust bearings and can be removed to allow the roller to be changed out
  • several 4mm holes were widened to .170" holes to allow easy assembly with the 8-32 threaded shaft
  • it proved very difficult to even squeeze 4mm shaft through the thrust bearings
  • due to unknown errors a few addtional washers were placed in the assembly
  • on the left arm a small cut was created to allow the motor shaft to protrude
  • a new motor plate was created and fits flush to the motor
  • it was found when the original motor plate was attached and fastended, it would add a high amount of friction and actually stalled the motor
  • a big issue is that the 2 dribbler arms must be connected around either the back or the front - and not rotate independently
  • this independent rotation swivels the motor around, putting more stress and wear on the gears, or makes the gears not even mesh
  • the small standoff closest to the motor was replaced with a hex standoff, as it would hit the motor gear slightly if the motor was pushed up a bit
  • a 4mm die will be purchased to thread the shafts, preventing boring of 4mm holes

Changes from Prototype

  • a standoff now near the roller itself to provide structural stability, connect the two formerly independent swing arms, and protect the motor from ball impacts
  • clinch nuts will be used to anchor the assembly to the robot, making it much easier to remove the dribbler assembly
  • the motor mount plate now connects to the hinge axis, the motor, and the front standoff
  • the 4mm hinge and roller shafts will be threaded to fit 4mm hex nuts
  • the gear ratio between the motor and roller has increased from 1:1.4 to 1:1.75
  • the dribbler roller diameter has increased from .5" to 5/8"


Dribbler bar prototypes

  • shaft diameter on ends of bar - 3mm
  • maximum diameter of dribbler - .75"
  • the dribbler bar prototypes will be lathed and done coated with neoprene heat shrink

Dribbler bar prototype drawing

dribbler bar prototypes

  • 3/4" diameter aluminum bar stock
    • $8.34
    • McMaster part number 6750K181
  • 3mm diameter aluminum bar stock
    • $6.94
    • McMaster part number 1681T21
  • 3/4" neoprene heat shrink
    • pack of 5 for $8.97
    • McMaster part number 7505K86
  • 3mm e-clips
    • pack of 100 for $3.03
    • McMaster part number 98543A101

2007 Dribbler

Drive gear

  • attached to the motor
  • SDP/SI A-1B-2MYK05045 Data sheet
  • 45 teeth, 3mm bore, 22.5mm pitch diameter

Dribbler gear

  • attached to the roller. This is done by pressing having a set screw in the gear interfere with the roller. Both the gear and roller are free to spin on the shaft, which permitting easy change.
  • SDP/SI A-1B-2MYKO5020H Data sheet
  • 20 teeth, 3mm bore, 10mm pitch diameter
  • gear ratio from motor to drilbber = 2.25

Motor

  • 15.9mm diameter, 3mm output shaft

Specs from CMU

  • Dribbler motor gear from SDP-SI: S10T05M042A0303 Module 0.5, 42 Teeth, 20° Pressure Angle , 2024 Aluminum alloy Gear
  • Dribbler bar gear from SDP-SI: S10T05M028A0305 Module 0.5, 28 Teeth, 20° Pressure Angle , 2024 Aluminum alloy Gear
  • spur gear reduction 1:1.5
  • Dribbler Motor - Maxon
  • nominal dribbler bar speed = 28200/5.4*1.5 = 7833 RPM. It is, of course, adjustable by software.
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