Mechanical Power & Power Transmissions Overview of Presentation - - PowerPoint PPT Presentation

Mechanical Power & Power Transmissions

Overview of Presentation

• Power Transmission

○ Motors ○ Types of power transmission: ■ Gears ■ Chain ■ Belt ■ VersaPlanetary ○ Design Considerations

• Design Calculator

Motors

• Most common motors:

○ Falcon 500 - New brushless Motor/Motor controller combo ○ NEO & NEO 550- Smaller, lighter brushless variant of CIM motors ○ CIMS - heavy, but can be stalled for long periods of time ○ MiniCIM - ⅔ the power of CIMS, but more effjcient. Similar free speed, so can be interchanged ○ 775Pro - same power as CIM, but significantly lighter. Burns up almost immediately at max volt.

• Too many motors drawing current at one

time will brown out robot

Motor Basics

• Input: Electrical Power

○ Volts * Amps = Watts

• Output: Mechanical Power

○ Speed * Torque = Watts ○ Free speed is when torque = 0 ○ Stalled is when speed = 0

• Energy Loss: Heat

○ PE - PM = Heat ○ When motor is stalled for too long, heat burns the motor

• Effjciency % = PM / PE * 100
• Motors.vex.com for more info

Motor Considerations

• The number of motors used on

your robot during the match.

• The torque and power
• Brushless vs Brushed motors
• Position of the motors and

motor controller

• Is the motor protected
• Number of 40 amp breakers
• The Battery is not changing
• Charge of the Battery

Power Transmission

Typical FRC Power Transmission Methods

• 20DP Gears
• 32DP Gears
• 3mm Belt
• 5mm Belt
• #25 Chain
• #35 Chain
• Polycord
• Planetary Gearboxes

Gears

• Terminology

○ Driving and Driven gears ○ Gear Ratio ■ #teethinput / #teethoutput ○ Diametral Pitch (DP) ■ Essentially size of teeth - in FRC, 20 or 32 ○ Center to Center Distance ■ (Ddriving + Ddriven) / 2 + .003” ○ Pitch Diameter (D) ■ Imaginary circle where teeth actually contact ■ #teeth / DP ○ Outer Diameter ■ (#teeth + 2) / DP

Gears

Important Considerations:

• Rotation is reversed between

driver and driven shaft

• C-C accuracy is critical
• The larger the reduction, the

more forces in the smaller gear

• The higher in the chain the gear

is, the less forces

• Each reduction loses effjciency
• Gear-Shaft slop - backlash

makes control harder ○ Use hex where possible

• Must keep lubricated

Chain

Components of a Chain System

• Sprocket

○ Hub Type ○ Plate Type

• Chain

○ In FRC, #25 (.25” pitch) or #35 (.375” pitch)

Chain

Important Considerations

• Chains will skip if not tight

○ If using a precise c-c, testing is often necessary for accuracy ○ A tensioner (i.e. cam and slot) is a quick solution, but takes space and design time

• Avoid using “master links” or “half

links” - creates a point of failure

• Alignment of sprockets

Belting

• Types

○ GT2 3mm ■ Curvinlinear profile, provides better contact and indexing ○ HTD 5mm ■ Stronger, better for high load applications

• Center 2 Center is Critical with

timing belts

VersaPlanetary

• Pros:

○ Very high reduction in a tight space ○ Easy to assemble - highly modular ○ Come in 3:1, 4:1, 5:1, 7:1, 9:1, and 10:1 reductions (up to 100:1 ratio) ○ Add-ons for more designs ○ No complex design!

• Cons:

○ Not very strong, use small gears ○ High reduction means a lot of inertia

• VersaPlanetary Load Rating

Selecting A Transmission Type

• Considerations:

○ Reduction ○ Adjustable Distance ○ Strength ○ Effjciency ○ Directionality

Reductions

Large Space Needed Small Space Needed Polycord #35 Chain 20dp Gear 5mm Belt 3mm Belt 32dp Gear #25 Chain VersaPlanetary Average Space Needed

Adjustable Center Distance

No - have to mesh Yes- Requires New Belt Polycord #35 Chain 20dp Gear 5mm Belt 3mm Belt 32dp Gear #25 Chain VersaPlanetary Yes- Can make new chain length

Strength (High Torque)

Low Strength High Strength Polycord #35 Chain 20dp Gear 5mm Belt 3mm Belt 32dp Gear #25 Chain VersaPlanetary Average Strength

Effjciency

Low Effjciency High Effjciency Polycord #35 Chain 20dp Gear 5mm Belt 3mm Belt 32dp Gear #25 Chain VersaPlanetary Average Effjciency

Reverses Direction

Yes No Polycord #35 Chain 20dp Gear 5mm Belt 3mm Belt 32dp Gear #25 Chain VersaPlanetary Either

Design Calculators

• Make it easy to do the calculations for gear reductions

○ Different options for different applications ■ Drivebase gearbox ■ Lifting mechanism ■ Rotating mechanism

• JVN Calculator
• 1403 Design Calculator

○ Reduction calculator, has options for all types of belts, chains, and gears, with part numbers to quickly reference

1403 Design Calculator

• Gearing Options:

○ Chain ○ Belt ○ Spur Gear

• Displays:

○ Types ○ Center Distance ○ COTS parts/part numbers ○ Reduction

1403 Design Calculator- Chain

• Chain Options:

○ #25 Pitch ○ #35 Pitch

• Displays:

○ Input Distance ○ Sprocket Size ○ COTS parts/part numbers ○ # of links ○ Warning for tensioner

How to use: 1. Use the number of links calculator to find the center to center distance (keep the # of links even) 2. Use the distance calculator for exact center to center distance. 3. Check supplier for availability of products

1403 Design Calculator-Belt

• Belt Options:

○ 2mm ○ 3mm ○ 5mm

• Belt

○ Pulley tooth count ○ Center Distance ○ Belt Size ○ Ratio

How to use: 1. Use the belt calculator to find the belt size 2. Then use the center distance calculator for exact center to center distance. 3. Check supplier for availability of products

1403 Design Calculator-Gears

• Gear Options:

○ 20 DP ○ 32 DP

• Gears

○ Gear tooth count ○ Center Distance ○ Ratio ○ VexPro Part Numbers

How to use: 1. Select Diametral Pitch of the gears you want to use 2. Select the driving and driven gears 3. Check VexPro for availability of products

Resources/ Thanks

FRC Team 1678 Citrus Circuits JVN Design Calculator VexPro Rev Robotics Chief Delphi

What is the Compass Alliance

The Compass Alliance was founded in the fall of 2017 by FRC 3132 and 9 teams from around the world. The mission of the founding teams was to make a big impact on the FRC Community and its members. After months of research and hard work, The Compass Alliance was born.

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