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 ● P E - P M = Heat ○ When motor is stalled for too long, ○ heat burns the motor Effjciency % = P M / P E * 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 ○ #teeth input / #teeth output ■ Diametral Pitch (DP) ○ Essentially size of teeth - in FRC, 20 or 32 ■ Center to Center Distance ○ (D driving + D driven ) / 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 Small Space Needed Large Space Needed Average Space Needed #25 Chain 20dp Gear 3mm Belt Polycord VersaPlanetary 32dp Gear #35 Chain 5mm Belt

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

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

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

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

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

1403 Design Calculator-Belt ● Belt Options: ○ 2mm ○ 3mm ○ 5mm ● Belt ○ Pulley tooth count ○ Center Distance How to use: ○ Belt Size 1. Use the belt calculator to find the belt size 2. Then use the center distance calculator for exact ○ Ratio 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 How to use: ○ VexPro Part 1. Select Diametral Pitch of the gears you want to use 2. Select the driving and driven gears Numbers 3. Check VexPro for availability of products

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

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