Warlocks 8/5/05 TMU FIRST Robotics 101 u Week 1) Gears, Pulleys, Sprockets, Bearings u Week 2) Motors & Controls u Week 3) Pneumatics u Week 4) Materials & Fasteners u Week 5) Drivetrain and Framing Options u Week 6) Arm & Winch Options u Week 7) Team Building

Warlocks 8/5/05 TMU Long Arm is Hard u It take more effort to lift the Arm with the longer the Arm is. Torque= Force X Radius=> T=F X R Ugh!!! R=Radius F = Force T=Torque

Warlocks 8/5/05 TMU Short Arm is Easier u Shorter arms are easier Torque= Force X Radius=> T=F X R Not Bad! R=Radius F = Force T=Torque

Warlocks 8/5/05 TMU Long Arm with Weight is Impossible u Adding a weight makes it difficult to nearly impossible. Torque= Force X Radius=> T=F X R Errr…I can not move it! R=Radius F = Force T=Torque 100 lbs

Warlocks 8/5/05 TMU Add a Magical Gearbox u With a Magical Gearbox and a Geek turning faster, the arm moves. Torque= Force X Radius=> T=F X R It moves!! R=Radius F = Force T=Torque 100 lbs Magical Gearbox Magical Gearbox turns speed into Torque!!!!!!!

Warlocks 8/5/05 TMU Torque Calculation u Tetra weighted about 6 pounds u The Arm Length is about 4 feet u Mistake Number 1: You did not include the weight of the arm. u Weight of arm is 10 lbs evenly distributed (assumption), therefore add the following torque u Mistake Number 2: You use the stall torque of the motor. (I really thought you wanted the arm to move??? The stall torque means the arm won’t move. Use the maximum power torque or ½ the stall torque so the arm will move…..I think the idea here is that the arm moves.) Torque= Force X Radius = 6 lbs X 4 feet = 24 ft-lb Torque= Force X Radius = 10 lbs X 2 feet = 20 ft-lb Total= 44 ft-lbs Van Door Motor Torque= 35 N-m/2 *.737= 12.8 ft-lbs

Warlocks 8/5/05 TMU Torque Calculation Con’t u This means that the gear ratio needs to be at least 3.41:1 which is 44 ft-lbs /12.89 = u From experience, there are usually losses in friction/efficiency and your weights are off and you probably want a little more speed so a 6:1 or 8:1 works well. u Also, motors get worse after significant use or when they get hot and so a 3.41:1 may work at first but over time it may not do the job. u A margin here of 2X is the way to go. I recommend 8:1. It will always work then. u Backdriving motors can lose position. Back drive torque is the amount of torque you can put on a motor before the motor turns with no electrical power applied. The more gearing reduction in speed, the less backdrive.

Warlocks 8/5/05 TMU Winch Design u A Winch is basically and arm that is really short in length u A Winch is use to pull and wrap a rope, chain, wire. Winch Mechanism

Warlocks 8/5/05 TMU You Can’t Push a Rope u Remember you cannot push a rope, you can only pull rope. Winch Mechanism

Warlocks 8/5/05 TMU Winch u Winches can be used to lift/lower an object 100 lbs T=F X R =14ft-lbs X 12in/ft/1.5in = 112lbs (This Might just move the weight.) = 14ft-lb X 12in/ft/.8in = 210 lbs (This will move the weight at.8 X PI X 100RPM X 1min/60sec = 4 inches per second or 1 foot in 3 seconds) Using the globe motor.

Warlocks 8/5/05 TMU Scissors u What is a Scissors? For very little distance in the X direction, a great distance in the Y direction can be achieved. 2.8X.4x change X = 2.8x change Y (7 times) Example Only!

Warlocks 8/5/05 TMU Force of Scissors Force  = Angle of Scissors Force= 1/ [sine  ]* Force along Scissors T= F X R = Force X 4*Length Force = (1/ (sin (20 deg))*10 lbs Torque= 29 lb X 4 X 1 ft = ft-lbs Length= 1ft Force along Scissors Force