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Simple Robot Electrical Design

Simple Robot Electrical Design. Presented by: Al Skierkiewicz, Broadcast Engineer, Mentor Team #111 Rookie Year 1996. Outline. Ten things a Rookie Team needs to know. Real world design example. Minimize the losses. What happens with a motor under varying conditions.

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Simple Robot Electrical Design

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  1. Simple Robot Electrical Design Presented by: Al Skierkiewicz, Broadcast Engineer, Mentor Team #111 Rookie Year 1996 2007 FIRST Robotics Conference

  2. Outline • Ten things a Rookie Team needs to know. • Real world design example. • Minimize the losses. • What happens with a motor under varying conditions. • Working with a design and layout. • Techniques and layout. • Tools • Questions 2007 FIRST Robotics Conference

  3. Top Ten Things Rookies Need to Know. 2007 FIRST Robotics Conference

  4. 10. The Robot Section of the manual and the Tips And Guidelines Docs are not the only place to get info. • Check the FIRST website (www.usfirst.org) often, team updates come out weekly and the Q&A allows teams to ask questions and get answers from the GDC. • The FIRST website (FRC Documents) also will have manufacturer specification sheets and the Tips and Guidelines will also include manufacturer website info. • Check team websites for suggestions and up to date info on KOP motors • IFI, Innovation First, has a great website and PDF documents for all it’s products. 2007 FIRST Robotics Conference

  5. 9. The main battery is a high current device. • The main battery is capable of 600 amps for a short period of time. • This is enough current to burn wires, motors, dangling bracelets, rings, and necklaces. • This is enough current to weld most metals including the terminals on the battery. • In a two minute match, it is more than capable of running a robot with a six motor drive. 2007 FIRST Robotics Conference

  6. 8. You shouldn’t control two motors with the same speed controller. • I don’t recommend this practice. Rules in the past have allowed certain motors to be controlled by the same controller. • Most motors already exceed the current specs for speed controllers. • Motors rarely need the same drive signal. • Doing so will result in less than designed operation. 2007 FIRST Robotics Conference

  7. 7. A stalled motor is one that is not moving. • A motor is stalled when no power is applied. • A motor is stalled when mechanically prevented from turning. • A motor is stalled (near stall) when used in a tank style drive design without using omni wheels. i.e. the motors will draw max current in every turn. • A stalled motor draws maximum current, 130 amps for small Chalupa (CIM) and 96 amps for the large. Six motor drives can draw over 500 amps! 2007 FIRST Robotics Conference

  8. 6. Snap action breakers do not trip at the rated current. • All breakers can function with up to 600% over current for a few seconds. • All breakers can function with up to 200% over current for almost ten seconds. • All breakers can function with about 150% over current indefinitely (based on internal temperature of breaker) • Breaker specs are available on FIRST Website • Breakers will “buzz” when repeatedly tripped. 2007 FIRST Robotics Conference

  9. Breaker Trip Curves 2007 FIRST Robotics Conference

  10. 5. Motors run at different speeds in opposite directions. • Motor brush bias causes this difference. • CIM (or Chalupa motors) have the least difference. • Similar motors on different sides of the robot will likely run in opposite directions due to mounting. • Speed controllers will supply the correct input power, when calibrated, for each direction. • The bias can be overcome in software or by driver practice. 2007 FIRST Robotics Conference

  11. 4. Mechanical design does affect electrical design. • Operating characteristics are influenced by mechanical design. Arms draw max current when parallel with the floor, long wires reduce power to critical motors. • Placement of components may lead to changes in electrical layout and wire runs. • Do not place speed controllers in a debris field from exposed mechanical systems (chain sprockets, open transmissions, pulleys bearings). • Replacement is a critical design factor. 2007 FIRST Robotics Conference

  12. 3. Wire does make a difference! • At the currents encountered, real world voltage drops of several volts can occur in your wiring. • All wire has loss, smaller diameter wire has greater loss. I recommend #10 for all CIM (large and small), the compressor and all Fisher Price motors. • Please remember both the positive and negative leads carry the same current. • Design for short wire runs. Loss is length dependent. • You can attach motor leads directly to speed controllers and/or cut them shorter. 2007 FIRST Robotics Conference

  13. 2. If you use the default software, you must calibrate the speed controllers. • Speed controllers and joysticks are not matched. • Joysticks are not precision devices. • Calibration will match joystick travel and center position to speed controller operation. • Without calibration you may not be able to achieve maximum output from your motors. • Without calibration, motors may not zero speed or brake when the joystick is released. 2007 FIRST Robotics Conference

  14. You are never alone! • As a rookie, you should have access to a mentor team in your area. They are your greatest asset. • Team websites like www.chiefdelphi.com can have a lot of useful information. Beware that some answers might not be accurate. • FIRST Q&A is a valuable resource, check it often. • I can be reached at askierkiewicz@wttw.com one person per team please. • At events, any team can help. Your lead inspector is a valuable resource. 2007 FIRST Robotics Conference

  15. Real world design of an arm motor. • Lets take a large Chalupa motor with the following specifications: • Stall Current = 96 amps • Peak Power Output = 280 watts • Choose operating point of 1600 RPM@225 oz-in., 40 amps, 160 watts out. • If input= 12v@40amps, then • R motor =12/40=.3 ohms 2007 FIRST Robotics Conference

  16. Large Chalupa Motor Curves 2007 FIRST Robotics Conference

  17. Stall RPM=0 I=96 Amps Chosen operating point 40 amps, 160 W 1600 RPM 2007 FIRST Robotics Conference

  18. If there is resistance in series with a circuit, the current will decrease in direct proportion to the resistance. A decrease in current will provide less power from the motor. Ohm’s Law R (motor)=V/I=12V/40A=0.3 Ohms Calculating for 4’ of #10, 2’ of #6, 0.011 ohms for the battery internal resistance and .002 ohms for breakers and terminals. .3+.008+.0028+.011+.002=0.3238 ohms I (motor) =V/R=12V/.3238 Ohms=37 Amps 2007 FIRST Robotics Conference

  19. Motor Load Point with Real World Losses New Point for wiring. 20 watts less power 40 oz-in less torque 2007 FIRST Robotics Conference

  20. If this is an average system and four small Chalupa drive motors are near stall, I (stall) =100 amps x 4 motors=400 amps. The battery is capable of delivering more than 600 amps when fully charged but has an internal resistance of 0.011 ohms. So for this example 400 amps flows through 4’ of #6, a few connectors and the fuse panel, then the voltage loss in this robot is: V=I*R=400*0.0238ohms=9.52 volts. That leaves only 2.5 volts available for all other systems including the RC. In terms of motor current, I=V/R=2.5/.3238 ohms=7.7 Amps (if the RC were still in control). 2007 FIRST Robotics Conference

  21. High current on drive motors New point Only 20 watts output 60 oz-in. of torque 2007 FIRST Robotics Conference

  22. Each intermittent load on a motor reduces the available current and therefore reduces power and RPM temporarily. • This is why many robots with arms are not able to raise a game piece as designed, other motors are causing losses in the system. • It is also why a team that raises the arm when not moving may not achieve the same movement while driving. 2007 FIRST Robotics Conference

  23. To Begin Design and Layout of Robot Electrical System, know your robot system. • It is essential to know the list of requirements for the system before you begin. • It is essential to have an grasp on the location of mechanical parts and needed clearance. • Must work with mechanical designer to place major components in a central location, i.e. battery, main breaker, terminal block and fuse panels. 2007 FIRST Robotics Conference

  24. You must know how many motors will be used. • How many and what type of motors for drive and where located. • How many motors for actuators, are they required to be speed controlled or operated by relay. • How many motors for steering. • How many servo motors. • Where will all these be located on the robot? 2007 FIRST Robotics Conference

  25. You must know what electrical hardware you will be using. • How many Victors and how many Spikes will be needed? • Will you be using the SLU or crimp connectors for the mains wiring? • How do I attach cable to the battery terminals? • Do I need to use insulated or non insulated terminals? • Do we need to solder? 2007 FIRST Robotics Conference

  26. Know the installation failure modes of all devices. • How should it react when powered? • Does it have indicators and what do they mean? • Know the correct handling of all devices. • Check wiring polarity for all devices before applying power! • What are the mechanical stresses due to mounting and termination? • What happens if you drop the device? • What is the correct wiring polarity? • How should it be electrically protected? • Is there a common mistake when installing? 2007 FIRST Robotics Conference

  27. Now, Let’s Begin With a Plan! • Make a table of controlled components needed • Add control components (Victor or Spike) • Obtain the control inputs and outputs from the software team • What Breakers are needed? • Will sensors be associated with the motors? • Other data, color coding 2007 FIRST Robotics Conference

  28. Color code everything, make a list of functions. Electrical and software will need this list. 2007 FIRST Robotics Conference

  29. Color code everything, make a list of functions. Electrical and software will need this list. Motor List 2007 FIRST Robotics Conference

  30. PWM & Brake Current and Polarity 2007 FIRST Robotics Conference

  31. Electrical Design Begins • Select a position for the Main Battery and compressor if you are using pneumatics. (The battery and compressor are heavy so they can be used to balance the robot.) • Select a position for the main breaker and the terminal block near the main battery. • Select a position for the Maxi Block and ATA Fuse panels near to the terminal block. • Select positions for the Speed Controllers (Victors) and relays (Spikes). 2007 FIRST Robotics Conference

  32. Electrical Design Begins • Select a position for the Robot Controller and the Radio Modem. • The RC does not need to be near the outside of the robot but should be easy to see without removing covers. • The modem should be placed so that the antenna can be placed away from metal objects. Do not bury in the robot frame. • Use a 9 pin extension for the programming port and tether port if RC is inside the robot. 2007 FIRST Robotics Conference

  33. Electrical Design Begins • The main breaker needs a solid mount and the case is easily cracked. • Mount the main breaker where it is easy to access but not positioned so that another robot could easily bump the “OFF” button. • It helps to label the main breaker location so your robot can be turned off if needed. • The terminals need to be insulated! 2007 FIRST Robotics Conference

  34. Electrical Design Begins • Mount controllers near the motors they will control. • When mounting speed controllers, position so that it is easy to see the indicators. • Allow some open area so that cooling air may flow around the controller and through the fan. • Make sure you can access the calibration switch. • Controllers can be mounted in any position but should be secure. • Don’t place near mechanical parts that will produce metal flakes. 2007 FIRST Robotics Conference

  35. Primary Electrical Wiring • Consists of #6 wiring, 50 amp Anderson connector, Main breaker, terminal blocks and wiring to breaker panel(s). • Carries all robot current. • The same current that flows through the red wire flows through the black wire. • The main breaker is a temperature sensitive device. • #6 wire is about .0005 ohm/ft. At 200 amps, at least 0.4 volt drop across the KOP supplied wire length, more if the Anderson connector is damaged. 2007 FIRST Robotics Conference

  36. Bad #6 AWG Wiring Long wire runs, shared currents with high current loads. Voltage to RC estimated to be below 9 volts during pushing, much less during stall. High Current Returns All robot current flows through these wires. To RC 2007 FIRST Robotics Conference

  37. Better #6 AWG wiringCurrent sharing is reduced, wire runs are shorter. Jumper still taking a lot of current. RC fed at sensitive position on block. Voltage to RC estimated to be max 9.6 volts during pushing, less during stall. Drive current only flows Through these wires. To RC 2007 FIRST Robotics Conference

  38. Best #6 AWG wiring Current sharing is reduced, wire runs are shorter. Jumper carries less current, reduction in single point failure. RC fed from minimum loss terminal on small breaker panel. Voltage to RC estimated to be at least 9.8 volts during pushing, less during stall. To RC 2007 FIRST Robotics Conference

  39. Many team batteries are wired this way. Terminals close to battery edge run the risk of abrasive breakdown of insulation. Unequal wire length makes connection difficult and mating questionable. 2007 FIRST Robotics Conference

  40. Best battery wiring. Terminals are turned to inside and are mounted on inside of terminal, allowing battery case to shield them from abrasion. Wire length is equal to allow ease of connection. If battery or mount moves during match, secure Anderson connector with ty-wrap to prevent opening. Terminals (SLA or KPA4C) may be bent to reduce overall height above battery case. 2007 FIRST Robotics Conference

  41. Note battery terminals turned to inside, away from chassis supports. Terminals are well insulated and wires are held out of the way. Battery is securely mounted and cannot move. 2007 FIRST Robotics Conference

  42. Note: Wire is stripped back the length of the terminal, about ¾”. Insert wire between the shell and the terminal. Do not insert wire under screw! The screw pushes on the copper not the wire. When terminated properly, the wire should take on the shape of the shell and cannot be moved. You can solder but insert solder from the terminal side, not the wire side. Stop when solder flows to the insulation. This will keep the wire flexible. For SLA or KPA4C Connector Termination Soldering is Recommended! Insulation is a must! 2007 FIRST Robotics Conference

  43. Crimp terminals are also allowed. They are easily crimped with the corners of a vise if the correct crimper is not available. Solder these the same way as SLA or KPA4C connectors. There is a solder hole in the terminal side of the connector. Again only add enough solder to prevent it from flowing under the insulation. Pulling the wire should not give any movement. Insulate with electrical tape or heat shrink (A #10 push on shown for reference.) 2007 FIRST Robotics Conference

  44. Various hand tools: Ratchet style crimpers on left, then small wire strippers and cutters, followed by a cutter meant for #6 only. 2007 FIRST Robotics Conference

  45. Common Tools For Electrical Install 2007 FIRST Robotics Conference

  46. Automatic stripper shown with common T type stripper for 16-24 AWG. 2007 FIRST Robotics Conference

  47. Thomas and Betts crimper on left can be used for both insulated and non-insulated terminals. Ratchet crimper on right will not release the jaws until the correct force has been applied. The T&B crimper should be used on non-insulated terminals by orienting the slit in the terminal against the concave side of the jaw. When correctly terminated, the slit should remain closed and the wire can not move within the terminal. 2007 FIRST Robotics Conference

  48. Fluke 77 VOM • Useful for measuring all electrical on robot. • Measures voltage & resistance. • Use for troubleshooting. • Fluke 410 Current Clamp • Useful for measuring currents up to several hundred amps. • May give inaccurate readings when measuring output of Victor at less than full power but is still useful. 2007 FIRST Robotics Conference

  49. 3M Color Wheel contains a few yards of each of the EIA colors (resistor code). Useful for marking all electrical wiring and components. (power wires, Victors, breakers, Spikes, motors, and PWM wiring) 2007 FIRST Robotics Conference

  50. ¼” uninsulated Terminals Anderson Power Products Bent Terminal Flag Terminals 2007 FIRST Robotics Conference

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