Robo Power

1. Robo Power Mary Silliman Age:11 Wake County Oakrabots 4-H Club

2. Purpose • To describe challenges in working with a LEGO robot • To compare different ways to power small robots and find which ones work best • To describe where robot power systems will take us in the future

3. Robots are important to us… • In manufacturing, robots are used to make everything from cars to computer boards; • In agriculture, robots feed livestock or fertilize and harvest crops; • In medicine, the best surgeons are now… ROBOTS! (no slips); nanotechnology will some day send medicines through blood vessels directly to an infection or tumor.

4. Robots became important to me because… • As a member of a 4-H Club/First LEGO League team, I noticed… • RoBetty, our robot did not complete missions she was programmed to run OR • Robot completed missions but was too slow to finish in the time allowed • So I asked myself, “Why did this happen?”

5. To solve this problem, I examined each robot system and asked,“What could create such a slowdown?” • Here is an X-Ray of RoBetty (poster) • The Body or chassis of a robot is the “skeleton” that holds parts together • Faulty parts or added weight might slow things down, but even with the same weight we had slowdowns

6. So I looked at the Mobility system—wheels, tracks, or slides—the robot’s ”feet” • Parts that get stuck, loose, dirty, worn, or slick can slow a robot but RoBetty’s wheels were A-OK • Looking at the Tool systems—attachments like a bar, scoop, crane—”hands” that help a robot do a special job, I checked for • stuck or loose parts…but none were a problem

7. The next system I looked over was • The Sensors—tools that detect light, sound, movement, or touch objects—the ”nerves and sense organs” of the robot • Stuck, loose, broken, or misplaced sensors can slow a robot and • Poor room lighting or shadows can confuse it and make it work slower But RoBetty’s sensors were all in the right place

8. One robot system I suspected was… • The Controller or microprocessor—the “brains in the brick” • If circuits in the “brain” are not receiving enough electricity, they may not make decisions or communicate completely with the motors that drive the wheels • I learned to read the brick’s “face” (screen) to see if the right program was loaded • Sometimes it was as simple as watching the robot perform the way it was programmed

9. One final check of the Controller is always to look over the computer program that tells it what to do— • “Do the settings for time, distance, wheel rotations, or power level get RoBetty where I want her to go?” • (Think hard) “Have I changed the program since the last time RoBetty ran the course correctly?” If the answer is, “No,” then to Power we must go…

10. The Power system is both the “stomach”—or energy supply—in the form of DC batteries, and the “heart”--or delivery system, including motors and wires • Depleted batteries may not supply enough charge to match the programmed distance (like the Energizer Bunny running down)---whether the program is based on time, distance, or rotations • No two motors are exactly alike--wear takes its toll—so they may not transfer power equally So what could we do about power?

11. Most motors are not that different, so I decided to focus on batteries. Four different solutions I tried were.. • Testing batteries • Putting in new batteries • Trying different kinds of batteries • Trying something besides batteries

12. Testing Batteries • The simplist test is very practical—if a toy works well, the batteries are OK; when it goes slow, one or more batteries is weak (replace all old batteries at the same time) • A thermochromatic battery tester like those on some battery packages change color in response to heat from a “live” battery—no color: battery dead

13. Testing Batteries • A Volt Meter (demo) is another inexpensive tool to check how much energy is left in a battery • And, of course, our robot has its own Battery Level indicator (demo)—that indicates how much power is available from the batteries

14. My second power solution was just to • Put in new batteries. This can become an expensive and complicated habit. • Alkaline batteries stay at peak power for only a short time, so a robot always needs a new one…not to mention keeping track of which are new and used; • New-technology batteries like NiCd and NiMH sometimes require “conditioning” or a process of discharging and re-charging before they work at peak…not a quick-and-easy solution.

15. My third solution was to try different kinds of batteries and use the most reliable kind. • Alkaline (demo) are the cheapest and most common but they run out fast and only recharge a few times. Most are not built for the high-drain demands of small robots or computers. (“Sorry, Charlie.”)

16. Another choice is the • Nickel-Cadmium rechargeable. NiCads are more expensive than alkalines but still pretty affordable, especially when you consider that they can be recharged (in 1-2 hrs.) up to 1500 times. They produce the strongest current and can handle high-drain electronics. However, replacing them means losing program memory and tossing them is a problem since Cadmium is toxic.

17. Nickel-Metal Hydride: costs more than alkaline but is still affordable since it recharges in 1-2 hrs. up to 1000 times; works better for high-drain devices like small robots; There are no memory effects upon replacement and no toxic chemicals…if they ever wear out enough to toss.

18. My final battery choice was the • Lithium-ion. It is light, but the most expensive. It can be recharged many times and is non-toxic, but can overheat; used in laptop computers and cell phones; high power output, zero memory effects

19. In my research I found out about many issues behind the solutions • Voltage—How much a battery can give • NXT requires 7-8 volts • AA Alkalines are 1.5 volts x 6 = 9 volts • NiCad, NiMH, Li-ion are 1.2 volts x 6 = 7.2 volts • Volt--electrical force that powers a current • Current—the flowing rate of an electrical charge (electrons) in a conductor • Amphere—the amount of charge that passes a given point in a second (for batteries: milliAmps)

20. The issues behind the solutions • Battery Capacity —amount of energy stored in a battery Current AMP x HRS of Current (2 amp/hr x 2 hr = 4 amps) • NXT requires 7-8 volts • AA Alkalines 1700 mAh (but only at peak) • NiCad, NiMH, Li-ion are 1700-2400 mAhs (for several hours at high drain) (ex: bottle mouth)

21. The issues behind the solutions • Discharge —How quickly a battery gives out • NXT requires 7-8 volts • AA Alkalines = 1700mAmp (runs at 1.5 V short time, soon to 1.0 V, especially in high-drain devices) • AA NiCad, NiMH, Li-ion = 1700/1800 mAmp (1.2 V continuously; even in high-drain devices)—use an “A” rated charger • AA NiMH can discharge even without use

22. The issues behind the solutions • Re-charging—Exactly how much power can a battery give after it is re-charged? • AA Alkalines (Energizer) begin at 1700 mAmps but don’t re-charge to that capacity • NiCad, NiMH retain capacity, esp. if conditioned (fully discharge, then re-charge)

23. Other Power Sources Industrial Robots powered by • Pneumatic • Hydraulic • Fuel Cell • Electrical • Efficient • Little Maintenance • Quieter ->May Create Compressed air for Pneumatic ->May Create Power to move oil in Hydraulic

24. Future Power Sources New technologies are being developed for the robots of the future • Solar • Fuel Cells • Bacteria

25. Conclusionsfor Powering Robots of the Present • Use batteries with greater capacity and consistency (NiCd, NiMH, Li-ion) • Check battery meter on robot • Charge/change batteries often • Start practice or competition with new ones • Keep a good supply of charged batteries • Take care of batteries (no dropping) • Check robot systems for other problems

26. Sources • 4-H Robotics Probe curriculum • All Battery: www.all-battery.com • Energizer-How Batteries Work: www.energizer.com • Greenbatteries www.greenbatteries/com • How Batteries Work: www.howstuffworks.com • Logic Battery: http://logicbattery.com • Society of Robots: www.societyofrobots.com