ROV Contest Questions!
(We get mail!)
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Using a Multimeter (volt meter or amp meter) |
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Why a battery? Why not use an AC/DC power supply or converter? Fred responds: Believe me, an AC/DC power supply would save my back! Our concern is safety. With all kinds of power supplies on the market, or in the garage, we can't ensure a safe shock free system. Even with a ground fault interrupter, when we work with water we are concerned about short circuits. We've gone one step further and use gel cells instead of the typical Lead Acid Car Battery. The gel cell doesn't spill and has other safety features. |
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Can you help me understand amps, volts and watts? Frank responds: Hey this is going to be fun! I drew two diagrams for you, first check out How Water Works, then look at How Electricity Works. |
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We are having trouble locating motors, we have tried the places on the site, but they do not seem to stock the motor you recommend. Please give us some direction. Fred responds: For this year's contest, the Monterey Bay Aquarium has a limited supply of motors available to contest participants at a low cost. 3 motors and 3 propellers are available for $15 (includes shipping). These motors operate under the 7amp specification for the contest. With all 3 propellers operating underwater it runs under 5 amps. This means that there is a possibility that someone may enter the contest with more powerful motors. We also recommend waterproofing the motors!I have a multimeter that has setting for measuring volts and amps, where do I set the test leads? Frank illustrates! Check these setups out: Voltmeter Amp Meter By the way, you can get a digital multimeter for about $20. |
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I use a 12 volt car battery to test my ROV at home in a pool. I am not using an amp meter to monitor any of this, what will happen to me in the contest? Fred responds: Careful, you may be in for a disappointment. Your car battery can put out hundreds of amps. I have an ROV with small motors that will use more than 10 amps at 12 volts. (Exactly how much I don't know, it is off the scale.) In the 2002 contest, we will be operating with a 7 amp fuse in line with the power source. This means if you come with motors that run higher than 7 amps underwater you will blow the fuse and be out of that event! |
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Will the fuse make my ROV perform poorly? Fred responds: The fuse will not change the performance of the ROV's. It will blow if your vehicle operates above 7amps! It is very important that you test your vehicle before the contest! |
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Two questions come to mind. 1) If the calculations of power are done, would hydraulics be allowed? 2) Does the battery exclusion for RC also require total power to be at or under 60W? Fred responds: More good questions! Thanks!Yes, hydraulics could be used. The hydraulic pumping device would need to be inline after the voltage regulator. So a DC device that pumps water, and plugs into our regulator would be limited to the total allotment of 7 amps. Please do not consider using oil in your system, the pool people will most likely reject it. I haven't heard of an RC working well under water unless it has a floating antennae. Fill me in if you know something else. The battery for the RC can only be for the transmitter and cannot supply power to the ROV, it would only provide an infrared, radio or acoustic signal. That signal may trigger a solenoid, but the power to the solenoid would come from the 7 amps. |
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One of the team coaches for our group, would like to know if they can use pneumatics system (air) using a tube connected to the tether from the control box to introduce air into the ROV during its operation. The air would be supplied using a syringe, blowing with your mouth or other means. The purpose of the request is to have the capability to change the ballast of the ROV during operation in order to replace or assist the vertical motor. It appears the rules intend that the ROV be operated exclusively with electric motors. Please clarify whether an external source of air may be used. Fred responds: I like the idea, I'd love to see the innovation but somehow we need to work within the power limitation of 7amp. Standardizing power is an attempt to find equal footing. The students are definitely not allowed to pull on the tether to control their ROV. Blowing into the tether, or using a syringe, or a tank of compressed air, requires energy that would need to be accounted for. Compressing gas requires energy. So to answer your question I'd say NO.I've seen a battery operated small aquarium type air pump, if it could be incorporated into your design so that it utilized energy included in your 7 amps allotment...I'd say it would be fair. Frank responds: Wow........I love the ideas that are springing up for this! You have a great job. I think your response is correct. The use of air power (pneumatics is transfer of energy) would need to be in the calculations of total energy use. Amps multiplied by volts equals watts and needs to be in the 7 amp window. Blowing into a tube (human energy input) is not much different (energy added to the system) than pulling on the tether to get the ROV do something. So blowing and/or pulling is out-(human energy input to the system). BUT the use of a pump and air is a really cool idea (the SubPro team is toying with exactly that for this years ROV) and just needs to be in the window of 7 amps. Pretty simple. FUNNY BONE note: Have you ever tried to blow down a tube to any depth????? It is not very practical and I have this image of a kid (contestant), cheeks splitting, red faced, huffing and puffing, .......... or a team of kids .......you get the picture........ |
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What do you mean by compressed air? Fred responds: We typically get compressed gases from pumps that condense their volume. The gasses are stored in pressurized tanks or canisters. Some people want to use compressed gas to power their ROV. Since it takes energy to compress gas, having a pressure tank supplement your ROV, or blowing into a line that goes to your ROV, takes energy that we've got to count. The only way we could see that every ROV has the same energy available, is to limit the power supply to 7amps. If someone has a small pump built into their control line, or on their ROV, they could be compressing gas using the power (7amps) available at the contest during their 8 minutes of competition.
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I understand the team is one adult and three youth. They will have their entrance to the aquarium paid. Can their family members come and pay entrance and watch the competition? Please let me know. Our first meeting is next Monday, January 29. We have secured our city pool, and to build excitement we are going to let the kids go play with the ROV we built at your class. I look forward to hearing from you. Thanks. Kim responds: I am so glad you guys are excited about this! The aquarium passes are just a perk. The competition is actually being held at the Monterey Peninsula College and spectators ARE welcome (though seating is limited.) For your day at the pool, I encourage you to build the obstacle course that the kids will be competing on. Its really simple and made out of PVC. The design is outlined in the design specs we sent you and are also available online. Let us know if you have any other questions. We will be emailing out the scoring sheet for the design category so your kids will know what we are looking for. |
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Are wooden propeller allowed in the competition? Can there be an onboard battery along with the outside power source? Kim responds: Yes, you can have a wooden prop but no onboard battery is allowed. |
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I put shrouds around my propellers and my ROV slowed way down, what's going on? Fred responds: What's going on is something I need to learn about also and that is hydrodynamics. The real techies that do this for a living believe the shroud offers protection to your hands, protection to the prop, and if designed right can enhance the performance of the ROV. The space around the propeller needs to be large enough, the inlet and outlet need to be large enough. You also have to watch that the outlet is not blowing against the frame. I've heard them talk about filing the edges of the shroud so it has hydrodynamic qualities. |
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I see all kinds of information about motors and props, do the control boxes make a difference? Fred responds: It is easy to lose electrical efficiency with poor switches, weak solder joints, or improperly sized wires. The tether and power cords need to be considered also for proper size.
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