In this design criteria lesson, we're going to carry on with part three of our component selection. After completing this lesson, you'll be able to apply calculations to select components and make informed design decisions. In this lesson we're going to be focusing on the amount of thrust provided by our motor and how our battery choices are going to affect both the lift as well as the flight time. So the DYS motor that we're talking about here is the MR2205-2750KV. We already know that the 22 is the diameter of the stator, the 05 is the height of the stator, and the 2750 or constant velocity is multiplied by the voltage to give us the max RPM unloaded. But what does all this mean? Well, DYS provides these thrust charts with their motors so we can reference the motor, how our battery choices are going to affect things like the thrust as well as which propellers that we want to choose. The first thing that we need to consider is the mass. Now I've picked out a couple different batteries that we're going to talk about. The smallest three cell battery that we're going to talk about gives us roughly a total mass of 814 grams. The largest four cell that we're going to talk about gives us a total mass of roughly 1130 grams. So at this stage, we're not too concerned with the amperage or the amount of current that the battery can push out. We're solely going to focus on the three cell and four cell differences and how they apply to the thrust. So first, let's take a look at the example at 50% input with a five by four and a half prop on a three-cell system. So the three-cell or 11.1 volt system will provide 371 grams of force. Now, this is times four because we have a quadcopter in Ford Motors. So the total is going to be 1484. We need 814 grams bare minimum to be able to get off the ground. And we have 1484. This is not quite the two to one ration that I'm looking for, but it is enough for us to get up in the air and fly. Now when we talk about our thrust ratio or the amount of force that we provide as opposed to the amount of weight that we need to lift, I like to shoot for two to one at 50% throttle in this design case. This is going to give us plenty to fly, and enough room that if we go up to 100% throttle, we're going to have great maneuverability and we can get somewhere fast. But let's take a look at some other numbers. For the same prop on the same motor, but a four-cell system or 14.8 volts, we now have 561 grams of force. Multiply that by 4, we get 2244 or 2,244. Now we have to lift 1,130. We're pretty close to that 2:1 ratio. We're at about 1.95, so this is pretty good. The input at 14.8 volts is giving us a lot more output even though we have to lift more mass we can still account for it and get a better thrust ratio. But now let's take a look at what it means to do a three cell with a six inch prop as supposed to a five. So at 50% we're now getting 481 grams of force. So this is 1924, once we multiply it all out, and we're still only lifting 814 grams. So this gives us the best thrust ratio. But we have to be careful when we talk about this, because instead of needing eight amps of current on 50% on the five inch prop, we now need 12 amps of current. So if we factor in the amount of current needed for both of these set ups, at 11.1 volts 50% on a five inch prop we need eight amps. However, at 11.1 volts on a 6-inch prop, we need 12 amps. So we're actually drawing quite a bit more current. So even though we're lifting more and we're not really increasing the mass, we're not going to have nearly the same amount of flight time. So let's take into account the rest of the equation. We now want to look at the battery and how that's going to affect things. So we want to take a look at the difference in mass. We want to take a look at a difference in the voltage and the current. So the three batteries that we're talking about here are all Turnigy. The first one is two 1500 milliamps wired together. The second one is two 2200 milliamps wired together. And the third one is a four-cell system with 2,650 milliamp hours wired together. By wiring two batteries together, we're able to double the current but keep the same voltage. So this is a nice way for us to increase our capacity, increase our flight time, and be able to add a bit more mass to the system to get that roughly 50 to 66%, mass being part of our batteries. So as we look at this, our smaller three-cell system is 214 grams for 2 batteries. Our larger four-cell system is 530 grams. And right in the middle, we have 4.4 amp hours in a three-cell system at 376 grams. Now remember, all three cell systems are going to be about 11.1 volts. The four-cell system however is 14.8. As we look at these three cases, we want to take a close look at not only the difference in the mass but how the voltage is going to change the overall equation. So the next column we're looking at is going to be the five by four and a half or the size of our prop. I omitted the six by four and half prop because we're really planning for a five inch prop here. And the reason we're doing that is because we want to be able to configure the battery. Now there was no six by four and a half prop shown on a 14.8 volt setup. Now that's because the 14.8 volt is not going to be spinning that six inch prop. Ideally, DOIS wants you to run a five inch prop on that system. Because the five inch prop was available for both the three cell and the four cell, I want to make sure that I stick to something that allows me the flexibility to run the four cell batteries or run the three cell batteries. So now you're wondering where did these numbers come from, 14 amps, 20 amps, and 18 and a half. Well, if we reference the thrust chart, we can take a look at each of these numbers. First, we have to lift 800 grams. So if we divide that by 4, each motor needs to be at least 200 grams of force. Now I do want to note that we're taking the bare minimum total mass and we're using that as our thrust. We're going to need more thrust for us to actually get off the ground and fly, but this is a great way for us to baseline everything and take a look at the raw numbers. So in order for each motor to be able to lift 200 grams, on a 5 by four and a half prop on a three-cell 11.1 volt system, we fall between the 25 and 50% input. We're pretty close to 25% because that gives us a 175 grams while the 5 by 4.5 prop on 50% setup gives us 371. So I estimated this said about three and a half amp input to get us 14 amps only multiplied by all four motors. Yeah, as we look at this, our battery is only providing 12 amps and you might be wondering how I arrived at that number. Well, remember the amp hour value is how much amperage it's going to supply for one hour. With our battery, if we take 3 amps for 1 hour, we can provide roughly 6 amps for half an hour or 12 amps for 15 minutes. And again, to simplify all the numbers, I'm taking 15 minutes of what these batteries can supply. And I'm taking a look at how that compares to the amperage input we need just for the bare minimum. Now remember when we talked about our design criteria, I wanted at least 15 minutes of flight time. So the 15 minute supply on the battery will help us understand how it's going to work. If we take a look at the larger capacity three cell system instead of three amps we now have 4.4 amps. But we have to lift 975 grams. If we divide that by 4 we have to have 244 grams of lift for each motor. Now, again, that falls between the 25 and 50% but it's quite a bit farther away from the 25%. So I estimated about 5 amps, or 20 amps raw form motors. Now, the larger capacity battery, of course, gives us more amperage, but it only supplies 17.6 amps for 15 minutes. We need 20 amps. We're only getting 17.6. We're still not quite there for 17 minutes of flight time. If we take a look at the four cell system, we have to lift quite a bit more. Each motor has to be able to provide 282 grams of force. Now on a four cell system, we are now at 14.8 volts, the same prop. And we're right about 25% input. Now this is great because we have 280g for each motor, and we're only pulling 4.66 amps of current. If we take a look at this, the battery is going to provide 21.2 amps because it's got a larger amperage. So 21.2 amps for 15 minutes, we only need 18 and a half to fly. This is going to give us enough average to be able to fly for 15 minutes. Now, the way that we can address this entire problem is we can take a look at the total mass, we can take a look at the battery setup, and how that's going to affect our flight time. With less mass, we need less amperage to fly for the same amount of time. Because we're talking about the amount of thrust we need and how much throttle input that's going to be, the four cell system looks like it's going to give us the best bang for the buck. It can run at 25%, it can give us enough thrust to gt off the ground and we still have 50, 75, and 100% throttle to get quite a good thrust ratio out of this. At 280 grams, that is a one to one thrust ratio at 25% throttle. When we go to 50, we have 561 per motor, 75 we've got 908, and as we go down the list at a 100% throttle each motor is providing 965 grams of thrust. Now that means that one motor can almost provide enough thrust to get off the ground, this is giving us a roughly four to one thrust ratio. This is going to let us be really maneuverable in the air, get to where we need to fast, then we can reduce the amount of throttle and hover, and just keep the throttle at the lower, roughly 25%, and survey certain areas. So, overall when you start to design something like this, whether it's a quad-copter, anything, you want to take a look at this type of data. You want to compare your options. You want to figure out what the best routes going to be. Now, I've actually built this set up on the three amp hour system on a three cell battery. And I can tell you that from my experience I was able to fly for about eight to ten minutes on this set up. Some maneuvers but mostly hovering. So these calculations for 15 minutes supply at 12 amps requiring about 14 amps, it's pretty realistic. It gives us a good idea of where we need to be. So this tells me that if we decide to go with a four cell system, with the larger capacity batteries, we're going to be able to fly for probably 20 minutes on that set up. So at this point we've given you a lot of information on how to pick components to develop a quad copter. Now, as we move forward, we're going to be starting our build by using the DYS motors we've talked about. We're going to start with the smaller capacity batteries, the three amp power two battery setup which is lightest setup that we have. And we're going to take a look at how it translates to our real world flight time. Being able to keep the same propellers, to keep the same motors, and simply upgrade the batteries to larger capacity for cell systems is going to give us quite a bit more flight time. So we know that we have that option to increase the batteries as long as we design it so that the batteries are centered on our components, and we center all the mass on those batteries. Now, again, we're looking at roughly 50 to 66% of our mass coming directly from the batteries. So they will have the grace effect on the balance of our components. As we move forward in our course, it's important to remember all these values, remember where they came from and how they apply to what we're doing. Even on the courses laid out, so we use all the same components that we're talking about. It's perfectly acceptable for you to take a look at these and figure out better components to use. Whether it's a different motor, whether you're planning for a different battery system, or simply sourcing different components so that they're lighter or easier to manufacture, or put into our design. I will give out a full parts list. And with this course I've also supplied an Excel spreadsheet that has all of this information on it as well. So you can take a look at that, the components that we're using, and how that correlates to what we're doing here in this course.
