Topics Regarding Power Sources

Overview

• Ok, here is the issue. This year there is a handicap on IC Engines. This poses a problem for us because that is the system we currently are running. We need a solution as soon as possible. This is meant to be a discussion on what type of Power system we should be running on whether that is Gas, Electric, or another alternative.

Electric Drive

• I have been looking around at electric motor systems. I found some motors here: http://www.robotmarketplace.com/products/LSM-M1120046.html that look awesome as far as power and efficiency goes. I feel that if we can come up with an electric drive system, it would be best for the following reasons.
  • We dont have any weight left to use for more cameras and other things (including the weight of the oxygen system that we would have to account for). Removal of the IC Engine would most likely significantly reduce weight. We would not have to start with a handicap of weight and cost of the oxygen system.
  • Control would be much easier than having to deal with throttle servos and braking could not only be done electrically, but we may even be able to use the energy from braking to back charge our batteries.
  • The electric current used to power the hydraulic solenoids, brake and throttle servos could be transferred directly to the motor control and motors that we would choose, making the electric efficiency look more appealing as far as energy storage goes.
  • Also, from a programming standpoint because we are already set on not using the propeller, the code will all have to be re-written anyway, and control of a fully independent skid steering is probably easier as well as gives us more mobility.

~Ryan

• Before we buy Lithium Polymer batteries, we should consider LiFePO4.
  • For $569 we could buy a 2lb 12V 6Ah LiFePO4 battery that can support a burst of 280A. But, if we just buy the cells, we can build our own battery with higher specs for even less than that. Building a 42Ah battery with individual cells would require 120 cells at $2.60 each. So we could make one for $312. I highly suggest using this technology over Lithium Polymer. https://s.p10.hostingprod.com/@www.voltphreaks.com/ssl/catalog/product_info.php?cPath=1_23&products_id=29

~Tyler

• Just to keep in mind, we need to figure out if $$$ is our limit or if weight is. Because lead acid is heavy but cheap, while Li-Ion/Li-Poly are lighter and expensive. -Ben

• Right, we will need to decide this because without and engine, full gas tank, and hydraulic pump with fluid we lose a lot of weight. If we can get the chassis quoted alone at Parallax Price, we can lose a lot of cost. We need to figure out which is the best option for us.
• We will also need a motor controller if we electric. This one looks to be excellent http://www.robotmarketplace.com/products/RTQ-AX2550HE.html for our application.

~Ryan

• Also one thing that we would need to consider if we go with the individual LiFeP04 cells is how we are going to connect them all together. As you usually can not solder to them. If they come with tabs spot welded on then this is not a problem, however judging by the image it looks like they do not.

~Jordan

• From what I can find, it looks like LiFeP04 batteries are lower energy density than Li-Ion/Li-Poly. Their main benefits are high power density (current source capacity), quick charge time, and improved safety over Li-Ion/Li-Poly. It seems like energy density is our first priority. Current source capacity could also be important, but we don't need 240A. (at least I hope we don't need 240A...)

~Joey

• I agree with Jordan that building our own battery could be difficult primarily because we would have to be able to insure safety and load balancing. There seem to be plenty of solutions that cost more but you can get 50Ah out of with proper load balancing. Personally, I would rather spend a thousand dollars on batteries than risk a couple hundred dollar failure on competition day. If someone has the experience and skill to build a properly balanced and stable battery system, than we may be able to do this, but if not, $750 isnt a bad price to pay for a stable system.
• If we want to sacrifice some weight for cash, we could go lead acid. I found these this afternoon http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3506. With something like this, we could easily buy two of them and have a spare on hand with a complete charge. This way, we could know for a fact that we would have all 40Ah at our disposal for the entire half hour of competition.

~Ryan