Weapon:
Our main weapon is a vertical spinner with plenty of inertia. It must be able to handle a serious blow while continuing to spin. When searching for a rotational inertia for our battle robot, we need to make sure the metal is hard and strong but not brittle as to break on impact. We have therefore decided to use half-inch steel for our spinner. We will want to use 1018 or 4130 steel as they are strong steels but not too expensive. We plan to do further research into this which composition of steel we will pick and have begun prototyping to find the best material. [2]
Steel isn’t the cheapest material on the market, even flat slates of half inch steel are both expensive, and expensive to ship. If we buy a square foot of steel it should be enough to make 2-3 spinners and a couple sets of wedges.
1/2inch thick 8″ x 8″ 1018 Steel sheet
Cost: $~95.64 [x2]
Attack Motor:
We will be using the same motor as our mobility motors, Propdrive v2 4248 650KV motors, which is a brushless motor. We want similar horsepower and similar power but a slightly higher max speed. This can be achieved by using a different gearbox ratio. This means we will be looking for a motor without a gearbox and instead will be attached to a gear and chain. The following motor has provides the proper voltage and torque that we are looking for in our robot and maintains a minimal weight.
Cost: $37 [x1]
Gears:
We see that gears and chain will be the best way to transmit power to the spinning mass. We believe this as this allows for gear ratio changes if we decide we want to, it allows for a cog to be implemented to reduce the danger of damage onto the motor directly, and also allows for less friction than direct gears. These can also be much more efficient and easier to install than belt drives or gears. [5]
We want a cast iron gear rather than a bronze gear as when looking up the tensile strength of cast iron, we found it was 40ksi rather than the tensile strength of bronze which is 18.1ksi.[6,7] When looking at the gear to purchase, we are looking about the 5 inch diameter gear. Unfortunately, these gears are quite expensive.
Cost: $~300 [x1] [approximation]
Chain:
We believe that a chain will be the best method to reliably and flexibly turn our vertical spinner. Due to its relative cheapness and our understanding that the chain will be a point of failure, we plan on purchasing several.
Cost: $12 [x2]
Armor:
Armor is a subject that has been talked about in many websites for many different battle bots in the community.[8] From these different sites, we have seen that armor is important, but can get very expensive very fast. Materials such as titanium, heavy steels, AerMet 100, and tool steel are all very expensive materials with strong qualities.[9] We hope to be able to use the machine shop steel for a large portion of the chassis and the defensive armor but we are unsure how much will be allotted for that or if we must purchase it. Overall, we suspect this could reach a value of upwards of an estimate of $200 considering we need steel sheets like this, but we also need metal corners, joints, and chassis parts. We are unsure what the machine shop has to offer. [10]
Cost: $~200 [approximation]
Total Attack Cost: ~$750
Sources:
[1] https://mechanicalc.com/reference/engineering-materials
[2] https://grabcad.com/tutorials/choosing-the-right-materials#:~:text=Steel%20alloys%20commonly%20used%20in,need%20to%20be%20well%2Dbalanced
[3] https://getmetals.com/steel/flat-bar/1018/cold-finished?1=2%22,3%22&gclid=CjwKCAjwzt6LBhBeEiwAbPGOgSmvWj-2kE729bp-yWrWK5Bm4uIjaq07J2M8z-XLGceggGJ_r2w_HxoCTREQAvD_BwE
[4] https://www.robotmarketplace.com/products/0-e30-400-12.html
[5] https://www.powertransmission.com/blog/a-look-at-belt-chain-and-gear-drive-technology/
[6] http://www.matweb.com/search/DataSheet.aspx?MatGUID=ec56a89f37f74e2f867a64b0f87f1e9d&ckck=1
[7] https://www.azom.com/article.aspx?ArticleID=6294
[8] 1.MET2019_Giese_Justin.pdf, https://www.instructables.com/Phoenix-30-lb-Combat-Robot/, and https://www.stem.org.uk/system/files/elibrary-resources/2019/07/How%20to%20build%20a%20combat%20robot%20V1.2.pdf
[9] https://grabcad.com/tutorials/choosing-the-right-materials and 1.MET2019_Giese_Justin.pdf)
[10] https://www.onlinemetals.com/en/buy/carbon-steel/0-0239-carbon-steel-sheet-a1008-cold-roll/pid/12781?variant=12781_24_24&gclid=CjwKCAjwzt6LBhBeEiwAbPGOgdNxmQ-9OyJ_c94e3WBLN3XvhUzLmF1jF0zEiCnjFj4_86RXhBJgNRoCmJ0QAvD_BwE