Quote:
Originally Posted by roboruler
I’m going to be honest here. You are asking a lot of questions and it really seems like your knowledge in robotics is lacking. I am somewhat surprised that you received a grant from your college for a robotics research project without knowing that you need to use gearbox on a motor to increase the torque and reduce the speed and you don’t even know what a motor controller is
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Hi Mreda,
I’ll echo what Roboruler said, it doesn’t seem like you have a lot of robotics knowledge, but this is a great way to learn and you will indeed learn a lot through this project, you need to be really careful to not make any purchases before you have actually identified what you need and have considered all your options, It wouldn’t be good to end up with components that don’t work together or parts that are in-sufficient for what you require
I’ve had a look at your different posts, made some assumptions, identified your design requirements and have tried to offer a bit of advice.
Capable of carrying a 150lb load
Capable of travelling over varying terrains, you mentioned that you are looking at tracks and that you are thinking of 3D printing tracks. First of all 3D printed tracks will not work for this project as they will wear/break quickly under continuous operation. I would suggest that you don’t go down the path of tracks, although you may think that tracks are necessary for crossing over varying terrains, a robot with wheels especially pneumatic wheels will work better in most circumstances. A wheeled robot, will be more reliable, lighter, more efficient, cheaper to maintain and much cheaper to build.
Capable of travelling at a reasonable speed (let’s say between 5-10fps where 5fps is a person’s average walking pace).
You asked about accurate GPS modules that can be fitted to a robot, I take this to mean that you need the robot to autonomously travel a reasonable distance. This is important when considering power requirements for this length of operation. (Let’s say that you need this to be able to drive/operate for at least an hour between recharging)
You will need a very substantial amount of stored battery power to run a robot of this size and weight for an hour, especially if you are driving for a lot of that time, so probably large marine SLA batteries
You said that the robot needs to be 18 inches in diameter, that is very small for a robot that you want to do this much, it is unlikely that you will have enough room for everything in this size, without making the robot tall which means a high-centre of gravity which makes it easier for the robot to tip over. A larger robot will be much more capable of going over different terrains, and a rectangular or square robot will be much easier to build than a round robot.
Let’s say that your robot base weighs 120 pounds (with batteries), that’s 270 pounds with the payload. I believe that you are quickly moving into a class of robot that certain FRC parts will be unsuitable for. This is not for an FRC competition so you are not limited by FRC grade/legal motors. You might be better off searching further afield for parts I would have a look at:
http://www.robotmarketplace.com/store.html
They sell parts for the larger/ more rugged robot that as I see it you are planning to build.
I would also suggest that you have a look at the JVN calculator:
http://www.chiefdelphi.com/media/papers/3188 it is a good resource that will help you determine what motors and gear-ratios you will need to accomplish your task.
In regards to the motors, The only FRC motor capable of doing the job would be the CIM, and if you choose to use wheels between 8 and 10inches in diameter and get around 10fps speed you’ll need about a 20:1 gear-reduction with at least 2 CIM’s on each side or at least 4 in total, and that will be with a very high current draw from the motors especially if you plan on driving up slopes with the robot. I would suggest taking a look at some of the larger motors available from the robot marketplace, especially those with built in gearboxes.
You mentioned that cost is important for this project, none of the parts that you are going to need to build this robot are going to be cheap you’ll need to plan well and make some tough decisions, such as potentially reducing some of the functionality/requirements for the robot. Cutting corners on cost in robotics of this scale doesn't usually end well and you'll end up with a lower quality and less reliable final product in the long run.
Lastly I wish you good luck with this project, it sounds really awesome and it is great that your college has given you the support to do this. If you have any questions about anything I have said, or about robotics in general PM me.