Motor sizing

[Knufire]

Originally Posted by mreda

just a question what is the purpose of a motor controller? and the gearbox will allow the independent movement of the two motors or would I need two of them?

I'd definitely recommend that you call up Andymark. They have a phone number listed on this page here: http://www.andymark.com/Contact-Us-s/177.htm You should be able to speak to one of their engineers and they'll help you spec-out everything you need from their inventory for a one-stop shopping experience to finish up this project.

[mreda]

Originally Posted by asid61

You need two gearboxes. The motor controller lets you efficiently control speed of the motor without heat issues from the high current.
I highly recommend you find somebody who's already worked with FRC or robots in your area to help you; this would be an expensive mistake to make.

My best reference is someone who is young and doesnt really look at the dollar signs, this is just me getting another guide as well as to help me understand what I am doing rather than just taking advise and nodding blindly.

In terms of being able to handle the load though, would 775 pros motor and gearbox and SPARK motor controller theoretically work?

http://www.vexrobotics.com/217-4347.html
http://www.vexrobotics.com/vexpro/mo...reduction.html
http://www.revrobotics.com/product/spark/

thanks again guys

[asid61]

Originally Posted by mreda

My best reference is someone who is young and doesnt really look at the dollar signs, this is just me getting another guide as well as to help me understand what I am doing rather than just taking advise and nodding blindly.

In terms of being able to handle the load though, would 775 pros motor and gearbox and SPARK motor controller theoretically work?

http://www.vexrobotics.com/217-4347.html
http://www.vexrobotics.com/vexpro/mo...reduction.html
http://www.revrobotics.com/product/spark/

thanks again guys

Good to know you have somebody to work with, that makes me feel a bit better.
775pros could work, but because of their smaller mass you may face heating issues if you run this thing for a long time. CIMs are much safer and only cost slightly more (and have more reliable stock).

[Knufire]

Originally Posted by mreda

My best reference is someone who is young and doesnt really look at the dollar signs, this is just me getting another guide as well as to help me understand what I am doing rather than just taking advise and nodding blindly.

In terms of being able to handle the load though, would 775 pros motor and gearbox and SPARK motor controller theoretically work?

http://www.vexrobotics.com/217-4347.html
http://www.vexrobotics.com/vexpro/mo...reduction.html
http://www.revrobotics.com/product/spark/

thanks again guys

Strictly speaking, any motor can move any load. It's just a quesiton of how fast.

In terms of "handling the load", these are the factors you'll need to identify:

• How fast does the robot need to move?
• How much weight is it carrying (you already answered this)?
• A bit more about the geometry of the drivetrain (to estimate how much it's going to scrub/fight itself when it tries to turn)
• The material of the tread surface
• The surface it's driving on

The first question will identify the speed of your drivetrain, and the others help answer the question of how much torque you'll need the drivetrain to output. Multiply these together, and you get how much power you'll need in your drive; that'll allow you to pick an appropriate motor and gearbox for the drive.

[mreda]

So this instead?
http://www.andymark.com/Motor-p/am-0255.htm

[asid61]

Originally Posted by mreda

So this instead?
http://www.andymark.com/Motor-p/am-0255.htm

That's the one.

[mreda]

great thanks, Ill run it past my adviser. Another question completely unrelated, do any of you know of any either accurate gps or localization setups that I might be able to purchase or some nice tread setups/websites? Figured Id shoot it out there

[asid61]

Originally Posted by mreda

great thanks, Ill run it past my adviser. Another question completely unrelated, do any of you know of any either accurate gps or localization setups that I might be able to purchase or some nice tread setups/websites? Figured Id shoot it out there

Brecoflex has treads, Andymark started selling some treads this year (but they are rather expensive).
For GPS I don't know; are you looking for ICs, the kind you stick in cars, or breakout boards?

[mreda]

Originally Posted by asid61

Brecoflex has treads, Andymark started selling some treads this year (but they are rather expensive).
For GPS I don't know; are you looking for ICs, the kind you stick in cars, or breakout boards?

a chip for the robot so it knows where it is. I found a rather inexpensive one (https://www.adafruit.com/products/746) but it isnt very acurate

[asid61]

Originally Posted by mreda

a chip for the robot so it knows where it is. I found a rather inexpensive one (https://www.adafruit.com/products/746) but it isnt very acurate

You're not going to get much better than 3m, from what I've researched about it in the past. GPS isn't going to give you pinpoint accuracy.
May I ask what this is for?

[mreda]

Originally Posted by asid61

You're not going to get much better than 3m, from what I've researched about it in the past. GPS isn't going to give you pinpoint accuracy.
May I ask what this is for?

its a research project I just received a grant for at my college. I am trying to automate process through robotics. Its great in theory but now that i am coming to application it is getting hard again haha.

[EricH]

Originally Posted by asid61

Good to know you have somebody to work with, that makes me feel a bit better.
775pros could work, but because of their smaller mass you may face heating issues if you run this thing for a long time. CIMs are much safer and only cost slightly more (and have more reliable stock).

VEX did some tests on the 775s and published the results. Short version, under some of the test conditions they only got about 9 minutes of continuous operation (I want to say that was the max power test), after which they needed a new motor. EDIT: http://motors.vex.com/775pro--compare to http://motors.vex.com/cim-motor

Fan-cooled motors don't take stalling very well, which is where you run into a lot of the heating issues (drivetrains tend to stall a bit). CIMs... Can't say I've ever seen one of those smoke when used in an FRC-size robot's drivetrain.

[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.

Before you make any more design decisions, you really need to take a step back and decide your design requirements.

For example you mentioned tracks, do you need really need tracks or will wheels suffice.

How fast does this robot need to travel, what terrain does it need to cross, what range( battery capacity) does it need to have etc.

Another thing to consider is will the grant be large enough to be able to afford the necessary components, wheels represent a huge weight, complexity and cost saving over tracks

[pilleya]

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

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.