https://vexforum.com/attachment.php?attachmentid=6427&d=1341809892
This graph pretty much sums it up.
Additional info: usually the PTC would trip in a few seconds if the current is above 4 amp. Plan accordingly.
A couple of things to add.
Free current is specced at 0.37A, my measurements when I made the graphs showed it was much less, I used 0.2A but it can be less than that.
There is no hard current limit for the motor, without the PTC the motor would just draw close to stall current and overheat (I hear it takes about 5 minutes before the motor destroys itself from a reliable VEX source). PTCs are very non linear devices and the tolerances can be quite large, some trip much sooner than others (anecdotal and experimental evidence). The data sheet has the hold current at 0.9A and the trip current at 1.8A, how long and when the PTC trips will depend on many things and we can not put a definitive number on it. I use 1.5A as the sweet spot which corresponds to keeping the motor running at 70rpm or greater, however, even that is not guaranteed with something like a flywheel shooter where you know that even to get to that 70rpm point takes a lot longer than other applications.
Sorry, the graph is confusing. If you are at 1.5 amps, how are you at 70rpms? Wouldn’t you be somewhere around 40 rpms?
When you are using the blue line to find current, you read the current from the scale on the right side. But then for that particular value of current on the blue line, you must look to the purplish line to read at what speed your motor would be running given that current. You read the speed off of the purplish line by looking to the scale on the left.
For example, let’s say you want to know your motor speed when the motor is consuming 0.8 amps. You first would find the 0.8 amps on the scale at the right, run your eyes to the left until you encounter the blue line, then run your eyes straight up to the purplish line, which is the speed curve. From that point on the purplish line, run your eyes to the left to read the speed. From the blue line or the purplish line, you can also run your eyes straight down to read what torque the motor will be able to output at that number.
Or let’s say you want your motor to output 3 in-lbs of torque. You start at the bottom scale and find 3. Then run your eyes straight up until you hit the blue line. Then run your eyes to the right to read the Current scale, which would tell you that your motor would need about 1.2 amps when outputting 3 in-lbs of torque. If you wanted to know the speed at which your motor would be running when outputting that torque, you would go back to where you see 3 in-lbs of torque on the bottom scale, then run your eyes straight up to the purplish line. Then you run your eyes to the left to read the motor speed off the speed scale on the left.
thanks full metal. I am ready to give up. I am on the forum and the vex curriculum website every night and I still don’t know anything lol. i appreciate the info.
Don’t give up. The speed torque graphs can be confusing even when you understand what they are trying to convey. The table of values included in the original post is a little easier to understand.
https://vexforum.com/showpost.php?p=310291&postcount=2
Also don’t get too distracted by all of the technical data, start building, only research why some things don’t work as you expected as they crop up.
I agree. Don’t feel lost if you’re trying to understand some of the conversations now taking place on the forum. About the only people on here this time of year are hard-core Vex obsessives and maniac mentors. To just get started, you really don’t need to understand all the minutiae being debated about flywheel physics, ball spin aerodynamics and so forth. Some of the people discussing that sort of thing are college kids and old mentors who are trying to remember what they learned in school decades ago. 
Present and accounted for.