Motor speed does not increase to 127

Using the On-Line Window, when we run our motors they increase speed but stop increasing at around <-85 to 85>. When running the motors for our scissors lift arms, the motors stop running when less than -85 and greater than 85. Please help with any insight.

Thank you.

You are probably tripping the over-current protector by overloading the motors.
Since higher motor speed values =>higher PWM duty cycle => higher current.
Cortex ports 1-5 combined are on one 5A limit, also 5A for ports 6-10 combined.
To get further suggestions, report the number and type of motors, and what motor ports they are plugged into.

For the scissors lift, two of the motors are in ports 3 and 4 and the other two are in ports 7 and 8. All motors are 393.

You have a load on the system which is your scissor lift from going faster. An unloaded motor goes at ~100 rpm.

This is an old but really good post describing what is happening with the motors.

https://vexforum.com/t/motor-torque-speed-curves-rev2/21868/1

“At the 4 in-lbs the 393 needs 1.44A, is about 33% efficient and runs at 73 rpm”

So you must have somewhere under 3 in-lbs of load moving your scissor (I am guessing 2.25 - 2.4 in lbs from the graphs and data in here).

Reducing the load on your scissor and cubes will make it run faster. (e.g. more rubber bands, reducing friction points, less metal overall, etc).

We did plug in a motor with no load and the motor speed stopped increasing around the +/-85 range. I would think the ~ 0-100 rpm range would, at no load, be across the 0-127 and -127 to 0 range fairly linearly. Am I wrong in this thinking?

Yes it should be going up to 100 rpm but it is not linear. i would order another motor and toss the bad one. :frowning:

(one question: are your batteries charged? You may not be getting enough current to the motor. Could it be a bad 2-3 controller?)

This thread was using the speed gears, not the torque ones, but the phenomenon is the same. The speed you get is not linear to the PWM signal you put in. (value -127 to +127 PWM into motor[value] is not linear to the rpm on the other end)

https://vexforum.com/t/24cs-motor-control-value-remapping/23959/1

You can see that on an unloaded motor the max speed is reached well below 127. There is some sample code in the thread too as a bonus!

You can use your values out and make your own mapping!