Well that was before VexU teams heard that beyond 8 motors will lower your motor torque
is that because the robot battery doesn’t offer enough current. In Vex U wouldn’t they be able to legally add a power expander by making modications?
Nope, as a VexU team member at worlds, our motors must interface directly with the brain. We can have an extra transmitter or robot battery for secondary electronics, but they cannot drive the motors.
It is also worth mentioning that V5 motors are hard to interface with, after fixing one motors, I couldn’t figure out how to communicate with it except by the V5 brain.
The V5 battery can produce up to 20A so each motor in normally limited to 2.5A. Whenever you have more than 8 motors plugged in (not just running), the firmware automatically limits each one to 20 / the number of motors plugged in amps, resulting in a lower maximum torque.
A power expander can be used for powering more motors. With Vex u a modification will be more likely.
Power expander is a Cortex accessory. There is no V5 version of it yet, unless I missed something . So the only motors you can use with power expanders are 393, which are prohibited in VEXU.
<VUR5> There is no restriction on the number of V5 Smart Motors that Robots may use. No other motors, servos, or actuators are permitted, including those sold by VEX (e.g. the 2-Wire 393 Motor).
Note: Pneumatic actuators are permitted within the guidelines of <VUR9>.
The problem with the power expander is that we can’t modify the brain nor the battery. Because of this, we are limited by Vex’s software current limits.
The 20A limit is not a limitation of battery chemistry as much as it is a safety to prevent overheating.
VEX would actually have to release a V5 power expander though, and I highly doubt that’s anywhere but near the bottom on their list of priorities, probably somewhere just above releasing the V5 SDK. What they could do is let the user set the current limits for each motor (up to 2.5A) at runtime such that the total sum of all the current limits doesn’t exceed 20A.
I guess Vex U team are better off with using the cortex in that case if it’s easier to modify and configure.
Also nope, VexU must use V5. There are days we wish we could go back, but V5 still works pretty well.
Aren’t you allowed to use any system you wish? With that what other exceptions are there from Vex Robotics competition?
Not according to the VEX U Game Manual appendix.
Maybe i was mistaken. Then what’s the difference between Vex U and VRC other than the age?
VexU has a few differences. For specifics, I encourage you to read Appendix E of the tower takeover rules.
The main talking points
- Two Robots: we form our own alliance, one robot starts in a 15" cube, the other in 24"
- Extra Electronics: we can use extra electronics that directly interface with an unmodified brain.
- Longer Auton : 45 sec auton, 1:15 driver control
- 3D printing and custom fabriation: We can 3D print and machine our own custom parts.
There are other differences not mentioned here, these are the ones that impact our team most.
Thanks for the information. Usually are Vex U teams comprised of University students?
Here is the section on drive team members:
<VUG6> Each Robot is allowed up to three (3) Drive Team Members, as stated in <G6>.
a. Drive Team Members MUST be post-secondary school individuals. Any matriculated individual
enrolled in post-secondary school is eligible to be a Drive Team Member.
b. Professionals not enrolled in post-secondary education are not eligible to be Drive Team
Members or participate on a VEX U Team.
c. Students that are dual-enrolled in both a secondary school and in post-secondary courses are
not eligible to be Drive Team Members or participate on a VEX U Team.
I thought it was ten motors before power was reduced. I guess I was mistaken.
After 8 it will start to lower power but it’s 10 before it’s really noticeable.
Cool, good to know. Thanks.
So in the future, VEX U teams may be able to use 20 motors without significant performance penalty if only a few are running at once.