I am new to VEX, and am really excited to be learning what VEX can do. And please forgive me if I am posting in the wrong part of the forum. (I wonder if there needs to be one for running NON-VEX parts and NON VEX competitions?)
I have a group looking to use a VEX Cortex for an Underwater Robot. It will be tethered to the cortex and battery, which will be safely waterproofed and protected on the pool deck.
Our question is this: Can we run Brushless motors off of a Cortex controller? We want to run hobby sized brushless motors, the kind you fine on RC cars, boats, and such.
I assume we would need some sort of speed controller, something like:
We will most likely be looking at other vendors, and ebay, as well, but I just wanted to get a link (which I cannot seem to get the link function to work correctly) to show you the size and scale we were thinking of.
If the speed controller has an RC pwm type input (which the one you linked does) then yes, you could use the cortex to control it (disconnect the red wire on the receiver cable though). You will need an external battery, don’t try and use the cortex battery to run these high current motors. The particular motor you linked isn’t compatible with that speed controller.
In terms of compatibility, make sure the ESC can provide enough current for the motor. For the parts you linked, the ESC has a max continuous current of 10A, the motor probably needs 2 or 3 times that under normal loads and its stall current is 10x.
I have never worked on underwater robots, however, motor size will depend on the mass you are trying to propel and how fast you want it to move.
You would want around a 100 amp ESC for a motor of that size. Like this one here http://www.hobbyking.com/hobbyking/store/__24565__HobbyKing_100A_ESC_4A_UBEC.html
Generally speaking you don’t have to get a higher rated ESC for your max amperage draw (which is 115) so a 100 amp esc should allow you to run your motor at around ~75% throttle comfortably. Like jpearman said, you would want to get a lipo battery to power that individual motor.
Great question about why we want to use a VEX Cortex. Two basic answers, really.
One, we already have them for classroom use, so they are “Free” for this project, we can just take one off of a clawbot, and hook it up, when we are done, we just put it back. There no cost in using it, and there is no point in leaving it in a cabinet if it is not being used, we have a couple back ups that we can use.
Two, we had tried using Arduino Uno’s in the past, with limited success. We still need to use motor controllers with them, and we found them to be glitchy when we ever had 2-3 motors running at a time.
Also, as a bonus, the VEX joystick just seems to be well designed, and is really easy to use. Not only is it ergonomically well designed, it just sync’s easily with the cortex, and is very reliable. We have had more hit and miss results with a joystick set up with arduino micro controllers.
(we do currently have a Talon motor controller running a large 12 volt motor off of an uno for another project, and it has been perfectly reliable. But that is just one motor, not 4 of them like we are hoping for with this project.)