If we had the electrical diagram we could do it ourselves.
Now by logic, if what you need is energy, it would be bypassing it.
According to the scheme of a micro usb is like this:
and a usb type A would be like this:
(for a usb 3 look in google go out all the schematics of the pinhole)
following the two connectors of the images, what I would do would be to take two type A usb, one male and one female, and join them with clable and solder.
then fuck mobile charger that is 5v and one of them would join the positive and negative, which is seen in pins 1 and 4.
With that, he would have the energy he needs.
the safest thing is this so connected inside that cable.
You can also buy the female male cable and cast it and then splice the red and black wires that are the energy to join them in the cable that is already done, you just have to cut the cable to join in the same colors.
I see that the Max2 looks identically on the outside to max letter, could I do the same in my model? I read in this forum that in my model the onyx had disabled the possibility of otg.
I do not know if it is necessary to introduce some code before to enable it, I have the doubt, however if someone wants to prove I think that what I say can work, if it is true that the only thing you need is extra energy.
Maybe one day try if I have time, for the bluetooth keyboard, with the program that I say goes well, also you do not need to be anchored to any clable, if it is true that it would be fine to put a usb memory.