What do you mean bottomed out? Do you mean you have to pull the lever all the way to the handlebar? There is only two solutions for that with a mechanical disc brake: the cable needs to be tightened, or the pads need to be closer. Tightening the cable will bring the pads closer, but it is possible the caliper and pads need to be reset. One of the drawbacks to a mechanical disc paired with a hub motor is that it is much more difficult to adjust the inner "fixed" pad. Most require a hex wrench; you often have to remove the caliper to access the adjuster.