You don't even need weights to develop quads. Sissy squats are a great exercise you can do anywhere, just lower your knees in front of you near to the ground and push back up, you feel the burn. The operating lever of your quads (lower leg tib & fib) need to be perpendicular with the direction of resistence to fully engage the muscle. Traditional squats only activate quads about 25% which is why you can pile so much weight on ... there's no leverage, but increased risk of injury