I had recently done maintenance on the Polaris, and when replacing the wheels had put the back wheel on upside down. The axle is off center on the mounting block, so upside down means the back wheel is a little farther away from the idler wheel than it should be. The effect is that the wheel touches the idler wheel, and looks fine, but when in the water and under pressure it loses contact with the idler wheel, so you don't get power from the back wheel. I found this by putting marks on each of the wheels to count rotations while the Polaris was moving around the pool. It was then easy to see that the back wheel was slipping.
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I had recently done maintenance on the Polaris, and when replacing the wheels had put the back wheel on upside down. The axle is off center on the mounting block, so upside down means the back wheel is a little farther away from the idler wheel than it should be. The effect is that the wheel touches the idler wheel, and looks fine, but when in the water and under pressure it loses contact with the idler wheel, so you don't get power from the back wheel. I found this by putting marks on each of the wheels to count rotations while the Polaris was moving around the pool. It was then easy to see that the back wheel was slipping.