Reefvan,
I had made a similar one of these a couple years ago....It will still run well but long term it did have some problems.
With too small a motor it has a hard time turning the whole arm evenly,with decent seals it becomes "sticky" so it turns in short quik bursts if you know what i mean.
The other problems i had with it, were after the seals wore in abit it water slowly leaked through them.
It isnt bad in itself as the water just drips back into the tank, it just ended up being a big algal mess with intense lighting on that area.
Another problem is the mounting of the motor and armature to the peice,(mine was mounted to the underside of my canopy) if where the armature is connected to the pvc is not exactly inline with the base (where it pivots on) the whole thing turns unevenly...this was hard on the motor too, i finally was able to correct it but if i paid myself a wage for doing so, i could have bought the real thing several times over
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Finally, No seal will be truly a seal if turning.....thus flow is always limited to prevent leakage, I was able to run a mag 2 but with some small leaks...so that was the units limit.