Tweet
I went to the pond today, and took the usual suspects; the yet to run prototypes and some of the tried and true with new modifications. I was about to back the truck out of the driveway and thought: Maybe I should take THAT one as well. After all, I put a new motor and propeller in it since it's earlier failures a year or two ago, why not?
What I'm talking about is a 10-year old scaled-down version of Jay Turner's "Pool Racer".
Why did I build one? It was cheap, simple to build, allegedly fast, and I had the parts on hand. It's nothing more than a couple of blocks of foam and a motor with a straight shaft. Pretty easy in my book.
That's where the problems started. Jay designed this back in the days of brushed car motors and NiCad batteries. Pretty beefy stuff. So a decade ago, I built a micro (now mini) version using the power systems we had developed for the mini hydros. This consisted of a 3000 Kv outrunner (26mm diameter), a 2S LiPo and an Octura X430. The problem was the power to weight ratio had changed considerably. I put it in the water, hit the throttle, and got an instant imitation of a Saturn V rocket launch. There was no horizontal movement, only vertical. Scared the cr@p out of me.
So over the years. I toyed with motors. Brushed motors, brushless motors, but I could never find a motor/prop combination to do it justice. Motor couplers were an issue too. Then a year or two ago, I found this motor: https://hobbyking.com/en_us/b20-30-3...or-3060kv.html. Cheap enough I thought, and about the same Kv as we were running on the other hydros, so I bought one. I had some problems mounting it, but nothing that couldn't be overcome. But what about a propeller? The small motor probably couldn't spin an X427 (the smallest decent propeller of the time). By then I had a better lathe, so I chucked up a driveshaft, stuck an aluminum X427 on it and turned it down to 24mm. While I was at it, I cut the tongues off as well. This gave me effectively an X624 prop.
So I stuck this thing in the water and it actually worked quite well. Jay's design has rather tall sides to accommodate the car motor it was designed around and I copied his proportions exactly. As a result, there's a lot of empty space in mine with proportionately large side and frontal areas. Going upwind it ran on just the step and the prop. Going downwind, it skipped and flew like a perfect throwing stone.
So now what?
I think I'll get some more blue foam and styrene sheet and build a more streamlined and low-profile "Pancake" hull and move the drive train from this one to a new one. It was fast (sort of), it was cheap (REALLY) and it was (almost) out of control (I did flip it once 
). A revised one will have a lower CG. 
What I'm talking about is a 10-year old scaled-down version of Jay Turner's "Pool Racer".
Why did I build one? It was cheap, simple to build, allegedly fast, and I had the parts on hand. It's nothing more than a couple of blocks of foam and a motor with a straight shaft. Pretty easy in my book.
That's where the problems started. Jay designed this back in the days of brushed car motors and NiCad batteries. Pretty beefy stuff. So a decade ago, I built a micro (now mini) version using the power systems we had developed for the mini hydros. This consisted of a 3000 Kv outrunner (26mm diameter), a 2S LiPo and an Octura X430. The problem was the power to weight ratio had changed considerably. I put it in the water, hit the throttle, and got an instant imitation of a Saturn V rocket launch. There was no horizontal movement, only vertical. Scared the cr@p out of me.
So over the years. I toyed with motors. Brushed motors, brushless motors, but I could never find a motor/prop combination to do it justice. Motor couplers were an issue too. Then a year or two ago, I found this motor: https://hobbyking.com/en_us/b20-30-3...or-3060kv.html. Cheap enough I thought, and about the same Kv as we were running on the other hydros, so I bought one. I had some problems mounting it, but nothing that couldn't be overcome. But what about a propeller? The small motor probably couldn't spin an X427 (the smallest decent propeller of the time). By then I had a better lathe, so I chucked up a driveshaft, stuck an aluminum X427 on it and turned it down to 24mm. While I was at it, I cut the tongues off as well. This gave me effectively an X624 prop.
So I stuck this thing in the water and it actually worked quite well. Jay's design has rather tall sides to accommodate the car motor it was designed around and I copied his proportions exactly. As a result, there's a lot of empty space in mine with proportionately large side and frontal areas. Going upwind it ran on just the step and the prop. Going downwind, it skipped and flew like a perfect throwing stone.
So now what?
I think I'll get some more blue foam and styrene sheet and build a more streamlined and low-profile "Pancake" hull and move the drive train from this one to a new one. It was fast (sort of), it was cheap (REALLY) and it was (almost) out of control (I did flip it once ). A revised one will have a lower CG.
The plan view is essentially the same except I rounded the nose enough to make it just under 350mm. The profile view resembles a Frisbee with a flat stern. I think I will make 3 templates from 1/4" MDF (the upper hull, the lower hull, and the hatch) and use my table-mounted router to cut the foam to shape. That way, I can make as many as I want. The rest is simple, some 1/32" styrene sheet, and I'll cut some motor mount parts from 1/16" ply in the "extra" space on a sheet from my rigger project.
I may leave the old hull/driveshaft/motor mount/servo/rudder intact for future experimentation, but it will definitely be relegated to the "Retired" pile.
It's maybe 20~25mph, but for it's diminutive size it's smoking! You could probably run it in a large fountain or a moderate-sized a swimming pool. It would probably get lost in an Olympic-sized pool. 
Comment