SAWs boat Brakes?

[NativePaul]

Thanks Tyler, that airboat solution looks impressive but with the amount of water going up in the air it must be trying to stuff the tail pretty hard, not a problem when you have a flat bottom that wide, but if you just have a prop for support or a couple of skis at the most I can't imaging it not upsetting the boat.

Wow, Chris's boat looks awesome that really does give me some things to think about. I was thinking of the flaps hinged directly off the rear boom and being full width but maybe being smaller you can run them at a much higher AoA for the same downforce and get more airbraking effect, I may be able to do the same thing full width by running them at an angle of attack where they are stalled, but that would mean running them through a position where they are providing more downforce than I want as they move before they stall.

Looking at the front ride pads is interesting too, is that suspension, or just a screw ram to make the AoA easily adjustable? My dad thought about trying suspension like that on a race boat back in the 90s, but as far as I know he never took it off the drawing board.

I have considered a glider type spoiler on the tub, and discounted it as I didn't think it would add enough drag, but for some reason I had not considered a high aspect ratio jet type airbrake, that could work well.


Thanks Jay, I had thought of that, and it would be dead easy for me to implement as I use air ESCs that have a brake function that I can turn on, and I use wires so no worries about the flex unravelling. I have never tried it though for fear of it lifting the back and stuffing the boat though, if it doesn't have that effect, or the effect isn't too big I will try it out.


Christian, I have certainly never even thought of a disc rudder, that is well outside of the box, I guess you mean something like a pizza wheel on bearings with just the bottom in the water, it would spin with the water flow and effectively decrease the speed of the water flowing across it?


I have pondered the need for a water rudder at all. I will have at least 1 vertical stabiliser and putting a rudder on that/those would be fairly trivial. With contra-rotating twins I shouldn't have prop walk to deal with, so an air rudder may be enough to steer it down the course, not enough to get it turned round at the ends, but if I was to extend it down to strut height it would be out of the water when planing, and be in the water when at displacement speeds. Does anyone have any input on this idea?

No worries Tony, I would like more details but just knowing it has been done before is very helpful, do you recall if he took his boat back in a trash bag or if it went home in one piece?

[properchopper]

Paul,

Again, I don't recall. He did have some issues but I don't remember what they were - it was 14 years ago. He's a forum member - try PM'ing him.

Here's an early attempt at dealing with the slowing down issue :

I've recently tested a new technique to stop; the Speed Pond Lateral Acceleration Terminator [ SPLAT ] and it works as described

http://www.youtube.com/watch?v=TzcSxfHyFfo

[Ch.Lucas]

Hi Paul,
yes , your are a thinker , no need of tons of drawings and pics. Yes the pizzacuter is the way. I made small disce and looked for the same cornering force and messured the trust with an open flow water stream. The result is clear. If not only a bearing is mounted it can also be driven by a small motor so the ruder generate some trust.

Happy Amps Christian

[eXoNerated]

Hi Paul,

The MGM and APD have synchronous rectification. They both have very elaborate brake functionality as a result .The 120 amp F3 controller might work for you if you want to try the inverters brake like Jay suggested.

Happy Harmonics
Hubert

[Bushmen77]

Why can’t you program the controller to go into reverse . Not much is needed just so you have maybe 10% . Your not going to actually go in reverse but I think that Input will try to slow Down the motor that will slow the prop and break it.

[fweasel]

Why can’t you program the controller to go into reverse . Not much is needed just so you have maybe 10% . Your not going to actually go in reverse but I think that Input will try to slow Down the motor that will slow the prop and break it.

Not a good idea to spin a flex cable in the wrong direction

[properchopper]

Food for thought.....

https://www.youtube.com/watch?v=DjALseBuBTY

[Bushmen77]

Your not really spinning it backwards . You just using a little power to slow it down .
Example when we started to run electric slot cars . If you with wide open you were going too fast to corner. So my dad rigged up a battery on the controler . When the controler lever was at nutral it would apply a little power to go backwards. So I have to hold the lever part on to get the car to stay in one spot. When I raced I would come down the stright away wide open. The other guys tried to keep up. But just before I hit the turn I would release the lever and it would put the breaks on fast. It just slowed the car down. When we race the newer rc cars we can program it to break by doing the same thing to the motor. We use the motor to break. We have rc boats now that have revers built in doing the same thing. But I never went full throttle and hit reverse to try it. Maybe you have to adjust the amount of power in reverse till you get a controled slow done. I don’t see how it would not work once dialed in plus it’s just a radio setting . Get someone with a boat that has reverse and do a test and try it. I am will but can’t do it till summer. But the way it works your not spinning the shaft backwards just slowing it down faster.

[RaceMechaniX]

Using the prop to brake or worse reverse results in a very bad condition where the tail lifts and nose stuffs. At high speeds this is catastrophic.
This happened to Joerg in Germany where he accidentally did not turn off reverse on his controller. He uses airbrakes which are enabled by reverse trigger input. There was delay in he reaction of the controller, but when it started reversing the prop the tail popped up and caused the boat to hop severely. I cannot recall if he stuffed, but reverse or braking was not a good idea.

[Fluid]

Back when we used brushed motors and round cells, and FE SAW records were under 65 mph, Jim Auguston set many hydro records using an ESC with a brake. It worked for him when running on small lakes, but the high weight of riggers back then combined with the ?low? speeds apparently held the tail down. Chris Harris was the first I saw using air brakes on a rigger to be able to go 100+ on little Blue Lake in Valdosta and stop without hitting the bank. They were clamshell vanes on the sponson booms. Worked well too....



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