Madmax160764

Crazy 52cc sprint boat...[link=http://www.youtube.com/watch?v=IHppDMbiGE0]52cc Monster Jetsprint[/link]

g master

kinda chagning subjects here but were can i buy a 1/4 jet sprint

headhunter23

Dunno dragon... I would bet you could do villain as a dual jet drive if you really wanted. There really is enough room in terms of width. Transom would be a nightmare, would be easier to shave the whole back underneath the step then use foam to contour the bottom then glass it. I would do 2 of those bottom hull angle pickups for cooling as it would be nice and clean. Problem would be batteries, you could no longer lay them along side the single drive as there would no longer be room. So the battery or batteries would need to be above jet, which would mean making a spot for them. That part could be tricky, making a little platform to receiver batterys wouldn't be hard but whether there was enough room to do so. I could ask my buddy to measure up his villain and let ya know but it could be a couple days to get that done.

the aeromarine hull... so far I would say don't get it, unless you can get a better picuture of the side profile of the bottom of the hull. You really want a nice flat hull at the bottom, you don't want a bit of a bubble that comes back to flat, seems to create skipping affect which needs to be cured by a single tab out back.

Ivan.

sundogz

OK, so this was a long time coming but I finally 'joined' youtube and posted movies of the improvements I've done on the ABC Kawasaki Jet Ski in chronological order. Please forgive the low resolution - they look better on my computer than on youtube, but it has something to do with my DSL connection (we had an ice storm recently).

First one is of the stock jet ski with 8.4v 4500MA NIMH battery. You can see how badly it cavitated, less so in the turns. Soon after this movie, it sucked up a pebble through the stock intake grate taking out the impeller. [link]http://www.youtube.com/watch?v=CSbtqCi7RtY[/link]

Second one is the same setup after the intake mods (increase intake area, installing 3/16" mesh cover). You can see it doesn't cavitate anymore and doesn't seem to adversly effect speed.[link]http://www.youtube.com/watch?v=4QlpTlEjo-Q[/link]

Third one is after installing a 50A esc and 3s 2800MA 30C Mystery battery. Stock 550 brushed motor is peppy![link]http://www.youtube.com/watch?v=109A8luy1Ls[/link]

Fourth one is same setup without the canopy/rider (Pat). Faster yet, but cavitates badly. It needs more weight [link]http://www.youtube.com/watch?v=ARjDPhKXHJ0[/link]

My next improvement will be a reverse bucket (from a Graupner drive?) When the COG is right (for quick planing), there isn't enough weight to keep the jet underwater to facilitate reversing. No worries. I've posted a couple of movies on the "Tear Into" thread of my knockoff as well. Hope you like.

headhunter23

Sundog... looking at videos, that thing glides extremely nice after turning off power. Seems more so than knock off. But you sure the cavitation is due to jet/motor? At this point I would say its the hull design that's gliding so well air bubbles are making it to intake.

Kinda weird... ur right though after putting on the grate, looks much better, shouldn't but does.

Ivan.

sundogz

Yeah, it's heavier than the knockoff, so will glide farther when shut down. Fooling with the center of gravity and removing that 'hump' behind the intake (which is open in the rear but goes nowhere - trapping air) helped out a lot. I suppose enlarging the intake made up for any 'obstruction factor' caused by the grate. Now it stays down in the water nicely (see ABCJS05). Unless of course, you remove the figure (Pat) - then there's not enough gross weight, and you'll get cavitation (ABCJS06). I'm happy with it now. I've bought another (again, what a deal! - includes a decent radio that will transmit as far as you can see it) and will be making the intake mod on it as well, and will post pics this time.

If anyone knows of a jet reverse bucket will work on this ABC jet (impeller looks to be about 21mm), let me know. I suspect the Graupner mini-jet because it has a 19mm impeller, but that bucket is only sold with the jet, I believe. I don't want to buy something I can't use or have to return. THX, Sdg.

areseaer

[link]http://www.cornwallmodelboats.co.uk/acatalog/graupner_2344_1.html[/link] I think this one is your only option.

headhunter23

Maybe try making one... shouldn't be that hard, just need something to go infront of exhaust and redirect flow forward. Get some aluminum, hammer and something to bend metal around. Heck i think you could make one with a drill and bend alumiunum by hand.

Ivan.

sundogz

I agree with you both. I was considering the Graupner 2344, but the mounting flange doesn't look like it would work. So I would have to make a different mount, and if that's the case, I might as well make the reverse bucket too.

I know one thing, some day soon I'm going to put that new #2395 Graupner propulsion unit on a boat. I like the way the intake is fully to the rear - good for 'stepped hull, mostly out of water' planing. The steering/reverse 'box' ain't too sexy, but I could get used to it (?]> or adapt another. Thanks, Graupner!!

But ouch; it and the bucket come to a hundred bucks! Gotta start saving up. Mo' money, mo' money!

grael

I've hand made scoops before,
Hamilton have a fairly good design.

If you use the jetski version, they are simpler, the reversing scoop fixes to the steering nozzle, and turns with it, therefore, the direction of side thrust always swaps over when the scoop comes down. A jetski reverses like a car, forwards/backwards, same circle.
On a typical jetski type reversing nozzle, you have to do the forwards/right, reverse/left, forwards/right, reverse/left sequence like in a car.


A Hamilton scoop is fixed to the outlet forward of the steering nozzle. A Hamilton scoop deflects the thrust to the same side as it was already going, so you can turn on the spot by balancing forward and backward thrust, while having steering hard over one side. It means that to do the equivalent of a 3-point turn, you only need to move the steering once, and balance the forwards/backwards thrust. I used to wire the throttle servo to the scoop, and I used a servo arm at right angles to this arm, with two mini pulleys, and a cable running from this arm, between the pulleys, to the engine throttle. This let me run with two channels RC sets.

To make a Hamilton style scoop, you need to have the scoop sitting above and around the jet just before engaging with the flow, to lift up a little more for normal running, to clear side thrust of jet, and when it's fully down, your jet should split evenly to the sides when centered, and curve out and down from centre, so the the reverse thrust just clears the underside of your hull. You also need to be able to run the steering over fully to each side, and have the reversing scoop deflect the full flow, back out the underside of the hull.

Because you have to clear the underside of the hull, there will be some down thrust, which will lift the stern, be aware that your boat may take a nose dive if it hasn't got enough boyancy at the bow.

edit:
You can make your scoop out of thermosetting plastic, ask for it at an art supply shop. Fimo is one brand I can think of now, there are others. You shape it like plasticine, and then cook it at a set temperature in a domestic oven. when it's cooled down, it's a hard plastic. You can usually buy it in a wide range of colours too.[8D]

sundogz

Thanks for the good info Grael. That brings up another thing to think about. I use an ESC instead of the stock servo activated 2-speed control. It has reverse, but won't work like that. Maybe with a bridge rectifier I could send the (reverse voltage) to a solenoid to lower the bucket. Something to consider there. There might be a more elequant way if I think harder (ow!).

DRAGONFIRE81M

some where in this long thread i have a way to do it if you have a brushed motor

grael

Sundogs,
It's easy:
Connect your ESC in parallel to your reverse scoop servo:

The servo needs power (4.5-6 volts same))m and it needs a control signal... same as the ESC control signal. Only thing is, you won't be able to trim the ESC and reverse scoop independently. Or use a 3'rd channel, if you have it.

DRAGONFIRE81M

here you go

sundogz

I dunno, none of that makes sense. When I change directions, my esc changes motor polarity. Are you saying hook up a servo in parallel to my motor? Hmmm. And if I use forward only mode, there is no signal when I push forward on the 'trigger', so it won't do anything there.
I have an Airtronics MX3 and could use the third channel, but would rather use the 2 channel radio that came with it if possible. I need to come up with a way to use that reverse polarity signal to operate a servo, and not effect the motor when that happens (motor still goes forward). Sort of like the throttle in a 3d helicopter, where center stick is full throttle and either way drops throttle (only backwards- center stick will be off). Ha! good one. That will get you thinking!

grael

Sundog was refering to an old post of quicks, in which it wasn't an electronic speed controller, but a switched electric one. Much simpler to modify.

I see what you are saying though, the electronic speed controllers don't generally have a centre off, unipolar speed increas either way off centre mode.

The servo control is fine.

How the control signal works, is a pulse width modulated signal. it varies from fully off, to fully on, and with a cycle period of about 2mS, if I remember correctly, one of the other guys who used to use PIC microcontrollers (David VanHorn) used to have some code on the internet for it. I think he switched to Atmel Microcontrollers, like me.

If you wanted a really simple way to hack a solution, then you could use a switch to pick up forward motion direction from your scoop servo, and use it to invert the same channel signal, before it went to the ESC. That way, as soon as you pass the centre position, the pulse width signal would look like it was going back up again, but the same way. A 4011 chip would work for this, it's a quad NAND gate, and will work from about 3v to 15 volts. On one gate, connect one input to the channel signal from the servo, the other input to the switch, (switches between 0 volts and radio reciever positive).

To use an even easier cheat, connect it to a wire taken from the centre pin of the potentiometer inside your reversing scoop servo.
The output of this gate goes to the control signal input of your ESC

If the ESC tries to spin the wrong way, then take two inputs of another gate inside the 4011, and connect them to the output of the first one, the output of this new gate will be the other way around and can be used instead, to control the ESC. Any inputs you don't use, should be connected to zero volts.

DRAGONFIRE81M

no you conect the servo with the esc by means of a y conecter so both the esc and servo gets the same segnal from the rx . heres the trick when you are in forward moson the servo is going to try and pull the bucket up more then itsw going to alow so youll have to put a sping on the push rod . so whn it does this it will only compress the spring and not try an rip the bracket apart .

grael

Dragon,
Your way, the ESC will never be able to get full power reverse, and the transition point between forward and backward will be at some middle throttle setting.

I didn't need springs Dragon, because I set the servo arm and reversing scoop arm angles so that full servo motion was allowed. The scoop going up it not usually the problem, but you need more power to drive the scoop down against the flow, and you don't want to drive it too far down either.

So, you set your servo arm to have the most leverage, at it's end of travel, in the direction that pushes the scoop down. The scoop needs to have it's arm at right angles to the control rod at this position for maximum leverage of the scoop, where as the servo arm will be almost in line with the control rod. Then, as you drive the scoop up, the motion will become faster, with less force, as the scoop rises to it's maximum height.

damfurst

Hey Sundogz, I have a reversing bucket from a graupner mini jet you can if you want it. I'm not sure how you mount it since it uses 2 little posts on either side of the rear of that drive. But if you want it pm me.

sundogz

Oooooeeeeee! I really opened a can of worms here. Yes those are interesting theories, and since we don't have a working model, allow me to share my theory (I slept on it some). It goes back to my earlier suggestion:

1. put a full-wave bridge rectifier (diodes) in the line from the esc to the motor (brushed). Now you have forward motion (of motor) for both directions of trigger movement. (I don't know if it needs to be full wave, just a bridge might work)

2. On the 'reverse' limit side of the rectfier - parallel with the motor, put a low voltage solenoid in series with a low ohm (10-100 ohm) 1 watt resistor (to limit current). (My figures are guesstimates and meant to explain a theory only).

3. Now, when you go 'into reverse' the solenoid can pull the (spring held) buckets down, (you'd need a low limit block here) or by use of a cantilever or pivot (servo arm) and piano wire - 'push' them down.

Hope I explained that well enough. That's as feasible as any I've heard so far, but are just theories until someone does the build. Thanks for all the suggestions anyways.

Dragon, have you ever used a 'y' connector that way? (from the receiver to both the esc and a servo)? If so, what happens? (just wondering - never done it). If it does work (both at once) we still have the problem of the motor going backwards or dead in the water (depending on esc setup for reverse).

Damfurst, will you hold that bucket up to your ABC jet drive and determine if it should work or not (large enough). If so, I'll be glad to take it off your hands and try it out. Thanks, Sdg.

areseaer

HPI has a reverse mixer for their savage. If your can disable reverse on the esc it would work. I think in the savage you hold full brakes on for 3 seconds and the mixer moves a servo to engage reverse. [link]http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXMGM3&P=7[/link]

DRAGONFIRE81M

thats pretty good find aresear . and yes sundogz the servo and esc work together with the throttle at dead center on the tx the servo will be at dead center also . if you move the trger to forwardthe esc will ingage and the serco will move to one side

grael

sundogz:
interesting ideas you have, but there are some practical issues with getting it to work:
1) you are right, that it would take a full wave bridge rectifier to work. Diodes have a forward voltage drop of around 0.7 volts. Using a full wave bridge rectifier, you have two in series, this works out as 1.4 volts. say you are using a 14 volt LiPo, that's 10% power lost already, to the FWB.

2)a FWB big enough to handle say... 50 amps, is pretty large. If that's the sort of current you are running, then you will have
1.4V x 50A = 70 watts wasted across the FWB as heating. That requires a lot of of cooling, else it will melt a hole through your hull. Expensive, and effectively downgrades your run time/power, while making the boat heavier to boot.

A better low tech approach is to use a high current DPDT relay to switch the motor back into forwards, when it would otherwise be running in reverse. You'll be struggling to find one that operates off RC voltages though, you can find 12 volt ones though. It will need a diode pointing from negative of the coil to positive of the coil, to stop your RC receiver from frying. The volt drop across a relay contacts is negligible.

3) The solenoid idea... the "sweet spot" in a solenoid, where it has maximum operating force, isn't very long, maybe 10mm. You would a BIG solenoid to overpower the jet enough to force the scoop down. Servo motors are geared, hence their small size, and relatively high control forces. Same thing as a relay... diode across coil, pointing from negative to positive.


You wrote to dragon:
"Dragon, have you ever used a 'y' connector that way? (from the receiver to both the esc and a servo)? If so, what happens? (just wondering - never done it). If it does work (both at once) we still have the problem of the motor going backwards or dead in the water (depending on esc setup for reverse)."

It's fine. the control (white) wire is an output from the receiver. It can control more than one servo and/or ESCs
But... as in my post above, you need to detect the halfway point (i.e. servo potentiometer voltage halfway between 0v and 6v, and then invert the white wire signal going to the ESC. That way, the pulsewidth modulated signal will have the lows swapped with the highs, and the times will as a consequence, swap also, so that an increasing off period would become an increasing on period. Only sticking point, would be that some ESC probably have a non zero centre position.

Edit: here's how you would wire it:
(dir1 and dir2 are connection options to let you match the motor direction relative to the scoop motion direction.)

sundogz

You are probably right - it would take a large rectifier, and would be quite inefficient compared to the great idea Areseaer had (HPI reverse mixer). And I sure don't need complications - the less parts to git 'er done, the better. But holy cr*p, I just checked and my 'inexpensive blue Chinese finned waterproof 50A esc' cannot be programmed (for only forward) and detects/sets itself up. Argh. I do like it though, especially the cool sound it makes. I'll figure something out.

Dragon, thanks for that info - I never knew what would occur. That's good to know...opens up possibilities. Sdg

headhunter23

Mmmm... two videos.. seems delta jet needs some work to bring hull up as she doesn't like combating standing waves. Apparently through them like mini me is the way to go.[:@]

http://www.youtube.com/watch?v=WeSnhxB-Sww

Also buddies jet villain and knock off didn't do so well on -20 day(wind chill and man I mean chilly)... new nemisis is ice, not just leaves!![:-]

** think this is the link but unconfirmed at time o post...
http://www.youtube.com/watch?v=3C3ilsmorto

Idea for delta jet is to pull out bottom of mounting nozzle out a couple degrees and epoxy the difference... can't think of any others simple ideas.[]

Ivan