converting vintage MRP hydro to brushless

[Lurchalicious]

First and foremost, hello! First post for me.

Saw some members here that have done the same work on older hydros and hoping for them to chime in as well.

Looking for some guidance - I come from electric rc truck in the middle to late 90s. Worked at a hobby shop. This MRP hydro came in and I picked it up, tried to get it running and then my short attention span back then diverted my attention back to the release of the hpi rs4mt (trying to date myself for reference :))

My questions:

I'd like to convert to a lighter brushless system from the dual brushed. Looking for tips on motor combination / prop suggestions?

Should I consider water-cooled jackets?

When converting to a higher power system like this what would I need to keep in mind with the hull? Should I put some reinforcement in with fiber sections?

Lastly how do I balance this, should the cg be over the motor?

Some pictures :



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[ray schrauwen]

Don't spend too much on it because over time plastics break down and become weak. Adding too much power will just see a quick demise at the bottom of a pond.

A single motor like a Leopard 3650 will do. The choice of RPM and voltage depends on where you are able to get your COG. There is a lot of space limitations in there for 4S or a pair of 2S packs.

[Fluid]

Welcome to the forum! The hobby is a lot of fun, but you may have bitten off too much for your first build. These boats never ran well when new, club members raced a couple in the early 90s but had to do lots of mods. A terribly designed drivetrain! I bought a bare hull to build up, but between the leaks in the unsealable hull and the lousy bottom design I never was satisfied with the results. The last year or so of production they completely redesigned the boat with a real gearbox, flex drive et al but it was too little, too late.

As above, nearly 30 years on the ABS is now brittle and will not take much abuse without splitting. Not sure if applying fiberglass would help, it would just crack at the edge of the glass. If you insist, a 4S limited motor/ESC/pack setup will be enough. Don't know if it is worth the trouble to convert to a flex system. A 36mm motor with Kv between 1500-1800 and an x445 to x447 prop will be plenty. CG as close to the sponson transoms as you can.


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[Lurchalicious]

Welcome to the forum! The hobby is a lot of fun, but you may have bitten off too much for your first build. These boats never ran well when new, club members raced a couple in the early 90s but had to do lots of mods. A terribly designed drivetrain! I bought a bare hull to build up, but between the leaks in the unsealable hull and the lousy bottom design I never was satisfied with the results. The last year or so of production they completely redesigned the boat with a real gearbox, flex drive et al but it was too little, too late.

As above, nearly 30 years on the ABS is now brittle and will not take much abuse without splitting. Not sure if applying fiberglass would help, it would just crack at the edge of the glass. If you insist, a 4S limited motor/ESC/pack setup will be enough. Don't know if it is worth the trouble to convert to a flex system. A 36mm motor with Kv between 1500-1800 and an x445 to x447 prop will be plenty. CG as close to the sponson transoms as you can.


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That's decent insight, I hadn't thought about the age of the abs . I'd hate to just be chasing the dragon making this work.

This lake behind me however is begging for rooster tails...

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[AndyKunz]

I had one of those. I did a number of mods to it, including a .12 nitro, improved ride pads, and an automotive clear coat. It was a lot of fun, but eventually the stresses were visible. It's been on my shelf ever since.

Andy

[grsboats]

I would just use lipo batts to have fun...agreed that any investment doesn't pay off for an old plastic hull.Gill

[JestDanny]

If you go brushless you can use a motor with 5mm shaft. Car pinion metal gears fit jest fine, use two Robinson racing products 25 tooth, get the 5mm to I/8 shim for drive gear. I've been workin on same project. I acquired the U-31 Circus Circus boat. Mixed results an very limited winter testing. I trying twin 2 cell, one each side for balance. Mostly its for lookin at, shelf queen, but its gota run at least once an a wile jest because it can. Hope spring arrives soon, stay tuned.SAM_2435.jpg

[JestDanny]

oh yea the 36 mm motors bolt right up, but not enough clearance for water jacket. So if go that rout pick a motor that can run without water cooling. I originally tried a Dynamite pro boat 36 mm, 2000kv 2 to 6 cell motor with the 25 tooth metal car pinion gears, had to remove water jacket to fit. The boat showed promise in the one brief winter test I managed running x435 prop. I'm building jest for sporting fun, during the test I jest got it up on plane with out pushing to hard, still learning to drive hydro's. After the test in my humble opinion, boat seemed a little over powered, for age, design, size, motor seemed a bit warm too with no cooling, so I removed that motor, ESC combo, going a diff rout. I went to a 28mm motor, I carefully drilled the mount so the motor sits centered directly above drive gear, water jacket fits now, 1/8 motor shaft so I went back to original plastic gears. Again jest one very brief failed winter test, running a x432 prop, stuffing tube came loose ending test. Now jest waiting on spring for more testing. Shelf Queen has to run at least once or thrice a year.