1/10 Crackerbox brushless build

[befu]

OK, so I have these 1/10 scale crackerbox hulls that we are going to be building with some of the cubscouts. The boys are 8 years old and for most this is there first non-walmart electric boat. So, this is what I am looking at doing:

Edit: The ebay link got old, so here is where I have been buying them. Ebay, seller name is cyberport888 and go to his store. He has the 1700 and 3000 kv mystery outrunners with 30amp esc for $19 to $21 delivered.

Mystery 30 amp esc and D2836-1700 brushless outrunner motor for speed. On a 3s battery and a x431 plastic prop, I figure speeds should be around 20 mph or a little higher. (18,800 rpm no load)

The hulls are plastic, with a 8.5" x 11" kevlar/carbon inlay. Transom is 1/8" hard plywood and the front of the hull will be solid foam. Weight with hatch is about 12 oz.

Drive will be traditional solid shaft, but they will have a flex shaft coupler on them for ease of driveline install and to limit vibration. rudder on transom.

So, anyone offer any advice on if this will work? Locally, we will build them all the same and race them. Not out for top speed, just some fun on a 3 acre pond to teach the boys some skills. Would love some feedback. I do not know how these run with the Roar motors and 6 cells. What kind of speeds do they get verse run times. I know in race trim, blowovers are the main issue. I want them to have fun, but not be flipping them constantly.

Oh, I am donating the hulls to the other boys, should be able to keep building cost down to $100 or less with 2 batteries and a cheap lipo charger from HK. Two of the boys need radios, will be postin a WTB add for some 2ch AM radios.

Thank you to any who can offer advice,

Brian

[j.m.]

Sounds like a great project, and I may be able to help with the 2 ch. AM radios...

Jon

[bwells]

Good idea and you will have your hands full. Hope you will have some help if only a few sets of eyes to lookout for what can go wrong. They will be on their way to Eagle Scouts! You mentioned 3s and then 6 cell and then 2 batteries. Is the 2 batts 1 for a spare or in parallel. The 6 cell you mentioned I'm guessing NiMH as opposed to 3s in series. The ESC is 12volt so I think the 3s would be great once the kids learn to drive but maybe start them on the 7.2 NiMH to learn and then throw in the lipo and watch their eyes light up! Good luck and a good price on the ESC/motor combo. Keep us posted please

[befu]

Good idea and you will have your hands full. Hope you will have some help if only a few sets of eyes to lookout for what can go wrong. They will be on their way to Eagle Scouts! You mentioned 3s and then 6 cell and then 2 batteries. Is the 2 batts 1 for a spare or in parallel. The 6 cell you mentioned I'm guessing NiMH as opposed to 3s in series. The ESC is 12volt so I think the 3s would be great once the kids learn to drive but maybe start them on the 7.2 NiMH to learn and then throw in the lipo and watch their eyes light up! Good luck and a good price on the ESC/motor combo. Keep us posted please

sorry about the confusing post.

I am planning on running these on 3s lipo. the IMPBA and NAMBA classes use 6 cell standard batteries, or 7.2v with a Roar legal brushed motor. I do NOT want to go brushed! Just wondering how fast those run in oval trim racing.

I want to build them and have two batteries, one for a spare for running time. Might need to parrallel them for ballast if needed to hold the boats down, no idea on how fast they might be.

I have plenty of 2s-2200 lipos, so for the first run or two could set them up that way, then give them thier 3s batteries!

Might have to watercool the ESC, that would be another good project for them.

Brian

[damfurst]

Man Cubscouts was never like this when I was one. All I can remember doing was glueing burned out matches in a pattern and making something with glue and popcicle sticks. I may have a couple of 27am radios & receivers that I would donate if you need them. Just let me know.

[bwells]

Brian, Okay, I understand. Did the crackerboxes have a turnfin in the keel towards the bow or was that the old drag boats? That might be a thought as opposed to 2 turnfins on the transom. These are flatbottoms, right?

Brian

[befu]

Well, some of the boys seem to be getting bored, don't blame them really. There are all kinds of thier activities that we can center around these boats, even when it comes to safety and emergencies and how to react. Lots to teach from building models to art work on the hulls. When I showed them the boats, even thier dad's eyes sparkeled!

I have been watching and buying good 2ch am radios w/ rc for under $20 each, so if you can do that or better, I will take them.

The crackerbox is pretty flat. 6 3/8" wide with 3/16" deadrise per side. Not pancake flat, but pretty dang flat. They do have centrally mounted turn fins about midship also, nothing on the transom except basic trim tabs and a rudder.

thanks, Brian

[wakeboardfusion]

where did you get the hulls at, or did you make them. This should be a great project. Man that motor and esc are cheap! I bet these boys will have big smiles on their faces. I remember one time we made sailboats and raced them in raingutters on sawhorses... Times have changed.

[befu]

where did you get the hulls at, or did you make them. This should be a great project. Man that motor and esc are cheap! I bet these boys will have big smiles on their faces. I remember one time we made sailboats and raced them in raingutters on sawhorses... Times have changed.

I made them.

The rain gutter regata, have some of those little sail boats around still also. tomorrow is the pine wood derby race, should be fun.

[bwells]

Use lots of graphite on those pinewood derby's
axles! Nice job on the boats, do you have any pics of the bottom?

Brian

[befu]

bottom pics

Use lots of graphite on those pinewood derby's
axles! Nice job on the boats, do you have any pics of the bottom?

Brian

Well, cars didn't do so well. In fact, they were about 0.5 to 0.9 seconds slower this year than in the past. Worse we have ever done, but the kids had fun. Generally, one of my kids is in the top 3, but kinda waited to long to put them together, another chance next year.

Back to boats, here it is:

[j.m.]

And how could one get one of these??

[befu]

Progress

OK, the boys have been working on the boats a bit. Last week we cut the bottoms for the stuffing tubes and glued them in with CA and epoxy. They are 1/8" shafts with 5/32 brass bearings on each end in a larger 3/16"outside tube. To make the shafts, I threaded the prop end 5-40 for the nut, and drilled the other end out to .098 to .25" deep. I then glued a piece of .098 flex into the end so it will stick out of the stuffing tube and into the motor coupler. the shaft is located to allow up to a 35mm prop.

The motors are the mystery outrunners, 1700kv. Around 18k rpm on 3s lipo. The mount is simply bent aluminum. A turned a teflon washer to sit in front of the coupler. I may water cool the motor mount by attaching a piece of brass tubing to the bend section under the attachment bolts. It lines up nice and the flex will be nice and smooth running instead of a solid attachment or ujoint.

The esc's are now attached to aluminum plates with a water tube going through them. paste on the fets, pressed cooling plates onto that and then sealed in epoxy. should be nice and water tight. Not a whole lot of cooling, but these are not all out race boats. More of a crackerbox nascar setup!

Servo mounts are all done and ready to be epoxied into the hull. this week we should glue in the motors, the servos and hopefully we will cast the rudder brackets. I now need to vacuum form the hatches, that plug is done and hopefully works!

I have a few more batteries coming in to try out also, not sure if I will go cheap nicad or cheap lipo. Need to run one first.

the hulls are really strong with the kevlar and foam in them. Way overkill, but they are 8 year old boys!

Anyway, here are picks.

[befu]

No idea really comes to mind

And how could one get one of these??

You have radios, I have an extra hull...... hmmm.......

If only there was some way to work that out.......

Brian

[tiqueman]

Brian, now youve really got me wanting to build another one of these. I built one my junior year of high school ('92-93) as a Drafting project to enter into the state fair for the Technology Students Association (TSA) club. I found the plans in the back of a Boat Modler Mag that were about a 4"x 4" size. The project was, to learn how to accurately scale it up from that drawing and duplicate it in AutoCad. I learned how to accomplish that and built it. Lately Ive been thinking of building another as this was the first RC boat I had ever had that wasnt purchased at radio shack (or equiv.) Knowing what I know now, Id love to build another and right the things I made wrong... unfortunately, this boat took a hit while falling off a shelf years ago and cracked the port side. Theres is no glass or epoxy anywhere on it, except to glue things together.. and even most of that was just CA. I only ran it a hand ful of times before I got into gas boats.. but it was a cool little boat and I was pround of it no matter how it ran. Oh and I got 1st prize at the FL State fair that year.

Not looking for a hull, but I will see if I can come up w/ a radio and rx to donate to the club for the kids... Ive got a lot of misc Am stuff lying around.. I will see if I can get anything to match up and work....

Keep up the good work.. I was thinking about doing a similar project in the neighborhood I live in and getting the kids to meet up at the clubhouse twice a week to build something.. probably not powered though... something they can wind race or just put a small brushed motor to a couple duracells or somethign and let it go across the pond (about 40 yrds that one is) next to the club house... I dunno, still too many thoughts before I approach the event coordinator about it......

-Scott