LAV-25 - Watercannon rebuild

by **Jarlath** » Wed Sep 23, 2020 2:03 pm

So I recently acquired one of the old LAV's that had the water squirt gun in the barrel. It has been present for the last several years to squirt many unsuspecting children that are too close at larger public RC tanking events (example: Aquino Tank Fest in Oshawa, ON, Canada).

I had repaired it once previously with the existing drivetrain, the main issue is that when full of water, the LAV is too heavy to move and striped the Drive Hubs from the axle shaft, and once fixed, the gearbox itself. Long story short, driveline toast, control board corroded to hell = dead.

It was literally dumped into my hands and was told, "Its yours if you want it." So of course I said yes.

I had looked at the concept of a complete rebuild after the first time I fixed the unit... When it became mine, I bought a WPL 6x6 for the starting point of the build.

: Initial Driveline concept...

: Basic frame concept

: Showing Steering design

: Wheels and underside removed

: Frame in rough position

by **Jarlath** » Wed Sep 23, 2020 2:06 pm

Now to find more tires and steering axles...

The truck will be a 6x8 due to the required space for the motor gearbox... The question is if I get another 6x6 to make it a dual motor (Front 2 axles driven by one, rear two by the other.)

I still plan on this being a water squirtgun as well

I'll spread out the water tank portion across the lower hull for better distribution of mass.

by **midlife306** » Wed Sep 23, 2020 8:24 pm

I’m sure Will could sort you out with a compact dual motor setup

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by **Herr Dr. Professor** » Thu Sep 24, 2020 2:31 am

You list yourself as an "hydraulic systems designer." No wonder you want it resurrected to squirt water. I would love to see that in action when kids are watching. What fun!

by **Will01Capri** » Thu Sep 24, 2020 12:56 pm

I heard dual motors lol

by **Jarlath** » Thu Sep 24, 2020 4:00 pm

Will01Capri wrote:I heard dual motors lol

LOL... I have heard that the stock plastic gearbox/motor combo is pretty weak and prone to breakage...
Are the twin N20 systems better? I have ordered a second donor WPL 6x6 kit for parts (I'm sure I'll break something). And for the possibility of running twin original gearboxes albeit using only a single output shaft each (one for rear 2 axles, another for front two axles).

by **Will01Capri** » Thu Sep 24, 2020 5:53 pm

Jarlath wrote:
Will01Capri wrote:I heard dual motors lol

LOL... I have heard that the stock plastic gearbox/motor combo is pretty weak and prone to breakage...
Are the twin N20 systems better? I have ordered a second donor WPL 6x6 kit for parts (I'm sure I'll break something). And for the possibility of running twin original gearboxes albeit using only a single output shaft each (one for rear 2 axles, another for front two axles).

I developed a twin 180 and a twin 370 motor setup. They are strong and powerful and can be spec'd for speed and torque.
If you want I can share videos of both, but axles and driveshafts must be metal as they destroy plastic gears and flimsy driveshafts in seconds.
Please do not use n20, these are very noisy and very weak

by **Jarlath** » Thu Sep 24, 2020 10:48 pm

Yes please.

by **Jarlath** » Fri Sep 25, 2020 12:49 pm

: Tools of the trade for fabrication...

Cutting by hand is such a pita some days... I really should invest in a mini-table saw...
Maybe a Proxxon 37006 KS 115 Bench Circular Saw or similar...

: Basic sizing, 2mm sheet, cutting 36mm side walls.

Just a old school Vernier caliper for measuring... No fancy digital here.
Read the graduations! READ THEM!

: The side walls cut off.

: Layout of floor

Basic straight lines are pretty simple, but when I start having to do coping or more intricate details.
Layout is key for me. Make a simple template, go scissors!

: Trial layout on the remaining lower hull. More cutting to be done...

: Layout material for prep and template. Note the trimmed 2mm styrene floor.

Thankfully I have an ample supply of cardstock for layouts.
And way more from my place of employment. (They literally throw these away!)

by **Jarlath** » Fri Nov 06, 2020 1:24 pm

A small bit of advancement (My buddy Chris from NY sent me some spare axles and a whack of spare tires/rims from Dean = progress.)

Still unsure If I'll reused the old water tank. It fits. Barely! Trimmed down the existing water cap with the "tire" and fit it into a WPL hub completely. A Full sized spare!

Yes that is a "full size" spare tire now used as the water cap for the tank portion. I think it looks good. I'll likely have to limit turret travel now however.

How it looks with the upper hull loosely put into place. RAR! Upper hull will be the last pieces to be revised/rebuilt/tampered with...

Adding in the 2nd servo for steering since all the other concepts for single servo/dual steering were lack lustre in final forms.

Rough concept placement for the 2nd drive motor (Mounted one with heat sink drives the front wheels)

Steering linkage under the chassis in it's final configuration.

Again rough concept of the existing water tank space claiming. It is a VERY tight fit... May need to be modified.

Side shot showing the height. I may also need to use Heng Long rotation units due to possible interference fron the new drive motors.

Showing the conceptual test of steering with a "final linkage solution"

The driveline test! Both motors hooked up to a 6V battery pack (4xAA). You can see the tails of the Z-bends in the steering linkage video above. Forgot to trim them and they fit right into the universal joints of the driveline. (Whoops. Now trimmed down to avoid interference)

by **Jarlath** » Fri Nov 06, 2020 1:35 pm

Using 3D printing as a easily modifiable medium for design concepts/alterations. (Aka cutting out for servos and driveline axles, etc...) Just a quick simple exacto knife application and BAM, 30 seconds for alterations to the concept. A 2mm thick print is easier to sculpt than 2mm styrene sheet!

by **Will01Capri** » Fri Nov 06, 2020 1:41 pm

Looking good
Are you still using plastic driveshafts? If you are hauling weight then you will get those plastic things popping off all the time, go for the cheap metal looking ones which are quite blocky. There is a cv type which look nice, but they are not as long lasting, although they do allow larger drive angles, but you don't have that issue in your setup.
Steering setup is all cool, looks nicely sorted. Those metal 370 setups are great, i have a few in smaller models, are you going to connect them together or have them seperate so there is more of a differential setup between them?
That's going to weigh quite a bit if filled with water

by **43rdRecceReg** » Fri Nov 06, 2020 1:42 pm

Very impressive for a first attempt, especially considering the complexity of the engineering and, consequently, the number of potential trouble spots. :thumbup:

Following along, with a measure of admiration.

by **Jarlath** » Fri Nov 06, 2020 2:33 pm

Will01Capri wrote:Looking good
Are you still using plastic driveshafts? If you are hauling weight then you will get those plastic things popping off all the time, go for the cheap metal looking ones which are quite blocky. There is a cv type which look nice, but they are not as long lasting, although they do allow larger drive angles, but you don't have that issue in your setup.
Steering setup is all cool, looks nicely sorted. Those metal 370 setups are great, i have a few in smaller models, are you going to connect them together or have them seperate so there is more of a differential setup between them?
That's going to weigh quite a bit if filled with water

The first driveshafts right from the motor/gearboxes are metal already. (Thanks Chris!) I don't think I'll need one for the front driveline.
As the middle axles are the main axles that see input torque I had to ensure that I was beefing them up already. We'll have to see if the trailing rear axle will need the metal upgrade since it is slightly delayed in torque transmission (gear and driveline slop).

I actually was looking at 3d printed steering track rods at first due to the lack of driveline clearance and home made z-bend/loop rods for the steering linkage. I then found a set of rod ends from a micro Helicopter which were perfect for the linkages and the offset allowed me to re-used the WPL track rods.

I'm going to connect the 370's together. Debating on the need for the heatsinks (I'll be putting cooling fans in this anyways). If a single 30A ESC will work then great, otherwise I'll have to look at separate harnesses/channels for them. I'll also be beefing up the wire to a heavier gauge incase of higher current draws (maybe 20 AWG).

by **Jarlath** » Fri Nov 06, 2020 2:39 pm

43rdRecceReg wrote:Very impressive for a first attempt, especially considering the complexity of the engineering and, consequently, the number of potential trouble spots.
Following along, with a measure of admiration.

This is why I love RC vehicles. The mechanics. Like I said, I love design and tinkering. I leave the detail work/painting to those that are good at it. (I haven't painted a model in 15+ years...)
I'm still debating if I'm going to give this a magnetically attached upper hull like in my tanks...
IF the existing water tank becomes a space claim issue, then I'll make custom tanks that fit into the upper hull and distribute the water mass across a greater area to lessen the driveline stresses in the rear of the tank.

by **Jarlath** » Mon Mar 22, 2021 5:53 pm

It has been a bit, but I have re-started the LAV-25 as I take a short break from re-engineering DGSSelkirk's 1/10th Hooben PoS Hetzer into something decent...(LOL)

Found the base RC tank on a whim...
https://www.ebay.com.au/itm/1-16-Scale- ... 4625342467
But GD! That's nearly 125 Euro/150 US for the TOY grade base tank!!!

by **Estnische** » Thu Apr 08, 2021 10:28 am

Looking good. Should turn out to be a neat conversion with some added detail.

by **Jarlath** » Thu Apr 08, 2021 3:07 pm

Estnische wrote:Looking good. Should turn out to be a neat conversion with some added detail.

Hope so. Converting the upper hull to be the water tank itself and needing a new water pump due to size constraints.
Go figure the toy grade version has a ton of space inside, but add in a full driveline... and twin drive motors... Sigh.. Shoehorn time!

LAV-25 - Watercannon rebuild

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