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Old 02-18-2009, 07:14 PM   #1
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Guys,

I've been on this forum for almost a year now, since I bought a nicely upgraded MF from a dude in the States. Had it delivered to me when I was on vacation in FLA and took it home in my suitcase. If you search the gallery, you'll see the lovely job the previous owner did but I had other ideas in mind....

Anyone who's checked out MadRam11's videos on YouTube depicting the exploits of Tim Cameron in his awesome unit 7 buggy "Fat Girl" will never forget the sight of Tim fighting to climb a muddy hill with grit, determination and a 50lb right foot.THIS is what they call rock crawling in Tennessee!!

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

Other vids not to miss include "Fat Girl Wheely" and "Gettin Dizzy".

I guess you've probably got an idea of what I've got in mind now

I chose the MF as the base because the axles just seem downright bomb-proof. That and I loved the idea of the spiral cut diff gears. Current engine is a Team Infinity .30 which is pretty powerful but I want a transmission that'll stand up to more abuse. Currently the CEN 7.7 is appealing but I've got all kinds of ideas, not the least being a 10cc 4-stroke.

I haven't got much room ( or money! ) here, so I've decided to build the project in two stages:

Stage 1: Based on the existing New Era chassis. Remove the New Era bumpers, Convert the suspension to 4-link. Reposition the steering servo and change to BTA ( Behind the Axle ) steering ( possibly 4WS ). Extend the wheelbase out to 18+" ( 45cm+ ) and change the wheels / tyres. ( The current Imex Jumbo Maxx tyres weigh 520g each. That's almost 5lbs, just in rotating mass!!! What's more, they were very hard to balance. Holding my truck with anything other than zero throttle was like trying to keep hold of 10lb of epileptic otter!! I've elected to go for Proline Moab XL tyres but I'm going to convert them to 2.2" in keeping with the profile of Fat Girl's wheels- Let's face it, they're higher profile than Mr & Mrs Beckham! I also need more shock travel as that seems to be limiting articulation so I've lashed out on some shocks ( dampers ) from an HPI Savage XL. ( 160mm should be enough! ).

Stage 2: Once stage 1 has allowed me to figure out ideal sites for the link mounts and various other things - not least giving me more time to get money for this project! I'll fit everything into a custom built "tuber" frame. I'm quite keen to turn the engine round and run it in the front - Not sure why. Just like the idea. If I haven't fitted 4WS by then, I'll do that. My current steering servo is a bull-strong ACE DS1015 and I'd like to use another for the rear. That'll make this job a little pricey. Added to which, I still haven't figured out the fine points of the DX3 controller and haven't thought through how I'd control the 4WS.









OK. So where am I today? Well, I've made some progress - See the pictures. The 4-link is temporary at the moment. Both rear suspension arms were cracked where they meet the axle - May be due to concentration of stress in that area due to the New Era bumpers and reinforcing arms. I cut off the suspension arms and turned the tubes round so I have a few mounts for the lower links and shocks. Yup. There are 2 "jubilee clips" holding each of these to the axle. These keep the whole thing rigid and let me adjust things without having to drill new holes for fixing screws. The upper link mount on the axle is a variation on the theme of the mount Yotachump fabricated for his TwinForce. I've made it out of circuit board so far, so I get the shape just right before I commit it to aluminium.

The lower links are mounted onto a New Era skid plate modified to fit transverse rods - Not shown in the pics.

I've been working on the chassis design. Soldered a 1/4 scale mock-up out of 3/16" brass and copper tubes. FYI it's 23cm long and weighs in at just over 70 grammes. Wouldn't stand on it but it seems pretty rigid. Now I've got a good idea how the chassis will go together.







I got the Savage XL shocks and they seem to do the job. I'm getting closer to the ultimate stage1 4-link set-up. Keeping the off-centre diffs and using the diff centres as the 4-link mounts does present several headaches. Of course, the upper links are assymetric and this means that, when you're adjusting lengths, you can't just take 10mm out of each; You need to take a little more out of one than the other. Also, adjusting the driveshaft angles, caster angles, shock mounts and 4-link mounts simultaneously was quite a trial. You change one thing to compensate for an undesirable factor and that changes everything else. Takes quite a while to get things close to right. Then you find the diff isn't lined up with the gearbox and off you go again!





The Traxxas Summit / E-Revo driveshaft seems to fit together well although I'm not sure it'll stand up to the abuse. I'm planning to strengthen it with M5 studding and a short length of graphite tube. I managed to kill 2 carbide drill bits putting a hole in one diff pinion. Will have to take it easy on the others.





Articulation seems pretty good. Not quite 90 degrees but then this isn't a rock crawler so I'm pretty happy with it.





I mocked up some wheels and tyres just to get an idea how much it's grown. Wheelbase is spot on 420mm / 16 1/2".





Ground clearance is about 140mm / 5 1/2". That's more than I'm planning so I'll be making up some upper shock mounts to raise them above the standard New Era chassis.

Amazing how much you can get done when the family's away for a couple of days!

I'll continue to update on progress from time to time. If you have any helpful comments, I'd very much appreciate them. Of course, if you have any questions then let me know.

All the best

Rtz

R

Last edited by RootesMan; 02-18-2009 at 07:20 PM.
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Old 02-24-2009, 03:47 PM   #2
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Ok, first off your 4 link will not hold up. The lower links are too small, they should be a minimum of 3/8" material. I ran my stock TF with dual motors and two 7.2Vs and bent my lowers everytime I went out. Your uppers are, well, going to act, um, crazy at speed. Your roll center will be totally screwed up. Unless you are going to run circle track. If you are running Kyosho pinions you need to grind off just the case hardening before you drill them out. I used HSS drills on mine. If you are running HB gears don't even bother. They are chromemoly and yuh ain't gettin through em. The Revo shaft will hold up just fine. The torque strain we put put on them with our crawlers far exceeds what your nitro will put on them. 90deg articulation is too much for a crawler, so don't try to get any more out of it. Savage shocks are overkill. 100mm shocks work just fine. There is no advantage to 160mm shocks except a high COG. Your tube work looks very nice. Santa will be very happy with his new ride ;)

Oh yah, add posts instead of editing you original
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Old 02-24-2009, 04:57 PM   #3
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Thanks for the feedback BB. I've changed the upper link mount points back to the originals as per these pics.





Make a little more sense. Ya think?

The advice about the pinions would have been helpful a few days ago! That said, I used the broken drill bits as hex pins - Waste not want not! I managed to get through the pinions but that was quite a job.

I take your point about the link material, although they're actually M4 stainless studding inside. Will probably get some made up when I know the right lengths. The Shocks may be overkill but I need the length to keep scale. They're a tad soft at present with HPI's stiffest springs but that may be down to the weight of the current ( New Era 6mm thick ) chassis. I'm hoping the tuber will be lighter. Also, I'm working on new upper shock mounts that will bring the shocks more upright

If you've got any more advice, please keep it coming. This is my first full-on project and I'm sure I've got lots to learn.

Cheerz!

Rtz

Last edited by RootesMan; 02-24-2009 at 05:02 PM.
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Old 02-24-2009, 05:33 PM   #4
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Quote:
Originally Posted by RootesMan View Post
The advice about the pinions would have been helpful a few days ago! That said, I used the broken drill bits as hex pins - Waste not want not! I managed to get through the pinions but that was quite a job.
Sorry about that bud. Missed this thread all together
Quote:
Originally Posted by RootesMan View Post
I take your point about the link material, although they're actually M4 stainless studding inside.
That should hold up a little better. Time will tell;)

One other thing I forgot, why the 2.2 cut'n shut XLs? I am running 2.2 on my 1/8 CJ5 Scaler with Rock Crushers(5"). That converts to 40X17.6 in 1:1.
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Old 02-25-2009, 09:50 AM   #5
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...why the 2.2 cut'n shut XLs? I am running 2.2 on my 1/8 CJ5 Scaler with Rock Crushers(5"). That converts to 40X17.6 in 1:1.

Good question Bart. The original "Fat Girl" buggy has tiny wheels and huge tyres:



Guess I could have used 1.9" wheels and slightly smaller tyres but the XL's appealed and I had a set of 2.2" Rock Lizards sitting around. Right now, I'm using HPI Rock 8 beadlocks, which are IMHO useless. I'd give them a 3/10. The rings seem to be made of steel ( probably with a very think chrome plate ) and the screws are as cheap as they come. You may notice a blue ring on one of the wheels. That's a template I made up to cut out some better rings from 1mm ally. They're 70mm diameter to get the wheel / tyre size to scale.

Keep the comments coming. It's all good!

Cheerz!

Rtz

Last edited by RootesMan; 02-25-2009 at 01:32 PM.
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Old 03-01-2009, 05:17 PM   #6
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Okay, Time for an update.

We were riding (just a little!) high and the thing was sagging over like a drunk so I made up some upper shock mounts. Also experimented with a torsion sway bar, made up from a BBQ skewer and a brass tube. It's a tad stiff so it's stopped the sagging but now it's hard to get any articulation at the rear. The BTA steering seems to be working out well, even though the servo is held on with zip ties. We're gettin there!







Cheerz!

Rtz
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Old 03-05-2009, 04:36 PM   #7
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is that the NEWERA KIT OR IS THAT JUST A MADFORCE I AM WAY JELOUS I WANT T HIS THANKS FOR COMING OVER TO MY THREAD LIKE THANK YOU ALOT I REALLY AM GLAD I FOUND THIS LIKE WOW I THINK IM GONNA THRO MY TRUCK IN THE TRASH AN ET TO SEARCHING SIKE BUT WOW NICE <<<
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Old 03-05-2009, 05:59 PM   #8
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Well thanks mate! Yeah. It's the New Era Chassis. When I got the MF, it had the bumpers and axle-mounted steering and suspension reinforcing links. To be honest, once I've got the tuber frame built up in a few months, I won't be using any of it so I'll probably advertise it here. Don't throw your truck in the trash, Dude. It looks good. Take your time and you'll get what you want. If you're looking for a MF, I'm sure you'll find one. They're really very simple to modify. Fun too!!

A short update while I'm at it. Evrything was set for a shakedown today. Spent an hour or so wondering why the engine wasn't catching properly and then realised the rotostart adaptor case was cracked!! 2 out of 4 srew lugs cracked off , a long crack across another hole and the gears and bearing inside were completely knackered! Oh ARSE!!

Contemplating binning the whole engine in favour of an Axial .32 or a large 4-stroke ( say 1.5 ci ).... Watch this space.

Cheerz!

Rtz
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Old 03-05-2009, 06:56 PM   #9
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How is your axle lateral movement? Hopefully you have enough triangulation. By sagging do you mean torque twist? Your torsion bar is a good start. You may stiffen up your soft side too.

I vote for a 4S Lipo and a 2hp outrunner
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Old 03-08-2009, 05:30 PM   #10
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Thanks for the interest Bart. Recon I have enough triangulation. The chassis and axles are stiff enough sideways, but without the sway bar, it does have a habit of leaning over, even when stationary. The engine weight causes the CoG to be quite high and added to that the fact that it's off-centre means it does lean a little. I'll mount it lower in the tube chassis once it's built up. Just trying to figure out the best way to get it central. Haven't seen any torque twist yet as I haven't run the engine up since the new suspension was fitted. Thought I'd be shaking it down by now but have had trouble with the e-start adaptor - Broke 2 ears off the casting!

Cheerz!

Rtz
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Old 03-10-2009, 04:56 PM   #11
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Quick update:

The engine took a while to sort out. In the mean time I decided I needed a body to protect my delicate bits. Hope ya like...



Cheerz!

Rtz
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Old 03-12-2009, 07:48 AM   #12
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looks pretty sweet man. so is this going to an all around monster truck basher? i would assume thats a yes with the nitro motor still on there!
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Old 03-12-2009, 10:53 AM   #13
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Hi there Daytona! ( Lookin forward to Spring Break?! )

Thanks for the interest. Yeah, well, kinda. I'm working towards some kind of crawling capability, although, of course, it won't be able to keep up with electrics. I sure as hell ain't gonna be taking huge jumps. Guess it's more of a hill climber. Rather like Formula Off Road. Did you check out the Fat Girl video?

It's my opinion that mud, muck and gack are prerequisite. It never gets dusty here, even with global warming!:-P

Also, not to forget that, once the tuber chassis is fabbed, wheelbase with grow another 4 inches or so.

Cheerz!

Rtz

The secret to success is sincerity. Once you've learned to fake that, the rest is easy!

Last edited by RootesMan; 03-12-2009 at 10:53 AM. Reason: typo
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