Jebster's 10x10 HEMTT rollback hauler
 

Decided on my next project. I have a 6x6 so I decided the next addition should be big. And I've always liked the look of a HEMTT so I'm combining the projects. It won't be true to scale but something different.

Drivetrain is going to have each axle separately driven off a single shaft that runs down the spine of the truck. Each taps in via a separate transfer case with another transfer case reversed to connect in the transmission. Yes, that is 6 transfer cases. Thank goodness for cheap ebay products from China!

I already did a little mockup of the body using my favorite material, cardboard. I don't think it came out too bad for 30 minutes worth of effort. I want to find a body or have one 3d printed (saw files on thingiverse), which I feel is going to be the most cost effective solution.

The bed is going to have a screw drive to rollback the bed. Not sure about the tilt mechanism yet.

This build is going to take a while as I still need to get some parts and I have a couple other projects I'm working at the same time.

Here are a few started pics.

Re: Jebster's 10x10 HEMTT rollback hauler
 

Cool project, jebster.
I think what you're after is an M1074/1075 Palletized Load System, PLS. They're more or less a rollback that can detach it's flat bed or load.
Also the front 2 axles and the 5th axle are steer axles. In real life they don't turn for sh!t, but it might help in scale since SCX 10 axles have way more steering through.
Good luck with your build.https://uploads.tapatalk-cdn.com/201...723dd7d830.jpghttps://uploads.tapatalk-cdn.com/201...3632cc8f1d.jpg

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Re: Jebster's 10x10 HEMTT rollback hauler
 

I've considered building the PLS for mine as it could be used to load/unload a flatbed for hauling a truck. the challenge is i feel i would need some type of hydraulics to get enough lifting power and i'm not prepared to go that far.
i ididn't realize the 5th axle also steering (I've only been around the 8x8 versions). something to consider. i don't have high expectations for turning radius on this one but every little bit will help.

looking forward to getting some build time on this one.

Re: Jebster's 10x10 HEMTT rollback hauler
 

i did have a question for the other rcc members. given the transfer cases in my setup will cancel out and provide a 1:1 from the input to the axles i wasn't sure what transmission would be appropriate. i could always drop in an scx10 style transmission but in the interest of space i was considering a GRU. if i went that route what ratio would be the best? i was thinking 5:1 with a high turn motor might work but i want to make sure this thing has plenty of low speed torque.

Re: Jebster's 10x10 HEMTT rollback hauler
 

I would consider making your axles pass through, since it's relatively easy to do with SCX 10 axles. That would give back some gear reduction and simplify your drive train.
If not, you would need a decent amount of reduction through a GRU. Maybe you could add a gear reduction transfer case into the drive line?

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Re: Jebster's 10x10 HEMTT rollback hauler
 

That would be complicated and expensive to pull off in scale with hydraulics. Might be able to use electric actuators, which aren't as expensive. It would be cool to see someone build a functional PLS or something similar.
I know there is a build on here where a guy used a New Bright CXT cab for a roll back, and used actuators to make the bed work.

Real PLS's have a lot of positive camber on the rear axle to make up for the limited amount of throw it can turn. Pretty complicated and failure prone in real life.

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Re: Jebster's 10x10 HEMTT rollback hauler
 

This is going to be epic!

Re: Jebster's 10x10 HEMTT rollback hauler
 

the CXT cab build is one I had looked at and will probably model some of the rollback bed features from that in mine. I've been working with electric actuators in some Tonka truck rc conversions i'm doing. they work but the power does leave something to be desired.

I've done pass throughs on my other 6x6 build so I wanted to do something different on this one. with all the transfer cases locked together it becomes a solid driveline so each axle gets power at the same time without any lag due to slop through a pass through.
you are correct that i'll probably have to go with an scx10 style transmission vs gru to get the necessary reduction.

Re: Jebster's 10x10 HEMTT rollback hauler
 

not sure it will be epic but i'm going to have fun trying! thanks

Re: Jebster's 10x10 HEMTT rollback hauler
 

I'm glad you're familiar with that build and the use of actuators.


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Re: Jebster's 10x10 HEMTT rollback hauler
 

to tilt the bed I would like to find a way to have it done without any powered components (actuators, servos, etc.). my idea is to have some type of dry piston that props the bed up as the screw drive slides the bed back. once the bed get about halfway back the piston is at full compression and forces the bed to start tilting up. kinda like a tent post pushing up the tent. with the right angle it could work and it means one less part to fail. this might put some stress on the screw drive but I can always beef up the motor driving that.

Re: Jebster's 10x10 HEMTT rollback hauler
 

This sounds like a solution.
Real PLS's set the bed completely on the ground by moving two sets of hydraulic cylinders in an arc. The first set raises the hook at the front of the bed to about 45* while sliding it back on rollers on the top of the truck's frame. The second set moves the hook further in the arc and sets the bed on the ground.
Pretty neat to watch. I'm sure you can find videos on YouTube. I'm trying to conserve data otherwise I'd look one up and post it.
This operation might be easier to pull off than making it work like a roll back.

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Re: Jebster's 10x10 HEMTT rollback hauler
 

I've found videos on this setup. I've even seen someone do it with an rc truck. it would be cool but I think it would require hydraulics to make it work, which i'm probably not going to try on this build.

Re: Jebster's 10x10 HEMTT rollback hauler
 

Had a little time yesterday to work on this rig. I'm using some aluminum c-channel for the rails. I drilled out mounting holes for the transfer cases (I did a number of extras in cases I want to make axle-to-axle spacing adjustments) and mounted them up. Dropped an ax2 tranny up front just to see how it sized up. I'm most likely just going to go with a standard scx10 tranny because I don't think I will need a 2-speed.

The one challenge this set is going to have is driveshaft angles. I will need short driveshafts (~65mm) and have the axles clocked a lot to prevent binding. That is ok for the rear axles but for the front I'm going to have to be creative. I'm thinking beeftubes so I can drill new c-hub mounting holes through the axle housing.

Next thing to work is the suspension links and chassis mounting brackets.

Re: Jebster's 10x10 HEMTT rollback hauler
 

Still waiting on a bunch of parts but I was able to pay out my link geometry. This setup provides a lot of travel for each wheel. Even the tamiya semi driveshafts I bought for nicely.
I do believe I want to go with a cantilever setup for the shocks so they are low and don't interfer with the operation of the bed. Only problem with that is I'm not sure what rocker arm to get. I need about 1.5" of upward travel. If someone knows whether twin hammers rockers or traxxas 1/16 summit rockers give that much travel let me know. I ask about those because I can get a bunch cheap (and with needing 5 sets the cheaper the better!).
Next step is to replace my lexan link mount plates with aluminum and then mock up the front steering axles. Those will be more challenging in that I need to have enough room to run panhard bars and steering links around the pumpkins and transfer cases. Should be fun!

Re: Jebster's 10x10 HEMTT rollback hauler
 

Getting a slow trickle of parts coming in but not enough to make big progress.

I am looking for opinions on tires and wheels. Given I will need 12 total (10 + 2 spares) and I don't want to break the bank what are the best options out there? I'm OK with no-name brands and ebay products from China. I would like 1.9 beadlocks (plastic or metal) and tires in the 120mm (~4.5") ramge. I saw some trx4 tactical sets out there for cheap I was considering. They are glued on but I could live with that for a decent look and compound.

Re: Jebster's 10x10 HEMTT rollback hauler
 

Made some more progress. Got the rear axles mounted with links. Have the front mostly done, just need to make a chassis mount for the panhard bar, which is going to have to weave a path around the pumpkin and chassis rails.
Ordered up 3 sets of cheap tires and beadlocks wheels on eBay ($100 for 12 tires nd aluminum beadlocks is not bad, even if the quality is a little low).

Next will be getting shocks figured out. If I can get some hard springs I might be able to have some installed laid down a little and avoid the cantilever setup. Time will tell.

Re: Jebster's 10x10 HEMTT rollback hauler
 

Check eBay for cheap tires and wheels. Chinese knock offs can be had for under 25 for 4 and offer very good traction

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Re: Jebster's 10x10 HEMTT rollback hauler
 

Got some tires and wheels coming in from China. We'll see how they work.

I got some time to work on the suspension and steering. The cantilever are twin hammers parts. Ran out of rod ends before I could finish the front axles though. Everything moves smoothly, just need to find some inexpensive shocks. The steering uses some tamiya semi steering blocks connected together and then to the servo.

Re: Jebster's 10x10 HEMTT rollback hauler
 

So the tires & wheels from China arrived and I'm pretty happy. Tire compound is good and the wheels seem pretty sturdy. Foams are soft but I'll run them for awhile.

Also started getting parts in for the rollback feature. My plan is to have the motor connected to the threaded shaft via a belt and pulley system. When the motor spins it will push or pull on the shaft which will be fixed to each end of the bed. Still have a lot of mock up to do but the ideas are flowing.

Re: Jebster's 10x10 HEMTT rollback hauler
 

A short video showing my first test of the screw drive system I'll be using for the rollback feature.

https://youtu.be/PxkhIfYlN48

Re: Jebster's 10x10 HEMTT rollback hauler
 

Also got a set of shocks to try out. I really like the small diameter and the resevor adds a nice look but they are a pain to bleed. Still not sure I did it right. I bought two pairs but I'm not sure I'm going to buy 3 more.

Re: Jebster's 10x10 HEMTT rollback hauler
 

Looks great sofar. You wouldnst happen to have a link to the shocks?

Re: Jebster's 10x10 HEMTT rollback hauler
 

Thanks.

I don't have a link but you'll find them on ebay if you search for xtra speed 70mm piggyback shock.

Just so you know I'm not happy with the shocks and will be getting something different. The reservoir diaphragm has no seals so it leaks. Plus getting the tube to stay connected on each end is tough. I ended up putting some heat shrink tubing on the small nozzles so the the tube had something to hold onto.

Re: Jebster's 10x10 HEMTT rollback hauler
 

I found some pretty neat 70mm shocks on feebay for like $22 for 4 and they work pretty well. Unsure of the name but they're blue

Re: Jebster's 10x10 HEMTT rollback hauler
 

More work on the rollback mechanics. Pretty much complete. You can see the white delrin blocks that the channels on the underside of the bed deck will slide on.

Also started thinking about the transmission options. I have a GRU I might try. Do people have any issues with these handling brushless power?

https://youtu.be/PxkhIfYlN48

https://youtu.be/fLwiAiLo8-o

Re: Jebster's 10x10 HEMTT rollback hauler
 

I personally wouldn't run a Novak brushless motor since they can only run 2S. That, and I don't think they're as smooth as a good brushed motor on 3S. Personal preference.

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Re: Jebster's 10x10 HEMTT rollback hauler
 

I believe the novak can run on 3s since it was paired with a goat 3s esc originally. As far as a brushed motor being smoother I have had a similar experience but a good sensored brushless does pretty well.

Re: Jebster's 10x10 HEMTT rollback hauler
 

I let the smoke out of a Goat 3S a couple of years ago. I had the system on, not moving or under a load, because I was setting end points for the steering and it went up in smoke. Since then I've been reluctant to put 3S on anything Novak even if it is rated for it.

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Re: Jebster's 10x10 HEMTT rollback hauler
 

I've had issues with their esc before (hence the motor) but the motors have always run strong. That being said I'll see if this motor is a good match for this rig.

Re: Jebster's 10x10 HEMTT rollback hauler
 

Continuing to make progress. I have all the suspension set up including the front two axles panhards and drag links. Got the rollback structure mounted to the frame and it tilts nicely. I also made some crossmembers to eliminate flex.
Cut out the bed to size it up. Width is good but I need to shorten it up to around 21-22".

The only issue I'm having is picking shocks. I need 10 so I'm trying to find shocks that won't break the bank. They need to be either 60mm (compressed) - 75mm (uncompressed) or 70mm - 85mm. Not finding much.


Getting close to needing the cab. I may need to make it myself!

Re: Jebster's 10x10 HEMTT rollback hauler
 

Looking good. If you can handle building the mechanics of this, you should be able to scratch build the cab.
That being said, my builds take forever because I am too critical of my own work when scratch building with styrene. It has to be anatomically correct or not at all.

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Re: Jebster's 10x10 HEMTT rollback hauler
 

Shouldn't have any flex with those beefy crossmembers "thumbsup"

Re: Jebster's 10x10 HEMTT rollback hauler
 

More progress. Got the rollback mechanics all functioning. Instead of adding a mechanical tilt I'm going to see if gravity can do the job. I added some shocks filled with 5k diff oil to make the tilt more controlled and prevent it from slamming around. I also included limiting straps to prevent the shocks from being over-extended. At the back of the bed there are some rollers I made that allows the bed to roll out once it contacts the ground.
I also mounted the steering servo so that is all working.

Getting to the point I will have to start working the body.

https://youtu.be/I_BDScTOqNU

Re: Jebster's 10x10 HEMTT rollback hauler
 

First off, GREAT build. Congrats.

You over simplified the ideal way for a 2 axle steering. Funny when one tries to do something one tends to over engineer it .. but you have managed to make it so simple :) May I ask if you have a link to those steering boxes ? I see you are running SCX10 axles with what I am assuming are 1.9 wheels. Wondering if the steering boxes will hold up to AR60 axles with 2.2s. Found some Hot Racing steering boxes. Not in the mood of spending $60 for a pair. Wondering what you paid for yours.

Re: Jebster's 10x10 HEMTT rollback hauler
 

Thanks. I am running scx10 axles and 1.9 wheels. The steering boxes are from xtra speed and are intended for Tamiya 1/14 semi. I havent put them through their paces yet but they seem pretty stout. I got mine off eBay for around $13 each.

Re: Jebster's 10x10 HEMTT rollback hauler
 

Thanks for the info :)

Job well done :)

Re: Jebster's 10x10 HEMTT rollback hauler
 

I have been makings progress and will post of pics and a videos soon. In the mean time I have a question for others. I didn't expect a tight turning radius on a rig this long but I wanted to know if running open diffs (vs lockers) in the front two steering axles would improve things noticeably.

Re: Jebster's 10x10 HEMTT rollback hauler
 

Here is a videos of the rollback bed in action. The twin hammers on the back is no lightweight and it does fine.

https://youtu.be/Y92G1fkgL9Q

As you can see in the video the rear axles need heavier duty springs. They are buggy shocks so the springs are soft.

I did have a causality. The output on my GRU snapped off. Trying to decide if I'll buy another unit or fabricate my own. I need a LOT of reduction since the transfer cases I'm running increase the output ratio.

Re: Jebster's 10x10 HEMTT rollback hauler
 

Been working on this body for some time now. Started with someone else design but didn't like allot of it, so doing my own. Think I'm going to make it a go anywhere camper. Like your ideas. Going to use that steering idea in the rear. Started out was going to be 1/16 with WPL axles. Now I've decided to do SCX10 axles, with one set coming from a scrapped AX10 Crawler. Hope you don't mind showing these in your post. The different colors are for me to help distinguish the differ parts.
http://www.rccrawler.com/forum/membe...4548-66757.jpg



http://www.rccrawler.com/forum/membe...4548-66756.jpg





http://www.rccrawler.com/forum/membe...4548-66755.jpg