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Discussion Starter #1
I just wanted to cross-post to a thread on RDC that I started yesterday. I thought some of you might be interested in this project.
 

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Discussion Starter #3
Did you click the link and read the thread on RDC? I just updated it this morning.
 

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Nice project....its seems a bit "go fast" specialized to me....so why not go all out in the direction.

Run the power train in the rear mid engine style, bell housing right at the back of the cab. Then run transmission and transfer case in the in between the seats. Center the front diff with very long a-arms in front ( with no engine to work around ). In the rear either do a center rear diff behind the engine with a simple long swingarm suspension like a sand car, or an offset diff solid axle. Use high pinion diffs that are flipped to solve the backwards motor issue. I would use a true hi9 diff front and rear if it was me. It should oil just about like a regular 9" when flipped, plus it would keep the pinions low to help tuck the diff under the engine.

I have always wanted to build a go fast sand/desert car like this. I am a Solidworks designer also and have the full meal deal package at home. I will keep an eye on your project.
 

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Nice project....its seems a bit "go fast" specialized to me....so why not go all out in the direction.

Run the power train in the rear mid engine style, bell housing right at the back of the cab. Then run transmission and transfer case in the in between the seats. Center the front diff with very long a-arms in front ( with no engine to work around ). In the rear either do a center rear diff behind the engine with a simple long swingarm suspension like a sand car, or an offset diff solid axle. Use high pinion diffs that are flipped to solve the backwards motor issue. I would use a true hi9 diff front and rear if it was me. It should oil just about like a regular 9" when flipped, plus it would keep the pinions low to help tuck the diff under the engine.

I have always wanted to build a go fast sand/desert car like this. I am a Solidworks designer also and have the full meal deal package at home. I will keep an eye on your project.
This is pretty much what I have been thinking about building for a while, off set rear diff with a flipped 9" and hummer front portals IFS.
 

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Discussion Starter #6 (Edited)
Nice project....its seems a bit "go fast" specialized to me....so why not go all out in the direction.
Thanks. All of our projects tend to be right on one side or the other of that line between trail rigs and desert trucks. The big fork in the road seems to be whether they've got a straight-axle or IFS. I'm curious to know what else makes this project seem so 'go-fast specialized'. It would be pretty easy to build a straight-axled version of the same basic vehicle, but I think we all have a pretty good idea of how that would perform in the rocks and the desert already.

Run the power train in the rear mid engine style, bell housing right at the back of the cab. Then run transmission and transfer case in the in between the seats. Center the front diff with very long a-arms in front ( with no engine to work around ). In the rear either do a center rear diff behind the engine with a simple long swingarm suspension like a sand car, or an offset diff solid axle. Use high pinion diffs that are flipped to solve the backwards motor issue. I would use a true hi9 diff front and rear if it was me. It should oil just about like a regular 9" when flipped, plus it would keep the pinions low to help tuck the diff under the engine.
Right now I'm thinking that this will be front-engined, but it would be pretty easy to adapt this chassis design to a rear-engined configuration and to run the rear output from the transfercase to a centered front diff, then run the front out put to a slightly offset rear diff. Would obviously need to flips the differentials upside down, which might cause some oiling problems.
I was thinking EXACTLY the same thing (I pulled that quote from the RDC thread). Mounting the drivetrain backwards (rear-engine) is a compromise, like anything else though and I'm not sure which would be better in this case.

It would make packaging the front drivetrain and front suspension components a lot easier and we could use longer A-arms. It would also make rear-mounting the radiator a lot simpler. We'd also be able to push the cab a little bit further forward, which would be good for visibility.

On the other hand, I think we'd have a hard time figuring out where to put the fuel cell and I'd like to be able to carry at least 30 gallons (40 would be better). It would also be quite a bit more expensive to build because people would have to run flipped diffs and an offset rear axle.

I think weight distribution is a wash, and a front-mounted engine might even be a little better in my opinion. Have you ever noticed how all the rear-engine buggies tend to look nose-heavy when they jump, while the front-engine trucks fly nose-high. I know I'm making a generalization, but it seems to hold true for the most part.

I have always wanted to build a go fast sand/desert car like this. I am a Solidworks designer also and have the full meal deal package at home. I will keep an eye on your project.
Well it's not just my project, so I hope you'll do more than keep an eye on it. I'd really like to get everyone's input and help along the way if you have anything to offer. Hell, I'm hoping that someone will BUILD one of these things before I do. It's going to be at least a year or two before I'm ready to tear down my Tacoma because I just rolled it out of the shop under it's own power a few months ago for the first time in about two years.
 

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Discussion Starter #7
This is pretty much what I have been thinking about building for a while, off set rear diff with a flipped 9" and hummer front portals IFS.
Yeah, someone esle suggested that on the RDC thread and Brad Falin's Hummer-based Class 1 car is one of my favorites...

What do you guys think? I guess the engine location is really the first thing we need to decide on.
 

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Discussion Starter #8
I sent an email to Brad Falin today and I'm hoping to be able to ask him a few questions about the Hummer components he used to build his Class 1 car. I'm not sure how I feel about designing the front suspension around Hummer portals.

The first thing we need to decide is where to put the engine. I just made a post on RDC, listing all the Pros/Cons that I could think of. Please take a look and let me know what you guys think.
 

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I sent an email to Brad Falin today and I'm hoping to be able to ask him a few questions about the Hummer components he used to build his Class 1 car. I'm not sure how I feel about designing the front suspension around Hummer portals.

The first thing we need to decide is where to put the engine. I just made a post on RDC, listing all the Pros/Cons that I could think of. Please take a look and let me know what you guys think.
I saw that car before and was trying to figure out who they were the other day when I was t thinking about this.
 

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I had half way gone with this idea, then decided to just go full hydraulic.
Industrial planetaries move the gears and planetaries all the way through the wheel so the input can be closer to the center line of the bearing which should also be the center line of the wheel. This type can allow for closer mounting of the CV to the centerline of the wheel. Planetaries can differ alot on there speed input and output. Mine are rated at 5000 RPM input and 167 RPM output 30:1 reduction. With a 48" tire this will get you 23 MPH. If you take one apart and see the gear and bearing arangement, you can see that they can go way faster. Most are setup to accept Hyd motor which are splined, but they can be modified to accept CVs if you add bearigns. With the right ratio these can become an option. Take a fast 200MPH, high 300+ HP IFS, say Subaru rally car, run a fast input speed into 4:1 ratio planetaries, then you can get moving at 50MPH, actually faster after tire size increase.
If your going IFS then might as well go IRS. Four of the same spindles and hubs and two of the same diffs. I do realize that it is not as easy as I have put it, Thats why I went the slow route.
Also think about the unsprung weight of planetaries, they will not be fun to control going fast.
 

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Discussion Starter #12
Thanks for the input. I've seen your project and it looks like you're doing a great job building something really unique. Please don't take this the wrong way, but I just want to build something that I know will WORK. Trying to make a 4WD IFS vehicle that's actually trail-worthy is about as big a challenge as I think I'm up to right now. So I'm going to stick with conventional drivetrain components wherever possible. IRS would open up a whole 'nother can of worms that I really don't feel like dealing with. I'd really prefer to keep it simple and go with what's been proven to work (straight axle with a triangulated 4-link).
 

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So are you trying to build a trail rig or desert rig?

First thing to do is the suspension, get your points setup then build your chassis around them. I'd run a mid engine for desert, but don't know for a trail rig. Front or rear engine can be made to have whatever weight distrabution you want, suspension design and shock tuning can also have a big part in how straight the truck flies. Usually the more rear biased the weight is the straighter it flies.

The chassis has way too many tubes imo. Do be done right you should really run some sort of analysis on it (FEM) and it should help you trim it down to what you need. Also for the dimensions I would use a vehicle you know were you fit and have someone measure were your head is at, etc. Then I would add 6" to that all the way aorund for your head, same with arms/legs, etc. Arms and legs I don't think I would use the 6" As if you are in a sistuation those parts will push in, the head doesn't. Also make use of different sized tubing, non contact members use a thinker wall, etc.

I don't know much about portals or Hummer portals but from what I have seen they don't seem to be very durable, desert running with them would worry me.

Something I want to try but have not seen yet is the use of a fuel bladder rather then a traditonal cell. That way you can place it were you want and low to keep the CG down. I think Ralley cars use bladders.
 

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Discussion Starter #14
I know what you're saying about starting with the suspension design, but I knew that would be affected by the drivetrain layout so I started by looking at how I could package things around a front or rear-mounted engine. I'm not sure that I agree with you about "the more rear biased the weight is the straighter it flies" but I'm leaning towards a front-mounted engine after sorting through all the pros and cons (there's a list on the RDC thread).

The things that's are steering me away from the Hummer portals are the inboard brakes and all the braking force going through the CV's, the unsprung weight, and the kinppin inclination / scrub radius, although it might be possible to run wheels with a lot of backspacing to help with that. I'm just not sure if the little bit of additional ground clearance is worth all that.
 

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We have played with different weight distributions and thats what we have found. We also have seen the effects of it with different teams and different comps. We run rear engines in our stuff and the cars typically with 70%+ rear weight fly perfect, One of the teams was notorious for running that much rear weight, this year their car was somewhere under 60% rear and it didn't fly nearly as straight.

Suspension can also play into how it flys. If it's swept back it will tend to nose dive more as the suspension will not pop the front as much compared to a suspension that has to move in an arc or even vertically. It's much more then were your engine is sitting.

As for what to start with, personally I would rather make drive train compromises then suspension.
 

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Discussion Starter #16
What kind of vehicles? Rock crawlers? Rock Racers? Desert racers? I understand that there are more variables than just engine location, it's just one of the things I was considering when trying to decide whether to put the engine in the front or the rear of this vehicle.

By the way, this is the list I was referring to:

JESSE_at_TLT (from RDC) said:
I was originally planning to make this vehicle with a rear-mounted engine, then I changed my mind and decided to 'keep it simple'. But I spent some more time over the weekend making a list of pros & cons and now I don't know which way I want to go.

Help me figure out where to put this engine.


Rear-mounted engine: Advantages

A rear-mounted engine would allow us to run a center-mounted front differential (longer CV's) and we'd have a lot more freedom to design the front suspension components without the engine in the way.

We'd also be able to run a spine (boxed sheetmetal backbone) all the way from the front differential through the back of the cab, to the 4-link mounting points like Dump suggested. That would make for a pretty strong, lightweight chassis and if we integrated the front suspension mounting points into the spine, it would also make the whole thing a lot easier to fabricate.

This drivetrain layout would lend itself to a cab-forward design and without an engine up front, the occupants would have great visibility.

Makes the decision to run a rear-mounted radiator a no-brainer.

Rear-mounted engine: Disadvantages

A rear-mounted engine would drive the front differential with the rear output from the transfer-case, and the rear differential with the front output from the transfer-case. This would require the differentials to be flipped upside down in order to make them rotate in the right direction. The guys over on the Pirate forum seem to have figured out how to get oil to the pinion bearing on a flipped Ford 9", but flipped differentials would be drive the coast-side of the gears, effectively running in reverse. I don't know if that would even be an issue on a vehicle like this, but using True Hi 9 differentials could solve that problem (at least in the rear where it's most likely to be an issue). A rear-mounted engine would also require the use of an offset differential at the rear axle. I'm not sure if the additional complication (flipped differentials) and expense (custom rear axle assembly) is really a disadvantage when it's all said and done, but it is something to consider.

Picturing how everything would be packaged in a 4WD chassis with a rear-mounted engine, I'm not sure where we'd be able to put the fuel cell. I think this vehicle needs to hold at least 30 gallons of fuel (40 would be better) and I know a lot of people say it really doesn't seem to really matter, but I like the idea of trying to keep the fuel-mass as centralized as possible. It's impossible to say now, but I'm guesing that a custom fuel cell will have to be designed and made specifically for this chassis. That's another big expense compared to buying an off-the-shelf fuel cell.

With respect to weight distribution (front vs. rear engine), I'm not sure whether a rear-mounted engine is an advantage or a disadvantage. The rear-engine buggies look nose-heavy when they jump, while the front-engine trucks fly nose-high. Seems backwards, but I've read a lot of discussions on here about it and I remember someone making the comparison to paper-airplanes and weighting the nose with a paperclip to get them to fly further/straighter. I'm not interested in building a 'jumping truck', but that is one aspect of an off-road vehicle's handling performance. What about other handling characteristics?
 

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Discussion Starter #17
Getting back into this project. Check out the thread on RDC for updates. Could use some input regarding component selection so we can acquire parts and start designing the suspension.
 

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I just started a new thread on RDC, asking for feedback on the lower links for the rear suspension that I've designed. Would appreciate input from any of you guys over here too. Follow the link and there are images and CAD files to download. I'll continue to update this thread with all of the general stuff related to this project.

 

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My rear links are made verysimilar to that, they are made of DOM and 3/16 HR steel. They have bent, you need more material across the top, those will buckle at the shock mouting points. I would run a long shock rod end and a wider top plate that goes around the shock pockets, make the sides taper up to the top.

I have been thinking more and more about building this type of procket, came across 2 sets of hummer portals cheap.
 

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Discussion Starter #20
Thanks Drew. That kind of feedback is really helpful. I'd like to avoid using longer lower rod ends if at all possible because the packaging is working really well right now. The upper shock mounts tie-in right behind the shoulder-height crossbar at the B-pillar. It's just really compact and clean. Obviously, I'll use them if we need to, but I'd like to see if I can work around the shock bodies first.

Brad was supposed to ship me all those Hummer parts today so I can start modeling them. You were pretty set on using a rear-mounted engine, right? I decided to go with a front/mid-mounted engine so we'll have some useable bed-space behind the cab. I'll upload some screen-shots of where the chassis is at right now.
 
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