Project BMP

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It begins

Hard to believe it's been two years since my first Project Money Pit entry and 7 years since I first got into the sport.  Over the course of that project I took my short wheelbase Samurai from a leaf sprung off-road machine to a tubed out 4 linked crawler.  I have learned a lot about what works and what doesn't and have been feeling the itch to take the next step and build a crawler from scratch.  One of the important lessons is also the reason for this projects ominous name.  This hobby can be expensive and it never seems to let up, hence the addition of "bottomless" to the project name was natural. 

Making a Plan 

First off this won't be a fast project.  My plan is to have it drivable by winter 2005.  I am hoping I can approach this project in a stepped manner, building it from the drive train up.  I guess this is a good time to list the goals of Project BMP.

1.  Seating for 2 adults and 1 child.

2.  The target weight is 2500 lbs loaded if I stay with a Zuk drivetrain,

2700 lbs. loaded if I go with a Toyota drivetrain.

3.  More storage room than Project MP.

4.  More robust tubing in commonly impacted areas.

5.  Longer wheelbase.  105-109" ?

6.  Better visibility.

Basically I am looking for a recreational crawler that will seat three but still feel light and nimble.  Eventually I'd like to add rear steer which means swapping in a drivetrain that can handle D60's would be good to do during the build up in anticipation of the bigger axles down the road.

Chassis: Utilizing what I have learned over the past few years I plan on making a frame from scratch. 

Axles:  For now, I plan to utilize my existing axles.  They have served me well and I haven't seen the need to change them out. I would like to implement some sort of rear steer down the road as funds permit.

Drive train:  I am still up in the air on this one.  On one hand I have a lightweight and dependable drive train in Project MP but I feel I am pushing the limits of what the stock Samurai transfer case can take.  With bigger axles an inevitable upgrade, this might be a good time to beef up the drive train and get that step out of the way.  The most logical step is to install a Toyota transmission and dual transfer cases.  This would allow me to retain my existing motor which would be good for the budget.  However, now is a good time to do a motor upgrade too.  It will all boil down to what kind of deals I come across in the next couple of months as I search for possible parts cars. 

Suspension:  Links all around.  My existing rear suspension will make its way over from Project MP.  The front will be link with coilovers.    Ensuring adequate clearance between the motor, links, coilovers and steering gear will be one of the harder parts of this project.

The Design

The tubing on Project MP was eventually mocked up in Solidworks so I could see what it would look like before I started building it.  Project BMP will go to the next step and actually use the model as the blueprint.  The goal here is to model everything possible so I will know where and how everything will mount before I start bending tubing.  Another benefit to modeling the buggy before I build it is the ability to get some useful data from the software.  Based on the materials I assign to the parts I can get the weight of the entire vehicle and the center of mass at any time during the design process.    

These images are the result of a couple weekends and many weeknights of work. The design utilizes my existing Beard seats and a smaller version for the rear.

Currently I have 90% of the buggy modeled including a full tank of gas (8 gallon fuel cell), a full cooler (40lbs), two storage bins, battery, Suzuki drivetrain, and hi-lift (mounted behind the seats).  The present weight is right around 2400 lbs.  When I am done with the design I will do a complete break down of the weights.

Some isometric views.  As you can see I have a narrow front end and 90 degree approach angles front and rear.  The tires shown are 37" tall and the wheelbase is at 107".

Here's a comparison with the Project MP model.  I should note the Project MP cage height is not accurate, it should be taller.  In fact, the overall height of Project BMP is roughly 2 inches shorter than Project MP.

Somehow I managed to package all that in a chassis that is only slightly longer than the Project MP chassis.

The main structure of Project BMP consists of a lot of different sized tubing.  Here's the key for the above pictures:

Red = 1.62 Dia x .250 Wall

Blue = 1.62 Dia x .120 Wall

Green = 1.00 Dia x .120 Wall

Orange = 1.00 Dia x .095 Wall

Grey = 1.37 Dia x .120 Wall

Black = 1.50 Dia X .120 Wall

The heavy wall tubing shown in red will be used in the areas my present rig has taken a lot of hits on.  These positions are pretty much the areas most rigs end up pivoting around or take the brunt of the force when rolling.  I am mainly after dent resistance in these areas, from my experience .120 wall is too easy to dent.  Any 1" dia tubing used for bracing is .120 wall, the .095 wall stuff is used for the cooler mount and dash.  I am going to go with 1.37 x .120 wall on any brace that should only see compression or tension loads (no anticipated side impacts).  This was done to offset the increased weight in the .250 tubes.  The 1.50 x .120 wall tubes are used in any brace that may see a side impact.  The other reason for using the slightly smaller diameter 1.50" tubing is so when I mount body panels they will be slightly recessed below the neighboring 1.62 dia tubing.  You may notice I used 1.37 dia tubing  for the door braces which may see a side impact.  I plan on having a small nerf bar on the side like my present rig that will stick out a ways past the door bars.  This serves as a step when getting into the rig and also takes the brunt of the hits when pivoting around something with the side and on hard flops.  My present door braces are unscathed so I am going to continue using what has worked for me.

Note - I have made the plans I used to build this chassis available for purchase, details here.

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