Project BMP

Page 3


Virtual Fabrication

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The parts truck is going fast and most of it has been parted out over the last week.  During this time I finalized the drive train for Project BMP.  I will use the existing 1.6 16v motor and mate it to the Toyota G52 transmission with an SOS Ringr adapter.  The power will then go to a pair of Toyota transfer case mated with an adapter from Marlin Crawler.  The front case will stay stock with a 2.28:1 low range ratio and the rear case will have a 4.7:1 ratio.

The chart above shows the gear ratios this combination will give me.  You may remember I was planning on using the 22r that came in the parts truck.  A couple things led me to this decision.  The first involved the hunt for fuel injection parts for the 22r.  I told myself if I could find the parts cheaply and easily enough I would go that route.  I thought for sure I had accomplished these goals when a generous Arizonan offered me a free 22re from an 82 Celica.  I picked up the car but later learned the 82-83 Celica's used an older analog EFI system.  I may have been able to make it work but I wasn't really wanting to get sidetracked on a project of that magnitude, especially since I had a perfectly good, low mileage EFI motor sitting in the garage.  My 1.6 should do the job and the decrease in chassis weight vs. my old chassis should help.  The Ringr transmission adapter also allows me to run the 1.6 16v flywheel which is much heavier than the Samurai flywheel I am running right now.  This extra mass should make the 1.6 feel more luggable at low rpms. 

I got quite a bit of design work done last weekend.  The front link geometry is done with all four links having roughly 30 degrees of triangulation between each other. This design will eliminate the need for a panhard bar which will evenly distribute the forces the links will see locating the axle side to side amongst 8 mounts instead of just the 2 panhard mounting points.

One great benefit of modeling my crawler is the ability move components around and see what effect it has on the center of gravity (CG) of the rig.  Obviously lower is better.  You may notice my weight has jumped up.  I discovered a bug with the way Solidworks handles mirrored parts.  Basically the material properties of the mirrored parts were not automatically carried over from the parent part, this resulted in the mirrored parts weighing about a tenth of what they should have.  I had to go back thru the model and verify each part had the right properties, the mistake cost me about 250lbs.

I ended up lowering the gas tank and rear cooler mount  4 inches by building a floor that hangs down below the main frame rails.  This also allowed me to mount the storage box and CO2 bottle lower in the chassis.  The battery was then moved from high in the engine bay to the floor behind the passenger seat.  These changes lowered the CG of the crawler just over 1.25 inches.  Every little bit helps. 

Now is probably a good time to point out some basic shop safety.  Always chock the vehicle before working under it.  As you can see my assistant Bob got a little careless.  Thankfully Bob is pretty flexible (being a sponge and all) and he was able to walk it off.

The floors will utilize clear lexan in an effort to increase visibility.

One of the last remaining tasks is to locate the sway bar.  You can see here I modeled it in 3 positions to check for clearance, at rest and 30 degrees in either direction.  From the looks of it I will end up with it attached to the rear axle.  The front end is pretty limited on space and I think the sway bar would hit my hydro lines.  A longer sway bar would work up front but I'd like to utilize my existing bar.  In order for it to work in the rear I will have shift the storage box and CO2 tank forward and up an inch.

Update 7-28-04

Just like fabricating in real life, the project starts out with lots of visual progress early on but slows towards the end as the details are worked out.  The cooler rack/rear seat/sway bar/fuel cell mounting took some time to figure out since it was all interrelated.  I have it setup so the sway bar can swing up beside the fuel cell without interference and the fuel cell is still removable by pulling the rear seat.  You may also notice the rock lights are mounted as well.  I have found that mounting the lights away from high shock areas keeps the bulbs alive longer.  The challenge is getting light to the front and nerf bar areas without mounting lights near those high impact zones.

I modeled some light beams to get an idea of where the light would fall.  This setup illuminates the area beside the rig and both front tires, a setup I really loved when my Zuk had sheet metal.

Up front the winch mounting is nailed down as are the radiator and fairlead mounts (the teeth are to scare small children). 

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