Project BMP

Page 29

   
 
 

Testing

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It figures as soon as I get my rig ready to go we get hit by the summer monsoons.  It was 103 at 51% humidity when I took these pictures outside.  According to the weather people there are some good storms heading north towards Phoenix which would put them over us about the time I planned to head out to test out the new axles.  Unless the storms miraculously break up it looks like testing will have to wait for another week.  Since I am watching the little guy this weekend there isn't much to report project wise.  I did do some more cosmetic stuff, the biggest project was painting some flames on the side of the rig.

First I started with a large piece of white construction paper and cut an angle to match my front body panel lines.  Next I drew the flames on the construction paper and cut them out.  I was left with my template and a piece of paper in the shape of the flames, I taped the paper I cut from the template to the body as shown in the first picture to get an idea of how they would look.  Once I was happy, I took the template and cut some extra rectangular holes in it as shown in the 2nd picture  The extra holes gave me more points to tape the template to the body. I actually added even more rectangular cutouts after I did the drivers side since the force of the aerosol from the spray can caused the template to pull away in some spots.

Here's the finished results.

I measured the outside of tire to outside of tire to be approx 81".

There is 14" of clearance under each differential and just over 21" of clearance under the belly.

Update 6-30-05 - The test run went very well.  I have a few small things to adjust mostly involving the bump stops.  The 42" tires are a squeeze on my chassis which was originally designed for 39's.  Up front I need to move the air filter to clear the tire.

Out back I could actually move the bump stops up a bit and gain some up travel. I also need to come up with a retaining clip to hold the lower coil seat on, I lost one later in the day despite having a set of tender coils which are supposed to maintain downward pressure on the coils when the suspension drops out.

On the trail the buggy exceeded my expectations.  The new tires worked very well and allowed me to walk up a few obstacles I couldn't drive last time.  The suspension also worked very well and I eliminated all of the body roll I had with the previous incarnation.  I didn't move the links too much, mostly some adjustments to accommodate the larger axles.  I feel most of the change came thanks to the larger tires, my suspension now provides very little lift so the link angles are very shallow.  

For future reference here are the theoretical numbers I was aiming for the front (on the left) and rear suspension.  As soon as I replace the coil retainer I lost I take some measurements and post what the numbers ended up being.

Update 8-6-05 - As promised here are the numbers of my suspension plugged into the 4 link calculator spreadsheet as built.  One thing I did notice was the chassis sits lower than I expected it to.  I suspect I forgot to account for moving the upper shock mounting points upward.  Regardless I ended up with a  pretty neutral suspension according to the theoretical numbers.  Based on what I had experienced on the first test drive I think the theoretical numbers are pretty accurate. 

rearaxleupdated.jpg (92231 bytes)

Update 8-24-06 - It has been a year and I finally tried using the adjustment hole on the axle bridge.  this adjustment lowered the rear upper link approximately 1.5".  The change in theory lowers the anti-squat about 30%, lowers the roll center height about 2" and increases the roll axis 2 degrees, After driving several trails I noticed the rig climbs better and the little bit of hop I would experience on really vertical obstacles is gone.  Overall I like the change and was surprised I could notice such a small adjustment.

I also addressed the other issues that came up during the first test drive. To get some clearance between the air filter and front tire I purchased a smaller air filter and then modified the mount to allow me to move the whole filter assembly up a few inches.

 

I also tried driving the buggy around without the swaybar.  The body roll was much less than before but not gone so I decided to keep the swaybar.  I think I could have eliminated the swaybar if I could have moved the lower shock mounts up front farther out on the axle housing.  As it sits right now thy are as far out as I can get them which put them in the exact same spot as my previous axles.  Since I was keeping the swaybar I did have to relocate the lower mounts further inboard to eliminate an interference on the passenger side,

The last thing I did was make some small retaining straps from aluminum to keep the lower coil buckets attached to the shock and to keep the helper coil slider moving with the upper coil.   

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