Tamiya Vajra Built and Finished

I actually built the Vajra in early 2012 but didn't finish the body until early 2013.  The build was a good one and quite interesting, but not without some frustration at the design in some places.  I understand why Tamiya made the choices they did, I think, but I still feel like a better design for these parts I am about to mention could have been thought of for the Avante chassis (on which the Vajra is based).  I realize the basic design of the chassis is over 25 years old and fault can be found in almost all chassis designs, but for some reason some of the design "issues" I found during the build of the Vajra jumped out at me as very obvious and annoying from an engineering perspective.  Maybe I was in a hyper-critical mood during the build or something.

For the first one, in step 10 of the manual, a piece of tape is used to hold a gear shaft on the front end before a front suspension arm is mounted that blocks the shaft from coming out.  

Tape?  Really?

All Tamiya had to do was put a flat-headed screw right next to the shaft to hold it in place, similar to how suspension arm hinge pins are held in place on some modern buggies.  The shaft diameter is very thin at 2mm, too, compared to the normal 5mm Tamiya normally uses.  This, to me, seems like a design failure because compromises were made that undermine the reliability of the vehicle or at least raise serious questions about it.  Again, I think I know why they designed it that way: First, they had to allow the bevel gear (H2) to be removed quickly because it prevents the removal of the diff and they didn't want you to have to take the gearbox halves apart to do it.  Second, the 2mm shaft diameter was chosen due to the limited amount of space and bevel gear design inside the front gearbox.  Anything larger would not have fit.  But take a look at the TA-01 design, which has similar driveshaft-to-front-diff mechanics but doesn't have tape holding a 2mm shaft in place.  Sure, it has one more gear in between the bevel and diff, but seems to be a stronger design.  In my opinion, too many compromises were made in order to eliminate one gear "for improved efficiency".

Another frustration is that the front and rear outer diff joints are only held in place by the pressure of the swing shaft dogbones and the foam/springs inside their cups pushing against them.  There is no screw holding them in place, so when a dogbone is removed, the diff joint falls out.

BA25 and BA26 are only held in place by the dogbones inserted into them

No big deal, right?  I mean, other Tamiya kits have diff joints that aren't held in place either.  That's true, but at least those diff joints have a much longer shaft profile that sticks inside the differential unit itself like the ones that come with the stock Avante 2011 re-release shown here:

PB10 and PB11 fit deep inside the differential and don't fall out easily

The Vajra outer diff joints have very short interlocking protrusions that mate with the differential inner joints and they wobble as they spin under load making the whole system seem unreliable.  I am also concerned that the outer diff joints are going to wear out quickly.  Yet it's almost impossible to buy them separately.  TamiyaUSA's store is perpetually out-of-stock, not to mention how expensive they are.  After all of this complaining, I should note that I have not had the diff joints pop out at any time during many battery packs of driving.  As for wear, the jury is still out.

The wheels and tires.  Taken from the brushless powered Tamiya Super Levant (57796), I think the wheels and tires are simply too heavy for this chassis.  They make the Vajra seem clumsy.  The chassis, which is nothing more than a lengthened Avante chassis reminiscent of the Egress, wasn't designed for large truck tires.  Installing regular buggy wheels and tires, however, transforms the Vajra into a pretty nice truck.  

The adjustable turnbuckles, while having tiny hex nuts built into them which make adjustments somewhat tedious, are handy for making the necessary camber and toe-in modifications.

I know many people do not like the styling of the body, but I actually don't mind it so I won't count it as another negative talking point.  What I did do, however, was cut the front wheel wells narrower than marked in the manual since I knew from the start that I'd be using smaller wheels and tires.  The black lines in the below picture approximate the curves I followed.  Check out the pictures below of the finished body on the chassis to see the front wheel well cut outs in more detail.

Black lines show approximate front wheel cut outs I made

I highly recommend replacing the stock servo saver with the hi-torque one from Tamiya (51000).  It eliminates some slop associated with the stock servo saver making the truck more responsive.

Here are some pictures of the finished chassis with a few different types of wheels and tires mounted.

Stock wheels and tires:

Duratrax wheels and Duratrax Bandito tires:

Seben Racing BRF3 wheels and tires:

The truck uses a Futaba R113ip receiver, Futaba MC330CR electronic speed control and Hitec HS-645MG servo for steering.  The motor is an unknown brand unlabeled 19 turn double wind. 

The body was simple to paint because it was all one color: black.  I used Tamiya PS-5 Black (86005) after masking the windows.  The manual calls for Tamiya PS-31 Smoke (86031) to tint the windows but I left them clear.


Here are more pictures showing the wheel and tire combinations with the body.  If you look closely at the side decals in the pictures and compare them with the decal sheet, you'll notice that the "Vajra" text has been removed.  I strategically removed the text from the decals because I am not very fond of the name.  Due to the decal's busy lightning bolt style design, it's hard to tell the text is missing unless you know where to look.