Archive for December, 2010

Bearings in Spur Gear Assembly

Thursday, December 23rd, 2010

One of the critical performance (and often overlooked) issues in modern RC touring cars is bearing drag.  When most RC industry companies design RC cars, they design the plastic parts without regard for plastic shrinkage.  When plastics cool after injection molding, the plastic parts tend to shrink slightly.

For example, if a company designs an 8mm hole to fit an 8mm bearing, the hole will actually be smaller than 8mm.  It won’t be a lot smaller, but it will be small enough that it will press too much on the bearing and cause the bearing to drag internally.  For example, the AE spur gear assembly was clearly designed for 8mm bearings but the holes are actually only 7.97mm.  If the bearings are simply forced into the undersized hole, the bearings will not spin as freely as they should because the plastic is actually slightly crushing the outside of the bearings.

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Bad Bulkhead

Tuesday, December 14th, 2010

I just realized that one of the screw holes in one of my bulkheads won’t hold a screw.  The hole was drilled too big before it was tapped, so the threads are barely there.  The screw falls back out easily.  I need to stop building and contact Associated.

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Suspension – Make sure it does not bind

Tuesday, December 14th, 2010

When assembling the suspension, it is possible that the arms will bind when you tighten the screw to mount the suspension arms to the bulkheads.  You need to take special care to avoid this problem.

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Suspension Arms and Pins

Tuesday, December 14th, 2010

You need to double check the suspension arm holes and suspension pins to make sure they do not bind.  If they do bind, your car will not handle consistently.

The first step is to run a reamer through the suspension arm holes to make sure the holes are straight and the proper sized.  For this step, I decided to use a tool from Hudy.  When using this Hudy tool, be sure to rotate the reamer slowly while sliding the tool in and out of the holes.  This will remove any extra plastic that could cause binding without removing too much material.

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CVD/CVA Building Tips

Tuesday, December 14th, 2010

The CVD axles are often overlooked as a place to invest some additional time sanding and polishing.  If you build your CVD using the instructions from the kit, the CVD will work fine, but you will be leaving some performance on the table.  A little fine sanding with 2000 grit sand paper can reduce the friction in the CVD joints, which can result in a faster car.

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CVD – Wrong Size Hole in Part

Sunday, December 12th, 2010

One of the CVD axels that came with my kit has the wrong size hole drilled into it.  I am stopping my build to contact Associated about it.  Here are some pictures.

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Diff Building Tip

Sunday, December 12th, 2010

When building the differentials in the car, it is important to scuff the surface of the diff rings with 600 grit sand paper.  This will make it easier for the diff balls to grab.  You will be able to run the diff looser without it slipping.

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Shock Building Tips

Sunday, December 12th, 2010

The first step is to take all of the shock components out of their bags and organize them carefully on the table.  I typically group like parts together at this point to make it easier to inspect the parts.

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Chassis Preparation

Friday, December 10th, 2010

A lot of people race their cars without doing any special prep work to the carbon fiber chassis.  You can do the same if you are in a hurry, but I encourage you to spend some time on the chassis.

I like to carefully sand, glue, and re-sand the edge of each carbon fiber part (chassis, shock towers, upper deck, etc).  By doing these steps, the chassis and other carbon fiber parts are less likely to crack during a wreck.  Additionally, the carbon fiber parts will look a lot better when properly prepared, which is awesome when you are busy bench racing.
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