New Cubmobiles for Pack 505

Show off photos of your cubmobiles, starting ramp and race course.
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rdlongsc
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New Cubmobiles for Pack 505

Post by rdlongsc » Sun Aug 23, 2009 10:18 pm

Pack 505 built 6 new cars over the summer to use in the Battlefield District Cubmobile Race that was held on August 22, 2009. The pictures are posted here: http://s244.photobucket.com/albums/gg24 ... Cubmobile/

The cars are upgraded versions of the old "Battlefield design". You can see the old design cars under the 2008 Battlefield Race results post. They have a improved brake design that has the handle vertical when not being applied instead of tilted forward ~45 degrees. The brake handle is made of two pices of 3/4" plywood laminated together instead of being made from 2x pine studs. This new handle design has a spring that keeps the brake from ever dragging until intentionally applied and a longer braking surface. The brake requires only about 20 degrees of movement to be applied. The brake is centered in the car floor to prevent it from turning the car and is positioned closer to the seat to make it easy for the Scout to grab without leaning forward. The longer handle increases leverage also.

The cars also have a higher back to protect the Scouts in case they hit something and flip (we have seen this when one car runs under another). The axle was mounted above the floor instead of below to lower the CG and minimize the chance of something getting under the car..

The cars were all built using the the Comtech 10 inch wheels and used the factory bearings. I bought a set of Boca Bearings and tested them against the Comtech-supplied bearings. The Bocas were smoother, but not faster. I removed the rubber seals from the Comtech bearings, removed the grease and lubed with oil instead. I pulled the dust shields from the Bocas and repeated the process. When both bearing types were installed in a Comtech wheel, both wheels would freespin over a minute, but the Comtech-supplied bearing wheel would spin about 10 seconds longer than the Boca bearing wheel. I was surprised, but am not one to ignore test results. We went with the Comtech bearings.

In the end, the results could not have been better. We carried 10 scouts to the District race. Only one Scout had every run in a Derby race before. The P505 racers won 9 of 11 available trophies with these new cars. No P505 Scout was beaten by a non-505 Scout in any heat unless they ran out of bounds and could not finish the heat. In the final standings, our Scouts were again not beaten by another pack's drivers.

These cars cost just under $130 each, including hardware, wheels and paint. The plywood is 3/4" cabinet grade birch plywood. The 2 x 4 and 2 x 2 pieces were cut from high quality quarter-sawn 2 x 12x 12 boards to minimize warping and have knot-free structural members. I picked though several lumber stacks to choose boards with dense grain and no knots. You could build these cars using pine sheathing plywood and ordinary pine studs for about $40 less. I will post some close-up pictures of completed car details this week.

RDLONGSC



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sporty
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Re: New Cubmobiles for Pack 505

Post by sporty » Tue Aug 25, 2009 1:01 pm

Those are some nice cubmobiles !

I see some smiles also on the kids faces. looked like it was a fun and great time.


How did the comtech wheels do against the other wheels ?

hard for wider treaded wheels to compete against a ligther/thinner tread wheel.

only way is if the bearings did not get a good prep.

did any of them take the seals off the bearings and remove all the grease ?

Sporty



rdlongsc
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Re: New Cubmobiles for Pack 505

Post by rdlongsc » Tue Aug 25, 2009 9:25 pm

No cars had Comtech wheels except ours, so Comtech's were undefeated also. One car (my son's) had the Comtech rubber seals pulled, the grease removed and bearings lubed with oil. This was the fastest car by about 0.1 sec ( P505 cars were 10.5 to 10.8 seconds over a 150 ft track if the driver went straight.) The cars from other packs with steel wheels ran 11.5 to 12.8 seconds if the driver didn't bobble going down the track.



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