Wheel bearings or not

[cubdad]

My question is weather or not bearings are the way to go. Seems to me that if you have a good setup and lite wheels ie RSXs bearings would not make that much of a difference. Bearings by nature are for load bearing but the actual load of a derby car is not that great. Also they would add weight to the wheel and thus slow acceleration on take off. Am I way off base here. I have no experience with bearings to base this on, just speculation.

[jetmugg]

I am pondering the same question. My daughter's GS pack is going to have a Powder-Puff derby, and will also have a semi-outlaw parent's race. For the parent's race, we have to use the same dimensions and weight as the "stock" rules, but other than that, anything goes. I am thinking of using a 3/32" straight-through rear axle with ball bearings and custom machined Nylon wheels (I manage a machine shop as part of my day job". I would then use another 3/32" stub axle on the dominant front side, set up with some positive camber and angled towards the rail. The 4th wheel would be a dummy, just for show.

I'm thinking that this setup might be easier to build and tune (perhaps requiring less expertise with alignment and testing than a needle axle setup). I might be way off base, but I'm willing to sink a few bucks and some time into finding out.

That is, unless the experts say something like - Don't waste your time with ball bearings, they will make your car slower.

SteveM.

[Lucky 13]

If set up correctly, ball bearings are the way to go. Checkout www.derbymonkeygarage.com to see the newest bearing wheels on the market from Goat Boy Racing and Derby Worx. Bearing wheels are expensive, but in the right hands, are faster than needle axles and wheels.

Jetmugg...it sounds like you are on your way to a nice set up !!


Lucky 13

[jetmugg]

I'm working on the setup today, and will have a first-run tomorrow morning. I'm hoping to pull a little "suprise" victory in the Renegade class at our Cub Scout derby.

It looks like derbymonkeygarage.com is not in service.

[psycaz]

derbymonkeygarage.com is back online.

[jetmugg]

Just an FYI - I ran my ball bearing equipped "Renegade" car this afternoon at our Troop's PWD. My car set a new track record, and totally smoked the rest of the outlaw field. I don't know the actual length of the track, but I know that my overall time for 4 runs was 9.036 seconds, with an average scale speed of 266 mph.

I was running ABEC 7 bearings, 3/32" ID and 3/16"OD, on custom CNC-ed nylon wheels, 0.042" thick. Drill rod was used for the axles, 1 pc axle in the rear, with a cambered and toe-ed in dominant front wheel.

These things are seriously fast.

[cycrunner]

Jetmugg,
How did you secure the axel to the bearing - press fit, loose or bonded with adhesive?

[andylester]

Jan 23, 2010 16:27:56 GMT -6 jetmugg said:

Just an FYI - I ran my ball bearing equipped "Renegade" car this afternoon at our Troop's PWD. My car set a new track record, and totally smoked the rest of the outlaw field. I don't know the actual length of the track, but I know that my overall time for 4 runs was 9.036 seconds, with an average scale speed of 266 mph.

I was running ABEC 7 bearings, 3/32" ID and 3/16"OD, on custom CNC-ed nylon wheels, 0.042" thick. Drill rod was used for the axles, 1 pc axle in the rear, with a cambered and toe-ed in dominant front wheel.

These things are seriously fast.

That sounds awesome on the bearing car! ;D

Over at the PWD Racing League, we have a growing class for racing bearing cars. You should send it in and get in on the fun! It is kind of a new class, and we are all still learning what works and what does not, so I bet your car would fit right in.

www.pwdracingleague.com

Stop by the forum and check out the rules for the Extreme Pro Mod class and send you car in for some good old proxy racing fun. ;D

[jetmugg]

The bearings were a "press" fit onto the axles. The bearings were spec'ed for a 0.0937 +0, - 0.0002" shaft. The shaft was spec'ed as 0.0937 +/- 0.0003". As received, the shaft was too tight to get into the bearings. I chucked the shaft in a drill and worked it with 600 grit paper until it was a rather snug press fit (by hand) into the bearings. These bearings seem pretty delicate, so I wanted a good fit without having to stress the bearings.

I'll look into sending this car for a proxy race. It's really nothing special, more of a learning experience with the bearings, wheels, and assembly techniques. I'll have to post a pic or two.

SteveM.

[nmanhipot]

jetmugg,

Assuming 266 mph at 1/25th scale, you're actual speed was 10.6 mph or 15.6 fps. Given that your average speed was 2.259 seconds, you're looking at 35.25 feet of racing distance.

What were some of the other times on this track? Can you describe the track? Aluminum? 4' drop?

I'd send this car in for sure. Sounds awesome. Got a picture of the car and/or the track?

[jetmugg]

I think it's a Best Track, but I'm not 100% on that. Aluminum, 4 lanes, probably about a 4' drop, with a pre-fabbed curve section and a raised rubber rail as a braking section. I don't know how the timing was triggered, but there was a "red eye" type of setup several inches in front of the gate.

The next-fastest car had razor-thin wheels, washers on the axles, and was built by a guy who works as a mechanic in a high-end motorcycle shop. It was a very sharp car, and the guy definitely did not expect to get beat. Over the 4 races, I beat him by almost 0.400 seconds total.

I'll have to load up some pics.

SteveM

[jetmugg]

After looking at some website pics, I'm pretty sure it was a Best Track, 4 lane, 35 foot length. They were using a Fasttrack timing setup.

[jetmugg]

Let me see if I can post a couple of photos....

[jetmugg]

The photos are not too great. I'll try to take some better pics. Knowing what I do now, my next attempt will be a lower profile car, and I will do more of the hole drilling and alignment work before shaping the body of the car.

I still haven't figured out the exact running length and overall length of the track that was used. In general, are the timers started by the dropping gate, or by the individual cars.? I ask because our track had a single red-eye, garage door type beam shooting across all 4 lanes, set up in front (down hill) from the actual starting pins. At the finish line, the timing detectors were set up in the vertical direction.

SteveM.

[nmanhipot]

I'm no expert, but I think you've got a very fast car there. I'd seriously consider sending that bad boy in for a proxy race or two. We know from your time and given speed that the calculated distance was 35.25'.

We have a 35' Best Track but our timing system bases our average speeds on the actual running distance of ~28'. Your average speed may be a tad high, but your average time is certainly fast at 2.259". IF you were on our track, your average speed might be somewhere in the neighborhood of 217 miles, unless, of course, you were actually on a 42' track. Let us know.

Here's Best Track's website: www.besttrack.com/

[jetmugg]

I'm gathering some boxes (1 inside another) and packing foam to send my car to a proxy race. I don't think that my car is likely to be as fast as the numbers that were generated at our pack's derby. Something doesn't seem quite right with the times and length of the track.

When a company like Best Track lists a 35' track, is that measured from the starting pin, or from the very back edge of the track (behind where the cars start)

Anyway, I think I'll send the car in for a proxy race to get a fair comparison and establish baseline time and relative speed #'s.

SteveM.

[jetmugg]

Let me see if I can post a couple of photos of the track.....

[jetmugg]

The more I look at the pics, I think the track is a 35' length (5 sections of 7 feet each). I'll guess that the actual running distance of the track is somewhere between 32 and 33 feet. I assume that in the timing software, there has to be a field for track length. If 35' were entered in that field, even though the actual running length of the track is only 32.5 feet or so, then the calculated speeds would be artificially high, which seems entirely plausible.

If I assume an average 2.259 second time over a 32.5' distance, then the average velocity works out to 14.38 fps, which seems to be more in-line with what some others are reporting.

In any event, I need to get my car packed up and shipped out for the Feb. proxy race.

SteveM.

[nmanhipot]

We've got the same track - a 35' BestTrack but with a different timer, the Champ, whereas yours' is (edit: FastTrack) . We're also using their new software which gave us a racing distance of 29' exactly. I measured the average times and speeds for four cars' heats to determine this. The 2.259 seconds over 29' is 12.84 fps (rounded) for an equivalent speed of 218.8 mph. I haven't been able to get specifications online for the BestTracks, but this is a very fast equivalent time.

Good luck in the proxy race and let us know which one you do and how it goes!

[nmanhipot]

Now I'm wondering if maybe our timing system's programmed distance is off or not. Hmmm.