Gravity Vehicle C

iwonder
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Re: Gravity Vehicle C

Postby iwonder » March 20th, 2013, 9:27 am

Oh, not quite... The extended inner race means that the inner ring on the bearing is wider than the rest of the bearing, it's not a matter of surface area. I use shaft collars on my axles to keep them in line, so this way the shaft collar isn't running along the outer race of the bearing, causing drag.

Edit: I forgot to mention... My bearings aren't in the wheels, they're separate, I think that's where your confusion came from Joey.

And balsaman, I see how smaller inner diameters are better, but smaller outer diameters as well? Surely not by much...
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Re: Gravity Vehicle C

Postby joeyjoejoe » March 20th, 2013, 9:46 am

Oh, I see, you probably tighten nuts or fix allen collars (you call them shaft collars) on either side of the bearing to fix it to the threaded axle then. Your wheels are also fixed to the axle. Is that right?

You also mention that your bearings were rated ABEC 3 which provided tight tolerences. I know this is probably going to open up a can of worms, but how does the ABEC rating do this? I have a collection of bearings going from ABEC 1 to ABEC 9 and I honestly don't see a performance difference between any of them.
Last edited by joeyjoejoe on March 20th, 2013, 9:52 am, edited 2 times in total.

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Re: Gravity Vehicle C

Postby mrsteven » March 20th, 2013, 9:49 am

What were some of the best scores in your division?
You should really specify a distance when asking about scoring
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Re: Gravity Vehicle C

Postby Balsa Man » March 20th, 2013, 9:59 am

Smaller (inner and outer diameter, and hence ball size) gets you less friction simply because of less contact area. Big amount, no, not at all, but whatever the difference is, it's multiplied by 4, and it affects velocity throughout the run.

A better way to assess than ABEC rating is a running torque spec. Many of the bearing manufacturer's web sites have tech specs providing initial and rolling torque.
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Re: Gravity Vehicle C

Postby Mgras46 » March 20th, 2013, 10:06 am

Gravity vehicle 7.5 meters

iwonder
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Re: Gravity Vehicle C

Postby iwonder » March 20th, 2013, 11:45 am

ABEC differences aren't really noted till you start loading the bearings way down and possibly trying to do lead screws for high tolerance machine tools.

Also, I use a solid axle, not a threaded one ;)
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Re: Gravity Vehicle C

Postby catfoot » March 20th, 2013, 7:44 pm

I am so using those $3 bearings from now on.

Also, how did you apply the CA glue to secure the axle(s) to your bearings? What I was doing was putting glue around the axle and then sliding the axle back and forth to distribute glue onto the bearings, then positioning it properly and leaving it to dry. This process, however, did not seem to yield fantastic results and I would definitely like to learn a new one.

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Re: Gravity Vehicle C

Postby mrsteven » March 20th, 2013, 7:53 pm

I am so using those $3 bearings from now on.

Also, how did you apply the CA glue to secure the axle(s) to your bearings? What I was doing was putting glue around the axle and then sliding the axle back and forth to distribute glue onto the bearings, then positioning it properly and leaving it to dry. This process, however, did not seem to yield fantastic results and I would definitely like to learn a new one.
If you found the bearings I used (3.14 in price I think? I seem to remember something about pi....) they work great.
I place the axle where it should go, tape on either side of the bearing on the axle so there is a slot between them, glue in that area between the tape and slide it back on. DONT use too much glue or it will drip into the bearing. And spin the axle slowly while it dries so the glue is even and doesnt have a chance to leak out of the opening. It also helps to center the axle in the bearing if it doesnt have a tight fit. This is what I did...

a real option is to not even glue them at all, I mean seriously. The axle will always choose the lowest friction way to spin so give it the option of the bearing or slide in the inner race. Unless there is a reason to set the axle in permanently, dont. My back axle with the breaks is glued in because it is important it doesnt slide side-to-side, but the front axle isnt because that doesnt matter, there is no force on the axle outside of rotation to make it WANT to slide side-to-side.
If you're going to glue, I would recommend CA glue, straight glue not the rubberized stuff. I tested with rubberized CA, CA, JB weld and a couple other less known glues. I found that the CA glue joint from rod to bearing was the strongest. I was able to hammer off the bearings with all the other glues in a few good hits. With the CA glue joint, I hit it maaany times and even then the bearing actually gave out and broke before the CA did. I tested after using the rubberized CA and it didnt work and forced me to rebuild my car -_-
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Re: Gravity Vehicle C

Postby _HenryHscioly_ » March 24th, 2013, 12:14 am

Is an open sight that's 74cm long attached to the ramp more precise than lining the ramp up with the start line, or is it more accurate but less precise?
and is there any reason to make it signficantly shorter than 75cm other than transportation?

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Re: Gravity Vehicle C

Postby _HenryHscioly_ » April 7th, 2013, 5:41 pm

SoCal; 8.1m
I started re-testing my vehicle from regionals, theday before state....spent all my time building boomi
I decided not to attach my scope..
I couldn't tell how the start line was made..but it was on school gym floor, and no 90degree tools were in sight.
First run was 0-1mm longitude, 7cm left. maybe if I didnt trust their start line and used a scope system, the first run could have improved
Second run, I adjusted very poorly...and it was still about 7.2cm left, .5cm to far ahead
I knew I could have done much better on my second run... so I just prayed for a medal(6thplace)..
In the end, up 7th, which is not bad :]
I heard that some people got 0cm...like, 1mm, and a couple 2cm
I guess it was pretty competitive :)


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