Subject:
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Check my math? 8448 gearbox ratios
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Newsgroups:
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lugnet.technic
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Date:
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Tue, 14 Dec 1999 20:54:04 GMT
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Viewed:
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570 times
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While disassembling my 8448 last night, I decided to
work out the gear ratios from the engine output to
the drive axle. I came up with the following (many
apologies if this has been discussed here before). This
is ascii art, so if you're on the web interface, click
on "view raw message" to see a more sensible diagram.
Top level: Bottom level:
||
[-A1-----][-A2-] || ||
|| [-B1-----][-B2-] || ||
|| || || || ||
|| || || || ||
[-C1---][-C3---][-C5---] [-D1---] ||
|| || || || ||
|| || || || ||
|| || || || ||
|| || || || ||
|| [-C2---][-C4---] || [-E1---]
[-CR---] || || [-D2-------][-E2---]
|| || || || ||
|| || || || ||
A IN B D=OUT E
Gear sizes: Layer connections:
A1 = 20T B1 = 20T D1 = -C1
A2 = 12T B2 = 12T D2 = -2/3 CR
Cx = 16T E1 = -C4
D1 = 16T E1 = 16T
D2 = 24T E2 = 16T
All Cx's spin freely on their axles; only one may be
engaged onto A, IN, or B.
The math:
1st gear: C1 = A = -3/5 IN 4th gear: C4 = B = -5/3 IN
C3 = -C1 E2 = E1 = -C4
D1 = -C3 D2 = -2/3 E2
OUT = -3/5 IN OUT = -(2/3)(5/3) IN
OUT = -10/9 IN
2nd gear: C2 = IN
C4 = -C2 5th gear: C5 = B = -5/3 IN
E2 = E1 = -C4 C3 = -C5
D2 = -2/3 E2 D1 = -C3
OUT = -2/3 IN OUT = -5/3 IN
3rd gear: C3 = IN Reverse: CR = A = -3/5 IN
OUT = D1 = -C3 D2 = -2/3 CR
OUT = -IN OUT = 2/5 IN
Gearbox ratios (to nearest 0.001):
vs. IN vs. 1st
1st = -0.6 1.0
2nd = -0.667 1.111
3rd = -1.0 1.667
4th = -1.111 1.852
5th = -1.667 2.778
Reverse = 0.4 -0.667
The jump from 4th to 5th seems a little steep to
me, but I don't immediately see how it could be
improved. I also like how reverse is in fact
slower than first.
-Tim
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Message has 1 Reply:
 | | Re: Check my math? 8448 gearbox ratios
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| Tim, I also worked out the gearbox ratios after I built my 8448 and got the same results. I must admit your diagrams are a lot neater than mine! Actually, I did my analysis all the way to the rear axle, which turns 1.5 times slower than the drive (...) (25 years ago, 27-Dec-99, to lugnet.technic)
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