Landships II

cwarren64 · Corporal

Renault FT Final Drive Gear Ratio?

Ironsides · Legend

�

Hi Warren I think this may be what your looking for, from this manual...

http://po2260.perso.sfr.fr/FT17/Manuel%20du%20FT/MANUEL-FT17-v0.htm

Cheers wink

�

-- Edited by Ironsides on Wednesday 14th of March 2012 10:24:05 AM

Ironsides · Legend

Hi TinCan Tadpole, Well thats a good question as my French is awfull but as far as I can see the tabel represents gear ratios�for the drive and gearbox with a final ratio expressed as a single figure ie 1st gear�=114.5, �which I assume means a final reduction of 114.5 to 1...

I think the table refers to the number of teeth on each cog/sprocket engaged with the first speed gear being 50 teeth -�16 teeth etc, �I think the secound column representing a set of bevel gears used to change direction, the final three columns�a fixed reduction gearbox (see plate 8, No147 representing the 12 tooth sprocket in the fixed 58-12 combination)

I hope that makes some kind of sense

�

Cheers smile

-- Edited by Ironsides on Wednesday 14th of March 2012 02:39:58 PM

TinCanTadpole · Legend

Are you sure, Ironsides? To me it doesn't look like any comprehensible way to express gear ratios, and even if it is, you'd still have to calculate (approximately at that) the final drive ratio by using the top gear ratio, the most accurate info you can get on engine rpm and top speed, plus the sprocket circumference.

TinCanTadpole · Legend

Okay, that makes some sense. Without completely thinking through whether or not it was correct, I multiplied my way through the table and got:

1st - 114.62
2nd - 56.42
3rd - 34.52
4th - 22.365

From these near figures I take it I worked it out correctly, the differences probably due to rounding in the calculations by whoever came up with the original figures (the fraction button on a modern calculator makes these things more accurate).

Therefore I reach a figure of 26.49 for the 'demultiplicateur', which if you are right, Ironsides, makes a final drive ratio of 26.49:1.

To check this out, that would mean dividing engine rpm by fourth gear ratio (with final drive included) to get sprocket rpm.

Unfortunately I'm not sure of the engine rpm, but I have an idea I've read it recently ("somewhere"!) to be about 1400 or 1450rpm, so I'll try that:

1400�22.365=62.6rpm.

For an approximate sprocket size, I measured the plan on the FT article on Landships 2 (the one with the scale along the bottom). I measured about 34mm diameter on my screen, against a nice round two inches for 1m on the scale; that makes about 67cm for the sprocket diameter, if the plan is drawn accurately, and 62.6rpm of a 67cm sprocket means roughly 2.2metres per second velocity. 2.2m/s equates to 7.92km/h or 4.9mph, which is about right.

So the final drive ratio looks to be 26.49:1

-- Edited by TinCanTadpole on Wednesday 14th of March 2012 10:23:45 PM

Ironsides · Legend

Hi TincanTadpole, the manual has a table for selected gear vs rpm, at 1500rpm in forth gear�= 7.78 kph so close enough I think.

Cheers smile

cwarren64 · Corporal

Thanks guys for the great discussion and information!� This is exactly what I was looking for.� The drive sprocket is actually 66CM so your calculations were pretty much right on target!

Thanks again!

Warren