Final ratio

[clodbrett]

Anyone done a gear ratio calc on the stock tranny/diff setup? My custom tranny is coming together and I want to figure out how much Improvement I need, and since I sold my tranny, no gear counting for me :(

_bR3T7

[rockspider]

?

Which rig are you talkin' about? X-Factor or Twin Force?

[jimbobmarley]

21:72:1 or something for the TF it is written on the side of the box

[clodbrett]

Yeah, the twin force ratio..

As I received my TF used, I never had a box to look at

And final ratio would be xx.xx:1

So its like .... 2.5:1 for the GD600 X 20:1 (custom tranny) X (ring gear/drive gear)/1


I was just asking if anyone knew how many teeth are on the ring gear, and how many teeth are on the drive gear in the universal.. Pretend its 30/10 then it would be 3.0:1, (its never round)
and then you would go

2.5 x 20 x 3.0 = 150.0:1 final ratio

Of course I have to factor in the 8 tooth pinion somewhere

_bR3T7

[Cubman]

I think he made a typographical error. The ratio printed on the side of my Twin Force box is 27.51:1

The axles have a 13 tooth pinion and 43 tooth ring gear, giving it an approximate ratio of 3.3:1.

That makes the overall ratio 90.783:1 with the stock pinions and spur gear. I do not know how many teeth the stock spur gear has, but if you know that, you can find out the ratio of the stock transmission. 27.51 / (Stock Spur/Stock Pinion) = Stock Transmission ratio.

Hope that helps.
Andrew

[clodbrett]

Thanks cubman, the 13 and 43 number was what I was looking for Yeah, ok, so my tranny is going to be even higher ratio
like, 165:1 or something liek that.

_bR3T7
max rpm on the 55t Integy is like 9200 though, so ..
nice.

[BL_Force]

Originally Posted by Cubman

I think he made a typographical error. The ratio printed on the side of my Twin Force box is 27.51:1

The axles have a 13 tooth pinion and 43 tooth ring gear, giving it an approximate ratio of 3.3:1.

That makes the overall ratio 90.783:1 with the stock pinions and spur gear. I do not know how many teeth the stock spur gear has, but if you know that, you can find out the ratio of the stock transmission. 27.51 / (Stock Spur/Stock Pinion) = Stock Transmission ratio.

Hope that helps.
Andrew

The box is correct. The overall ratio from the motor shaft to the axle in stock configuration is 27.51:1. This number already factors in the axle ratio.

[Robb]

I sat down today, and started doing some ratio comparisons between my pede tranny, and my tf tranny just for curiousity sake. After I did my own gear counting, and measuring turns, to come up with some basic guestimates to work with, I then searched and found this thread, which would have saved a lot of counting.

Then I got very confused because with the numbers I came up with, plus some of the numbers in this thread, I was coming up with a drivetrain (to axle shafts) ratio of around 21-22:1. This was a contradiction to the stated 27.51:1 ratio that had been posted here. Checked my numbers about three times, and just couldn't find what I was missing. Then I pulled out my TF box, and clearly stated on the side of it, is the ratio of 21.71:1. Not sure why my TF seems to be an oddball, but at least my numbers started falling inline.

Out of the box, my TF goes like this:
Stock pinion (18T) to stock spur (50T): ...............2.78:1
Stock spur to DS gear: ........................................2.37:1
Stock axle pinion (13T) to stock ring gear (43T): 3.30:1
Total ratio from motor pinion to axle shafts:.......21.74:1

Now, to that, add in a 3.0:1 GD600, and you end up at 65.23:1 (I will come back to this number soon).

Now, look at a common* pede setup ratio:
Pinion (12T) to spur (84T):................7.0:1
Spur to DS gear:...............................2.72:1
Axle pinion (13T) to axle ring (43T)...3.3:1
Total ratio.........................................62.8 :1

So, the TF out of the box, with an added $20 GD600 + 3.0:1 pinion, creates a very close ratio (65:1 compared to 63:1) to one used by top notch crawlers when using a high turn, low rpm motor.

Brett, why are you going with such a low ratio with a 55t Lathe? Your ratio is more commonly found on high rpm motors. Did a little quick math on your setup, using a generic 6.5" tire:
165:1
55t: 8450 rpm
axle speed (8450/165): 51.21 rpm
6.5” tire (20.4” circumference, ie 20.4” traveled in one rotation)
51.21 rpm x 20.4” = 1045”/minute, or 62,700”/hour, or 1 (.99) mph

This seems really slow. Most 55t users that I have read about, shoot for a ratio in the ballpark of 50-80:1.




*I found this PS (12t/84t) setup to be a popular one in a general discussion of the pede tranny, not vehicle specific to TFs, so this setup may not be the best when used with TF axles

[clodbrett]

Yeah I hear you Robb, I never had a box to look at , so I did like you and counted teeth ;) To be honest, the final ratio of my tranny isn't completed yet. I haven't been able to find the gears I want. My tranny only has three gears in it believe it or not. Its mega simple. Two steped gears with 10-15 t center steps, and hopefully 50-65 tooth lower steps (the big gear on the outside) facing eachother, and the output shafts will be hooked to the middle, so I will have a counter rotational output of those gears, with a GD600 driving the top/side (depending on mounting and CG) with an 8T pinion feeding it. Yeah, and apparently the MAX RPM on the 55t Lathe made by Integy is 9200. So the extra 800ish rpms don't make TOO much difference, but depending on if I can find these step gears the way I want, I should be able to do a top speed of about 5mph

_bR3T7

P.S. I may not need to run the GD if I can get my tranny right. Which would be nice.
Oh, and yes, I flippedand shimmed my front diff to allow for the counter-rotational output ;)

[clodbrett]

Incidentally, the equation for mph is as follows

............(Rpm x Tire Diameter in ")
Mph= _____________________

............(final gearing ratio x 336 )



so I did some counting on my ratios and came up with this :

9200x6.5 = 59,800
65:1 x 336 = 21,840

that is equal to 2.74 mph, which is roughly what I am looking for. That is without the GD600, toss the GD600 on there, and then you have this:

9200 x 6.5 = 59,900
195 x 336 = 65,520

Thats equal to .91 mph top speed ;) a little slow, but torqy I'm sure!!

_bR3T7

[Robb]

I was using the 55T @ 7.2v found in this thread: http://www.rccrawler.com/forum/showt...ght=motor+dyno Guess you are looking to run a higher voltage?


Using your equation works out the same..................I just took the long route.
(8450 * 6.5) / (165 * 336)
54925/55440
.99 mph

[clodbrett]

Math is fun ;)

yeah, I found a thread on here that said the max RPM was 9200 at 7.2 volts.. so who knows now, and as I remember I got flamed for asking too :P hehehe

Either way.. I suppose I could gear for up to a 5mph top speed, my ESC should be able to push the amps at lower RPMS anyway right?

sweet

_bR3T7

[OGmicromonster]

I just put four different Integy 55-turn lathe motors on a cheap dyno. They averaged about 9000 RPM's at 7.2 volts and drew approximately .66 amps. (lowest RPM was about 8920 RPM's and highest was 9120 RPM's) This was under no load. I'll put the motors on a real motor dyno soon and I'll post the numbers (RPM's, Amps, Torque, etc.) here.

I just thought you'd like to know.

[JohnRobHolmes]

shoot for about 60-70:1 final with moab size tires. That puts the crawler at about a walking pace.

[OGmicromonster]

I'm just curious. Where does the 336 come from in the equation? I tried figuring out MPH using that forumula with a known MPH just to compare and I didn't get the same numbers. I may have figured in something wrong, but that's what I'm trying to figure out. The truck I'm building can have a final drive ratio of about 74.81 (this can be changed depending on what gears I use) and will be using a 6.88" dia. tire. I would think figuring out what the roll-out of the truck would be to get an accurate estimate of what the MPH will be is better. Is that right? I'm shooting for a truck that will go approximately 4 MPH with a 55-turn motor (4500 RPM @ 3.6v, or 9000 RPM @ 7.2v - the dyno I used will only run the 55-turn at a lower voltage so I ran it at half the voltage I would be running it). According to the forumula it should be set up like this.

(9000 RPM x 6.88")
-------------------------
(74.81 x 336)


(61,920)
--------------
(25,136.16)


2.46 MPH ???

That's really slow. Can someone double check my math?

[OGmicromonster]

Okay, so I searched the internet and found a PDF that explains the formula to convert final drive gear ratio into MPH. Here is the link. I'll just use that.