What gear ratio should I go with?

[XZIVR]

Okay, something happened to my stock SRC gen III Pro gears in my V3 gearbox. The small gear on the bevel gear is free spinning on the shaft. No idea wtf happened there, but I'm just going to get a new gearset.

Since it seems to run perfectly fine on the stock gear ratio, I figured I would just count it out and buy the same thing. This is where the trouble starts.

I superglued the shaft back in so I could turn the gears in place and count out the ratio. So what I found is the bevel gear turns 8.75 times per one rotation of the sector gear. On all my other guns, it's more like 14-16.. So what the hell? I made sure nothing else was slipping and re-checked my count like 10 times but I get the same result each time. I therefore have no clue what I should do now. as far as what ratio to buy..


My motor is a G&P M120 and it's pulling a M120 spring for a ~420 FPS setup per local field limits. Running on a 1500mah 11.1 20C lipo.

I also don't understand the different way some gear ratios are stated. For example 14:1 AFAIK is rotations of the bevel gear to rotations of the sector gear. What is it when it's like 72:1? Or 100:200?

Any help much appreciated..

[HKGhost]

The gear ratio works from the pinion gear to the sector gear. So "72:1" = 72 pinion gear turns to 1 sector gear turn. Those 200:100 just means it's twice the torque of normal gears (18:1), 300:100 means three times the torque. If you want to pull heavier springs, anything over 20:1 will work fine. The higher the number, the more torque it has. The lower, the faster (Speed gears) the sector gear will be. Hope that helps

[XZIVR]

Okay, so my pinion-bevel gear ratio is 3. So that would mean my current ratio is about 8.75 x 3 = 26.25:1. So the 72:1 ratio is roughly 3 times slower? That just doesn't sound right to me..

[wind_comm]

18:1 is the standard/"original" ratio. (TM's and such)
~13:1 would be speed gears (use a high torque motor. no really, you read that right.)
32:1/72:1/100:200 etc would be torque gears (for pulling stupidly strong springs, wouldn't be legal anywhere in Canada)

then again, maybe I just read ASM too much and think 50+bps @400 fps is normal.

[MaciekA]

Originally Posted by HKGhost

The gear ratio works from the pinion gear to the sector gear. So "72:1" = 72 pinion gear turns to 1 sector gear turn. Those 200:100 just means it's twice the torque of normal gears (18:1), 300:100 means three times the torque. If you want to pull heavier springs, anything over 20:1 will work fine. The higher the number, the more torque it has. The lower, the faster (Speed gears) the sector gear will be. Hope that helps

With 300:100 torque gears, are we able to convert that to a 54:1 ratio? Or am I interpreting this wrong?

Thanks.. This thread is long overdue learning material for me

[MaciekA]

Just an addendum to my question above, to add confusion to the topic, on Airsoft Mechanics there is a thread where the following is claimed

So 200:100 are - 23.79 :1, and 300:100 - 26.43 :1.

I'm not sure how these numbers are supposed to relate to each other.

I will add that I tried out the SHS 300:100 helical gears (after getting them as a "hey you should try these out" replacement for damaged G&P gears), and I love the relaxed RoF and quietness I got from them. I had to spend a lot of extra time and care shimming them to perfection though, as I heard that helicals can get a little hairy if you don't shim them just right.

[XZIVR]

Yeah, I read that too. Flat gears really don't care if they are a little off.

I'm just still surprised they can vary that much. From as low as 13:1 all the way up to 80 something?


Edit: In the meantime I tossed in my Modify Nano Torque gears (22.2:1) and they are actually FASTER than the stock gears. My ROF was like 30 something!

[HKGhost]

When you see 300:100 and 200:100, that is some brand's way of telling you which gear set has more torque. So instead of saying these gears are torque up, high torque and infinite torque, they given you a ratio number. But this isn't what the actual ratio of the gears. Here's a guide that I made to help me figure out the ratio of my gear set. It is very tedious to do, and if not done correctly, you'll get a weird ratio.

[XZIVR]

Right, so for, say, a 300:100 set, how many times will the motor turn for one rotation of the sector gear? That is, what is the actual gear ratio?

[HKGhost]

300:100 is not the actual ratio. Use the guide I made to determined the ratio. If you don't have the gears, just think of 300:100 is triple the torque of 18:1. I'm gonna guess (depending on the manufacture) it's around 28-35:1.

[MaciekA]

HKGhost, thanks so much for this info, I've been trying to hunt down clarification on this issue for a while and you've just completely cleared it up for me.

[XZIVR]

Yeah obviously 300:100 isn't the actual ratio, but I wasn't sure how to equate that to an actual ratio. If its just 3 x the standard 18:1 then fair enough. As an engineering tech I know a thing or two about gears but stating your ratio as a multiple of some other implied ratio seems pants-on-head retarded to me.

[wind_comm]

Originally Posted by XZIVR

but stating your ratio as a multiple of some other implied ratio seems pants-on-head retarded to me.

you pretty much nailed it.

[HKGhost]

I didn't come up with the idea to put 300:100 on gears. If you have a huge problem with that, contact the manufacturers and ask them why they use that. Otherwise, if understanding it better would be using "high torque, double torque or whatever", than look for gear set that state something you'll understand. I just try and keep things simple so anyone can understand it, and can apply it to their needs.

Originally Posted by XZIVR

Yeah obviously 300:100 isn't the actual ratio, but I wasn't sure how to equate that to an actual ratio. If its just 3 x the standard 18:1 then fair enough. As an engineering tech I know a thing or two about gears but stating your ratio as a multiple of some other implied ratio seems pants-on-head retarded to me.

[MaciekA]

The following picture might be of interest to anyone following this thread: