2 speed tranny w/ 2nd gear as "turbo' ?

[jhautz]

Has anyone tried this? What issues would I run into?

I still run a 2 speed tranny in an Emaxx with a 9920, 9L, 16/66 gearing and 4s Lipo.

When Im running it I find that 1st gear is great power, but is lacking in top end and 2nd gear is a little slugish and has more top end than I use 90% of the time. I can run it all day in 2nd gear and never overheat so I think Im right in the sweet spot as far as 2nd gear goes, but I'd like to gear it down to get a little more punch.

Now my question is....
Can I just gear 1st gear up so that it has the same final gear ratio as 2nd gear if I were to gear it down slightly from where its at now to get more punch. Then... second gear would be geared way to tall for normal driving, but I would be able to use it like a top end turbo boost for the high speed runs. Basically get it up to speed in 1st gear, and then pop it into the tall 2nd gear and see if I can get it up to some ridiculous high speed like 50? 55? or something? Then just for my everyday bashing I'd use first gear 90% of the time like I use 2nd gear now.

So I would have 1st gear as a nice bashing mix between 1st and 2nd now, and 2nd gear not really drivable, but used as a very tall high speed run gear?

Has anyone done this? Would this be hard on the esc even if I only switched to 2nd gear after getting up to speed in 1st gear? I'm thinking as long as I only run 2nd gear startigng at say 25-30mph and up It shouldn't be to bad on the ESC. Any other pitfalls I would expect to see? Thoughts?

I think Im gonna try it this weekend and see what happens.

[JOHNNYMAXXIMA]

Very interesting question. Currious to see what some of the experts have to say.

[BrianG]

Not an "expert", but here goes...

If you were to gear up first gear, I'd go with something a little less than a normal 2nd gear ratio. I wouldn't gear the 2nd speed too high though or you'll load it too much IMO. That would get rid of your sluggishness you have in 2nd also give you a bit more top end.

Current setup:
First gear is a 2.77:1 ratio.
Second gear is a 1.72:1 ratio.
Diffs are 2.85:1 ratio.
66/16 is 4.125:1 ratio.
First gear total ratio = 32:51
Second gear total ratio = 20.22

So, if you are running 66/16 right now and 2nd feels sluggish, I'd say go up to 66/20.

66/20 in first gear = 26:1
66/20 in second gear = 16:17

As you can see, first gear is now somewhere in between your current first and second which should alleviate your sluggish start in second without unloading the motor much, while second gear is now quite a bit higher for that top speed...

[jhautz]

2nd is not slugish, just not as punch as I would like. (i'm used to my 5s, 9xl in my e-revo)

Here is my math. Not an exact match to yours, but close. I did this in a spreadsheet I built for calculating gear ratios/ speed and such. I'm not gonna try and retype what I did Im just attaching a PDF of my speadsheet. This forum will not let me post an Excel preadsheet. To bad. I think its actually kinda nice and simple and would be usfull to thers here. You can change any of the Yellow boxes and the rest of the spreadsheet updates automaticaly in the Excel version.

Anyway. I agree with you. I'm planning on going down a little from the current 2nd gear fianl gear ratio. I wound up at a 66/26 ratio (cuz I have them already) to test this out. I'd probably like to get to a 66/24 for the final setup, but Im gonna test it first before I start buying more $12 5mm pinions, I'm sure it wont get anywhere near the 57mph that I calulated, but It should be interesting anyway.

For some reason I calculated the gear ratios on the emaxx to be:

trans ratio 1st 2.775
trans ratio 2nd 1.63
dif ratio 2.84

Trans/ Diff Ratio 1st 7.88
Trans/ Diff Ratio 2nd 4.63

[BrianG]

66/26...hmm. IMO, I think that's a little high. It's a start anyway, especially if you don't have the other pinions to test. I do know that a couple of teeth can make quite a difference, so I wouldn't trash the idea if 26t doesn't work out for you. If I was a betting man, I'd say your sweet spot will be 20t or 22t for what you're aiming for. I really think any higher and the motor will be overgeared.

As far as calculations, I used my web version, which is similar to yours. I rounded when posting the numbers so that's probably the difference.

[jhautz]

Cool link. Thanks.

Any other issues I should be watching?

ANyone else ever try this tall gearing thing?

If this works on my emaxx I might try it on the eRevo with the 9xl and 5s. According to my calculations, If I could get it run run 66/33 in 2nd gear, theoretical speed would be over 60. I just ordered a 2nd 3s pack as well so I could try 6s on it that way and try for 70. I know.... dreaming... I crash it long before I got there.:p

[BrianG]

I'd just keep an eye on your motor, ESC, and battery temps.

[jhautz]

That goes without saying... I'll let you know what happens w/ the testing this weekend.

[JOHNNYMAXXIMA]

Jhautz,
I am running the same setup that you are (9920/9L but with 14cell NiMh) and I have my gearing at 66/20. Unlike you though, I run 90% of the time in second gear. Temps are great, never had any over heat problems and had it go past the radar gun at 44mph (or 45mph, can't remember).

On my other Maxx, I am running dual 7XL's with gearing at 66/24. The problem that I came across with the 24t pinion is that because of their diameter, they are hitting the motor mount screws (just a little). I had to grind the screws to allow for the clearance. If you are running stock motor mount plate like I am, then I don't think that your 26t is going to fit unless you use some different flatter head screws or something.

[BrianG]

Are there smaller spurs available? Like 60T or something? That would help reduce the diameter and allow the use of more common pinions (16t, 18t, 20t) that you might already have which is the expensive part.

[jhautz]

I used a button head screw on the motor mount. It clears the pinion. The 66/26 is the absolute limit on the stock motor mount. I cant run any bigger without grinding the slots out longer.:024:

I could look at the strobe slipper and the 51T ofna gear. But then Id need to get Mod1 pinions too. I have a 65T spur for the Robinson Racing slipper I use, but its metal and I dont want to chew up pinions. So, 66 is as small as I can find.

I need a radar gun now.....

Lets hope the weather cooperates and lets me test it. I was gonna today but... raining. :035:

[squeeforever]

I actually have 5 brand new Traxxas spurs. There 54T 32P. I think they would work.

[JOHNNYMAXXIMA]

I forgot about those button head screws, I'll have to get me some.
It seemed that the 24t was maxxed out on the slots on mine, not sure if the 26 will fit without some grinding.
Here is the radar gun that I use http://cgi.ebay.com/ws/eBayISAPI.dll...MEWA%3AIT&rd=1 it seems to work really well.
Hey, didn't anyone tell Chicago that it is summer time? Supposed to be 89 degrees where I'm at here in California.:005:

[jhautz]

Originally Posted by squeeforever

I actually have 5 brand new Traxxas spurs. There 54T 32P. I think they would work.

What model are they from? Id like to get my hands on a couple of them. Got a part number I can look up?

[BrianG]

Originally Posted by jhautz

What model are they from? Id like to get my hands on a couple of them. Got a part number I can look up?

Jato? http://www.buytraxxas.com/advanced_s...&keysearch.y=6