Gearing help

Hi,

Could anyone give me pointers on how to increase the gear ratio beyond what the smallest available motor pinion permits? I'm looking to convert an Ofna buggy and would really like to try get 15:1 final ratio. Apparently one can install a larger spur gear or use smaller bevel gears in the front and rear diffs. However, I can't find any specific information about what size spur and bevel gears are available that will fit Ofna diffs.

Can anyone offer me some pointers please?


Thanks,
Aragon

[Serum]

What ofna buggy is this about?

most Ofna buggies use a steel spur, which can be replaced by a 51T plastic one.

if the diffs are 43/13 (3.308:1 ratio) If you used a 51T spur and a 12T pinion, you have got an end ratio of 1:14. I would not use a 10T pinion, they tend to wear fast.

It is the Jammin X1-CR. Yes, front and rear diffs are 43/13.

Is the 51T spur a drop-in replacement for the stock 48T Ofna spur? Is that spur an Ofna part?

I ordered the buggy today. Can't wait to get it! :)

[Serum]

No, the 51T spur would need an adapter, it's not a bolt-on for the X1-CR IIRC, it's using a steel spur, which covers the entire centerdiff.. something the 51t spur doesn't.

Why are you hammered on that gearing? do you need to buy a BL motor or do you have got one already?

[nieles]

i am not 100% positive but i think this will fit
http://www.rc-monster.com/proddetail...YOIF148&cat=40

than you need a 10 tooth pinion to archive the 15:1 ratio

[Serum]

Yeah, true Niels, it most likely would. But it would not give hime the 15:1 ratio he is looking for.

I want to run 8S. I need to decide between a 1512/2Y or 1912/1Y. I do not know which yet as I still need to see how much space and gearing I have to work with in the buggy.

Upsides of the 1512 are that it's easier to seal and is 2 ounces lighter. Upsides of the 1912 are that gearing options are easy due to lower Kv.

I would like to be able to gear my car for top speeds of 40 mph or less (even though I will probably experiment with faster too).

From specs I've read, 1:8 tires are approx 5 inches diameter.

Open to 8S suggestions though. :) I have not purchased any of the power system components yet.

No one ever run 8S in a buggy?

[Sedri]

Aragon, I have no idea what end result you are after -

I set up an MP 7.5 with 43/13 diffs, 44/16 center gearing, and a 540XL 6T on 4S, and the buggy was just ridiculously fast and nearly uncontrollable; how in the world would 8S work? I was actually thinking of "tuning down" power a little by switching to a 9T 540L with 4S.

On 8S, I don't know how your motor would ever see anything close to the ideal of full throttle...!

At first I was geared for a top speed of 45 mph with 14/46 center gearing, and the motor ran hot from being notoriously undergeared, and full throttle was simply impossible without looping out and crashing. Simply not enough traction with that kind of torque/hp in a 7 1/2 pound chassis.

[jollyjumper]

stuff the hotbodies pro diffs in your car.
(43/10)x(46/13)=15.21

Originally Posted by Sedri

Aragon, I have no idea what end result you are after

I am after maximum efficiency.

Originally Posted by Sedri

I set up an MP 7.5 with 43/13 diffs, 44/16 center gearing, and a 540XL 6T on 4S, and the buggy was just ridiculously fast and nearly uncontrollable; how in the world would 8S work? I was actually thinking of "tuning down" power a little by switching to a 9T 540L with 4S.

Your experience sounds correct. Both the setups you describe would have been capable of over 50 mph by my calculation...

Originally Posted by Sedri

On 8S, I don't know how your motor would ever see anything close to the ideal of full throttle...!

Yup, this is why I want to gear down to a controllable speed, but...

Originally Posted by Sedri

At first I was geared for a top speed of 45 mph with 14/46 center gearing, and the motor ran hot from being notoriously undergeared,

...maybe I have more to learn. That's interesting. Is this a common problem with all brushless systems? Is there anyway to calculate if this will occur with a setup before running it?

Originally Posted by Sedri

and full throttle was simply impossible without looping out and crashing. Simply not enough traction with that kind of torque/hp in a 7 1/2 pound chassis.

That I hope to work around ala MGM's programmable soft start. Is my thinking correct?

Originally Posted by jollyjumper

stuff the hotbodies pro diffs in your car.
(43/10)x(46/13)=15.21

Thanks. Will check 'em out. :)

[jollyjumper]

glad to help. good luck with your X1.

[nieles]

Originally Posted by Aragon

I am after maximum efficiency.

get a neu or a lehner

Yea, I'm after a Neu. Either a 1512/2Y or 1912/1Y depending on gearing and mounting options...