Brushless gearing starting point

[uniquenamehere]

Hey all, I've got the following setup:

- 3300kv Reedy brushless,
- Brushless Hobbies LT4,
- 7.4v 5000 mah 40c,
- 2.25 stealth,
- 72 tooth spur gear.

I'm pretty green with brushless... can anyone recommend a pinion gear as a starting point for me?

[dldiaz]

If my math is correct:
(72/19) x 2.25 = 8.5

So, a 19 tooth pinion will give you a Final Drive Ratio of 8.5.
That's probably a safe place to start - just check motor temps frequently at first to be sure it's not overheating.

[Coelacanth]

Speaking about final drive ratios, is there an "optimal range" that's regardless of the make/model of car? For example, the Optima Mid's internal gear ratio is ~ 2.64, so with a spur/pinion ratio of 85/18, the F.D.R. would be rather high at 12.47. I can always get a higher-tooth pinion but all I have in 48-pitch is a 16T and 18T. I can't down-size the spur much either as the pinion won't reach it to mesh properly.

Ahh the subject of gearing...not many people really get into the mathematics behind it but it's so important, for understanding effects on performance & overheating protection of motor & ESC!

[RC104ever]

Well, I think I have a Castle 5700 kv motor, 81 tooth spur and I think a 21 or 22 pinion (can't remember) and the thing literally screams on 2S lipo. I can't imagine it with anything faster quite frankly. It was even good with a 4600 kv but I think its just about perfect now. Hoping to try it on a track sometime soon so I can actually see how it handles, now that I know the straight line speed is not an issue.

[dldiaz]

Speaking about final drive ratios, is there an "optimal range" that's regardless of the make/model of car?

I guess it's kinda hard to describe a range for any/all models because things like the weight of the model, number of driven wheels, drivetrain friction, tire size, and running environment/terrain all influence the "optimum ratio".

That's not even to mention the differences between all the motors/esc's/batteries...
Even two 14-turn motors (or two 17.5 brushless, whatever) can have quite different heat/rpm ranges, thus requiring different gear ratios...

Considering 1/10 2wd buggies (RC10 and JRX-2), I generally end up in the 6.5 to 9.5 range for Final Drive Ratio.

EDIT: I suppose a 4wd like an Optima would require a numerically higher ratio (maybe 8 to 12), in order to overcome the extra traction/friction and get all 4 wheels spinning.

[uniquenamehere]

Okay... I'll start with a 19T, and maybe buy a few extras +/- a tooth or two.

Just out of curiosity, where do you guys get your pinion gears?

[Coelacanth]

Just out of curiosity, where do you guys get your pinion gears?

I'd be interested to know too, I need to pick up 3 or 4, some in 32-pitch and some in 48-pitch. There's lots of sellers on eBay selling the gears for 5 bucks each plus shipping...maybe someone would want to do a "pinion gear exchange"?

[DMAT]

hot racing has a good bit of gear.

rw racing has a lot too but communication is slow.

[kaiser]

http://teamnovak.com/tech_info/view_article/26

this chart from novak is where i go when just starting out with gearing, go up or down from the suggested starting point.

this chart has never let me down.

print it an put a copy in your box.

[SoAzRC]

That Novak chart is the same I use with no problems. I like the oval numbers for rollout too. Just throws the tire size into the equation.

[uniquenamehere]

http://teamnovak.com/tech_info/view_article/26

this chart from novak is where i go when just starting out with gearing, go up or down from the suggested starting point.

this chart has never let me down.

print it an put a copy in your box.

That looks pretty handy. Too bad they don't list KV instead of turns... I have no idea how many turns the Reedy 300kv motor is.

[kaiser]

CLOSE TO A 13.5

[kink]

Is there are very basic method to convert some of these suggestions into brushed 19T ballpark ideas?

[kaiser]

NO, there are too many variables with brushed, single, double, triple, quad winds. brush style, timing. it's been so longs since i ran any brushed motors hotter then 27turns.

[dldiaz]

Is there are very basic method to convert some of these suggestions into brushed 19T ballpark ideas?

I run several brushed motors, including a few 19-turn (Trinity Chameleon, Reedy Quad Mag) - I find the higher end of the range I mentioned above (for RC10 and JRX-2) to work well for these motors.

In other words, a Final Drive Ratio of 8:1 or 9:1, works pretty well for a race-spec 19 turn motor - I don't like to run 'em very hot... depending on your heat tolerance, you could push those numbers lower.