Alvin

GEAR THAT MOTOR!
Here are the recommended rollout ratios for the following motors winds:

ROAR Stock 30.99 to 34.38
17 turn 31.08 to 31.86
16 turn 29.47 to 30.30
15 turn 27.86 to 28.68
14 turn 27.08
13 turn 26.28
12 turn 25.53
11 turn 24.69
10 turn 23.88
9 turn 23.10

How to compute for rollout?

Rollout = (tire height x Pi) / final drive

tire height = 63-64mm (measure that sucker with a caliper!)
Pi = 3.14159
final drive = (spur gear / pinion) reduction ratio
reduction ratio = specified in r/c manual (i.e. 2.25 for HPI Pro3)

How to use this Table?

Generally, if you stay within the recommended roll out range that is specified in the above table, you should have adequate speed and performance from your motor.

Note that the range for stock motor is the widest and therefore the most difficult to gear. This takes into account that different stock motors are built for different performance parameters. If your stock motor is for speed (i.e. green machine based motors), you should gear it at the lower end of the range. If it is for torque (i.e. P2K2 based motors) you should gear it at the higher end of the range. Mid range motors with both speed and torque like the Reedy MVP are to be geared in the mid part of the range. Be aware that the these recommendations are merely starting points for gearing and may still be fine tuned.

Modified motors have very little or almost no range in their recommended rollout. Gearing for performance is then much more critical to avoid over or under gearing. Take note that both under and over gearing cause motor burn out and overheating! The recommended ratio is a good starting point and should be increased as you use a motor with more winds (i.e. plus 0.4 points for single, double and so on). A 10 turn quint should be geared more like a 9 turn single than a 10 turn single!

I personally have found great success in tuning my Chrome Stock motor from Orion by gearing it at the high end of the range. Without this guide, I would have thrown out that Orion Top based can a long time ago. Now, I'm actually thinking of buying one again as I have been able to make it perform well!

NOTE: roll out takes into account the differences between car kits! a motor can be transferred from one car to another with no change in the rollout as long as the running weight is approximately the same.

Jack

hmm
MS...
let see
TC had his gear at about 9.1 for his low turn mod...
baggy had his at 8.8 for his 10 turn
i had mine for 8.5 with 11 turn...
8.15 sound okie.. if you cant make the 5 min mark then try 8.5 or so...

fReShJiVe

ok ill try that...thanks jack

Jack

Alvin, maybe when u are free, come and join us at MS..
Eguy and noel is pretty good with the rollout...
you could check with them.

Alvin

Jack: Not I don't wanna go to HB track, it's just too far away, and public transport is seemingly non-existent

Jack

take MRT then take Bus
i always do that..

Alvin

Still no thanks. I tried that twice, leave my place about 730 in the morning reach the track already 9 plus plus. Bleh. And it is so much more grimy than rc speedway.

Alvin

This is a shot of my comm. After just 4 packs of running. The springs included were 135degrees. I just got a pack of 150 degree Orion springs, will try them out.

Jack

hmmm
that is a goner...
i dont think it your spring that did all the work...
your brushes and your gearing together ..
Jurong track is consider techincal u know.. so it pretty hard on the com if u gear it so low

Alvin

One reason I don't think it is overgeared is because last I overgeared a 14x2 @ 5.5:1 FDR (115/45). The motor came back _HOT_. The plastic bulkheads were HOT! And I still used it for 2 races ;-)

The 13x2 on all 4 packs came back *warm* after a fully dumped GP 3000 pack. I could hold my thumb there, no probs. Even a Tamiya Type T after 5 minutes is hotter than this 13x2.

I'm not trashing it yet, and I'm sure the gearing is correct - it tops out just as I turn in from the straight - and it is definitely slower than Ozone's 11x3 geared @ 8:1 FDR.

One more thing. For the Race and Practises before, it was geared at 7.6:1 FDR, which is rather low when you compare to the ppl gearing their 11 turns @ 8... and still the brushes KO'd after 4 packs. 3 packs, on practice day

Jack

seriously speaking Alvin, i think u are crazy to gear Mod motor at 5.51 .. it like for STOCK motor.. hehehhe
maybe you got a shot motor...

sigh.,.. it hard to explain to you...you cant really compare 11 turn motor with 13 turn motor
diff power band

fReShJiVe

i was running a ratio of 8.15 and 8.625 with Kawada V-Mod 11X2...and the motor was hot....really hot...can't even touch it for more than 3sec.Any suggestion on what i should gear it at??my comm was also slightly burnt but not like the one Alvin posted(that's roasted ) as i'm not sure which ratio made the comm burnt maybe i'll try running 8.625 again and check it....by the way does using a short brush leads to this??mine is quite short but the spring is still pushing the brush!!
oh by the way how long does the brush last...mine has become really short after about 12packs
arghh !!maybe i'll just get a better mod motor...any suggestion to this and how much and where to buy it

dw

If your motor is reaching maximum write at the end of the straight then you are overgeared. Motor should reach maximum 2/3 to 3/4 of the way down the straight.

That motor is toast though. Changing from 135 to 150 degree springs will not make that much difference.
The only time I have seen a comm that bad was when somebody I know polished the comm with metal polish and didn't get it off properly before using the motor.
I think their is probably something else wrong apart from gearing / springs. Unless you are running in very hot ambient conditions.

Did the motor ever run right?

Once a motor has got that hot it will never run as good against. Heating the copper up affects the conductivity.

freshjive:
Short brush = less spring tension = more arcing = hotter motor
Brushes depending on type should last 2 - 15 runs.
If the motor overheats all the lubricant in the brush will burn off so they must be replaced.

Alvin

dw: Thanks! Looks like I gotta search for a new motor
Nope. The very first time I ran it, it was with a 7.6:1 FDR, I ran about 3 packs with it before it crapped out. The state of the comm was exactly like the one pictured above. I thought it was because my motor was undergeared (topping out at about 1/2 way through the straight).

So basically your gearing recommendation is to hit top speed about 2/3 to 3/4 down the straight right? Mmm I'll give the motor one last shot with the new brushes I got today, else I'm gonna use the can and stick my 23T arms in ;-)

Thanks again dw.

~Alvin

fReShJiVe

dw,
thank for the reply ....by the way does having a tight gear mesh make the motor burnt???i was just looking at my car and notice that the gear mesh seems tight...could it be??maybe the motor need to work harder to get it move as it's tight...am i correct??
hmm!!long way for me to go to learn all this rc stuffs ....seems to cant get anything right at the moment ....maybe i should go back to nitro