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Q. about gearing, and some more questions
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Aero
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Question Q. about gearing, and some more questions - 01.01.2011, 01:30 AM

Hi RC monster and happy new year! start with a question is that okey ?

when people write their gearing xx/xx , what does it refer to? mean in rel. to total gearing. assuming rest of gearing is the same ? i'd assume there's gear differences in trucks and 'vehicles'. are diffs in general same gear ratio? so the xx/xx is obviously a hint to more or less gearing, but how to put that into ones individual calc/setup, relate to ir etc. ? when talking motors, isnt it the total gearing that matter, and not some count of whatever teeth ?

I am trying to catch a drift, with the gearing jargon, and believe noone has the same rc, or at least far from everyone. I can see how 'add or lose a tooth on pinion/spur' would make sense in a gearing/motor/battery/esc matter, as it tells the direction (up/down) of gearing change. Just don't get how some pinion/spur count would matter, if its individual in many cases.

as for gearing, how do i find the good range, or the outer limit? is any change in gearing a motor at all, a sure downturn in efficiency ? How to determine for a motor ? as overgearing and undergearing (i prefer to say 'more' and 'less', its making more at-once sense) does stress the motor otherwise off than standard, the temp rise from either going too fast, or going too tough ?

Right, some reading i have done along the sideline here in some years, but hope to be more active here in this year ;) BrianG's calculator is very neat, I need (sorry for rhyming) to figure out what gearing is meant with xx/xx.

im used to metric system, but do know imperial. the usual short numbers alone doesnt always compute. the switch of ',' and '.' is a bugger. if one doesnt know what data it is..32p 48p mod1 or checking diameters mm/" etc.

i would like to get at least one 44mm motor, any good bets on which ones are cheap ? l-cans and more ;) fastened endbells, can-wire-exit, no-ribs, and so on. well i would like some that has interchangeable endbells, if there's some of those ?

mainly want to switch motors from 36mm to 44mm and beyond.
--
If knowing total gearing, weight of truck, and weight of wheels, can a kv-rating be calculated for a given battery voltage. ? Can BrianG maybe comment on this ?

---
and a theor. q. : can you guys comment on POV: 4 x 2s1p 30c vs 1 x 8s1p 30c. goods and bads ? Disregarding wiring resistance and not thermal matters, amps, and runtime. I have this idea that 4 packs are more logic than 1 pack and would like to get low on that one..
---
There must be some where to get 6mm mod1 pinions nearby europe ? do rcm sell this ?
---
can rcm-shop please post high detail images, and specifications of the slipperential ?
   
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E-Revonut
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01.01.2011, 02:51 AM

generally people refer to the gearing as spur/pinion and let you know what the vehicle is. Most regulars can determine the diffs and tranny ratios on here and help you with that info


RC-Monster RC8T 1515 2.5D/MMM/5s RC-M 4500mah
SC10 MMPro 13.5T 2s NeuEnery 5000mah
RC18T Mamba 25/5400kv 2s lipo + 6s NiMh
   
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BrianG
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01.01.2011, 03:49 AM

Usually, XX in XX/YY is the larger gear, while the YY is the smaller gear. So, XX divided by YY gives you a ratio. Example, a 46T spur and 12T pinion would be 46/12, and would equal 3.833:1 ratio. Which just means that the pinion will spin 3.833 times for every revolution of the spur.

By the way, the "spur" could be an actual spur, or the ring gear in a diff.

To get a starting point for gearing, some like to use a 1:1 rollout, which is simply geared such that one revolution of the motor moves the vehicle 1". And then you go from there using motor/ESC/battery temps as a guide. This page helps you calculate the 1:1 rollout: http://scriptasylum.com/rc_speed/rollout_ratio.html

If you don't know where to start in selecting a motor for a particular usage, try this page: http://scriptasylum.com/rc_speed/car_setup.html

This page lets you convert between pitch and modulus for gears: http://scriptasylum.com/rc_speed/gear_calc.html

As far as what motors to get, Castle's Neu-derived motors are a good bet while being relatively inexpensive. There are clones of Castle's motors out there which are cheaper, but they do take shortcuts so their efficiency is not as high. Generally, look for closed endbells (keeps dirt out), finned design (helps cooling), where the wires are NOT extensions of the coils. Some motors like Feigao have wires that are just part of the coils, and don't bend as well as a noodle-wire type of wiring that Castle uses on their motors.

As far as pack wiring (4x 2s1p vs 1x 8s1p), it comes down to vehicle layout and wiring. People use multiple packs in series because the vehicle layout requires it (like the Traxxas E-Revo). Also, you may have a lot of 4s packs for different vehicles, so it makes sense to just use two of them to get 8s instead of buying an 8s pack. Also, using multiple packs adds more wiring/connectors that adds resistance and more places for something to go wrong. Generally, use a single pack where possible.

However, most packs come wired for up to 6s max. Probably because there are very few balancers that handle more than 6s per pack. To get higher cells counts above 6s, just put them in series.
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Dj_Sparky
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01.01.2011, 09:42 PM

http://www.offshoreelectrics.com/pro...eations+Motors

Castle Creations motor sale:

1518 = 60$

1520 = 65$

1717 = 70$

These used to cost around 150-200$, but Castle are clearing them out. These motors weren't sold as combos with an ESC, and that is the reason why they haven't sold as well as 1515 for example, which was sold with an ESC and RTR kits, and is still at a high price.

These are some of the most powerful and most efficient 1/8 motors around. For the price, they are the best. 1717 is good for a heavy vehicle, like a GST 7.7/LST XXL conversion, while 1518/1520's are better for lighter vehicles, for example a truggy like Losi 8ight-T or a MT like the Savage (Not as heavy as the GST/XXL).

The 1717 is slightly larger in diameter, so finding a mount for it will be harder than the "standard" 1518/1520 sizes.

Last edited by Dj_Sparky; 01.01.2011 at 09:44 PM.
   
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lincpimp
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01.01.2011, 10:12 PM

Quote:
Originally Posted by Aero View Post
and a theor. q. : can you guys comment on POV: 4 x 2s1p 30c vs 1 x 8s1p 30c. goods and bads ? Disregarding wiring resistance and not thermal matters, amps, and runtime. I have this idea that 4 packs are more logic than 1 pack and would like to get low on that one..
---
I will say that a 8s1p pack will be superior to using 4 2s1p packs. Generally most of the lipo mfgs use some sort of cell matching process when they assemble a pack. The cells are tested and similar ones are grouped together. Thus cell performance is close. This means the pack with matched cells will stay in balance better than a selection of packs wired in series.

If you have a good high wattage 8s cpable charger 1 8s pack will be mucg easier and quicker to charge. If you have 4 smaller chargers that can only do 4-5s lipo then having the 2s packs may be better.

You will have more complex and lengthy wiring for the 4 2s packs, which will hinder performance somewhat. I would say that if you can package a 8s pack in your rc that would be best. Fail that, 2 4s packs would be the next best suggestion, with a charger and wiring harness that can balance charge those 2 packs together.
   
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suicideneil
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01.01.2011, 11:03 PM

Quote:
---
There must be some where to get 6mm mod1 pinions nearby europe ? do rcm sell this ?
---
can rcm-shop please post high detail images, and specifications of the slipperential ?
6mm pinions arent very common, but they do exist:

http://204.186.93.64/PinionsMod1.htm

You could also drill out a 5mm bore pinion if you have a lathe, or there is always http://www.sdp-si.com/ who can custom make pinion gears.

Detailed diagrams of the slipperential arent available due to scumbags copying the design and selling it from China ( they actually bought one and then reverse engineered it, but all the same ). There is a forum section explaining how it works though if that helps: http://www.rc-monster.com/forum/forumdisplay.php?f=45

As for motor & battery choice, it helps alot to know the exact vehicle and what you are trying to achieve with the setup, rather than just working from the known weight and transmission/ differential ratios.
   
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Question 01.02.2011, 10:17 AM

e-revonut> thanks for clarifying :)

briang> thanks ditto :) i never use rollout, i know those calculator pages too, the way i see it, rollout is to maintain a rel.ship between torque and speed? i did some reading and some things look odd. like on this page:
http://www.rcuniverse.com/forum/m_3255405/tm.htm

where its written "Question 1: What size spur gear should I run? What about the pinion gear?
Well……. When selecting the spur gear and pinion gear size, you need to
understand that there is a direct ratio between the tire circumference (referred
to as roll-out) and the final drive ratio. That ratio, in most cases, should be
as should be as close to 1 to 1 as possible. 1 to 1? What? By a 1 to 1 ratio, I
am referring to one revolution of the tire to one revolution of the motor.
In
doing so, we do our best to maintain the overall efficiency of the motor by
keeping it in the ‘Sweet Spot’. Here’s how..."

the bolded quoting sounds like zero gearing to me ? also, he mentions efficiency in percentages, as for rollout ratio, why is efficiency even in here, no matter the size of wheels and tires..the drivetrain is geared. i would assume that zero gearing would have the least in-efficiency. not that it matters, does it ? yes, a much-geared drivetrain would have some inefficiency, but that doesnt mean one should try to go with the least geared drivetrain does it ?

and a quote on the efficiency:

"We can check our overall efficiency by dividing the
roll-out by the final drive ratio. In this case, the 10.2101 roll-out, and the
10.44:1 final drive ratio means that we have less than a 3% total loss in
efficiency
. In other words, the tire turns 0.977 times, for every 1 revolution
of the motor
. Generally, it is best for your motor to gear your vehicle within a
+ or - 10% margin. ( In the case of this formula, +1 to -1 is an acceptable
margin.) "

..i dont see how that efficiency is logic. would it be 'top speed' instead of efficiency ? it may mean that 3 % of speed become 3% of torque or vice versa, as thats all a rollout is ?

where does the idea behind rollout 1:1 inherit from, i checked my esavvy for rollout and seems it IS pretty close to 1:1 (inch) rollout with the stock 20t pinion, all stock setup. so i figure rollout is good for defining a speed/torque.

but, speed/torque is 'defined' by the motor ? if one slaps a torqier motor on, gears less in drivetrain, the rollout is eventually changed. so using briang's calculator my rollout now is 1.8:1, i dont see how that can be 'inefficient'. on the post from rcu, i should take my final drive gearing (10.2) and deduct rollout (18.5") - now where on earth does that bring me..

i did check the rollout on stock stampede vxl too, rollout is pretty close to 1:1. Now, with 3s and spur/pinion changes, the rollout is then 2.2:1

i dont think there's such a think as inefficient rollout. ?

btw, i find it more useful to look at the 'axle torque' using briang's calculator. less axle torque= more top speed. and then eventually using a temp meter

thanks for replying guys i appreciate it. i will read up on the posts now ;)

Last edited by Aero; 01.02.2011 at 10:20 AM.
   
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suicideneil
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01.03.2011, 03:41 PM

Quote:
..i dont see how that efficiency is logic. would it be 'top speed' instead of efficiency ? it may mean that 3 % of speed become 3% of torque or vice versa, as thats all a rollout is ?
The 1:1 rollout ratio is just a good guideline to try and prevent beginners from entering unrealistic numbers in order to create a speed machine from unsuitable components. More advanced users will know that they can use a taller overall gear ratio if their motor, esc and batteries are suitable, but some young people who are new to the hobby usually make their post something like "how do I make my truck do 100mph?"; if you dont give them guidlines to follow, then they will only end up cooking somethign expensive without ever figuring out why. 1:1 is close to what most stock trucks have, such as your esavage and the brushed emaxx for example.

Quote:
but, speed/torque is 'defined' by the motor ? if one slaps a torqier motor on, gears less in drivetrain, the rollout is eventually changed. so using briang's calculator my rollout now is 1.8:1, i dont see how that can be 'inefficient'.
Bear in mind the thread on rcu is 5 years old- there are simpler equations to follow these days- or just use the gearing calculator, saves the effort.

As I mentioned before, when you use a more powerful motor, esc and batteries, you can ofcourse gear higher and this causes the roll out ratio to stray away from the 1:1 ratio which is optimum for a lower powered stock setup. Its not so much about there being an inefficient rollout ratio, its more to do with being efficient for a certain setup; a sensible 40mph setup will be much closer to 1:1 vs a speed-run setup which is geared for 70mph for example.

I wouldnt get too bogged down worrying about rollout ratios, its more important to get an understanding of which esc, motor ,battery & gearing combos are best for any given scenareo & vehcile; years of reading and research helps with that, like 'learning on the job' at your work place..
   
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Aero
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Thumbs up thanks - 01.03.2011, 05:53 PM

thanks for the explanation suicideneil. hm does yout avatar come from that game 'my lil bastard' ? well i didnt see that rcu thread was that old i do think its a bit misleading. as im more mislead than stupid of coz

I see the point in relating the 'rollout' to switching wheels, and also once i had a telemetry, to calculate speed (then i saw the interest in rollout). when thinking over it, both an esav and a pede has a stock 1:1 rollout, then that lead me to believe those trucks are designed like that. despite using imperial(inch) the 1:1 ratio seems to 'coincidentaly' ? work as a 1:1 guiding. why that is ? So it's just like that, the rc manufacturer puts on some kind of wheels (diameter) that relate to the gearing - or vice versa. well interesting. Because, the esav has brushed motors, the stampede has brushless motor.

im suspecting it has to do/inherit from standard dc motors ? take it further, relating to a standard kv-rating, or torque values..or something..? any idea why rollout 1:1 is what stock trucks have?

thanks for the pinon link, i would really like to not buy pinions there. i bought a few once, only to get the messages they're sold out, and whether i would like this and that instead. seeing how the MM XL is 'for sale' there and not in stock, instock and out of stock has its own meaning there.

the battery question was merely a theoretical question on the views of cell counts. I dont have any fancy idea of 8s on and e-savage dont even have an 8s esc to whip But I do have an idea of an alza racing savage flux chassis with 4 x 2s and a leopard/toppower motor. (8s wont fit inside)

heres a funny pic (ooh, that why iphone charge so slow!)


I had a bad cell on 3s pack once, i can imagine a bad cell in an 8s pack would be terrifying annoying. where the 4 x 2s would leave 3 x 2s, thats the more 'practical' ideas i was thinking of. (like 2 x 2s could be used in 4 rc's, and fewer cells stacked in a pack) and maybe in an 8s pack, the 6 inner cells, those would be sitting like a can of fish heating up etc.. As i mention the lipo serial wiring was another matter itself (resistance and neatness). still, i dont see why some 10awg wiring resistance (multi-strand and all) would matter THAT much. it would also give some means of relocating 'weight'/CofG on a truck. like to adjust for wheelies and no-wheelies.
   
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