rc motor no reduction drive?

[ev_nred]

hello everyone!
just been thinking about something is it possible to run an rc motor with no gear reduction? i know that it will efect the torque, but I just cant stop thinking about how epic these motors are like 6KW and 250kv, also are there any problems with under powering a motor, lfor example runing a 7kw rc motor on 42amps and 44.4v (2kw)
thanks so much!

 

[Miles]

No reduction? You're planning to use it as a hub motor?

Most friction/roller designs are direct drive.

 

[ev_nred]

No reduction? You're planning to use it as a hub motor?

Kepler's roller drive design uses the can of the motor to drive the tyre.

my bad what i meant was to use the motor with out a 2-stage reduction drive juest a dirct chain drive.

 

[Miles]

No problem......

A drive with one chain or belt between the motor and the wheel is a single stage drive. I really think we should stop calling it direct drive, it's just too confusing... It's not your fault, though.

You can run these motors at slower speeds, the power available falls off more or less in direct proportion, as you already understand. The efficiency falls a bit, too.

 

[Jeremy Harris]

You need a pretty massive rear sprocket, but it can be done. If you search the forum you'll find at least one member has made a really big rear sprocket to do just this - it's not a part you can buy off the shelf, unfortunately, at least AFAIK.

Jeremy

 

[Miles]

There are a few single-stage builds on the forum which use the Golden Eagle drive pulley. This attaches directly to the wheel spokes.
http://www.bikeengines.com/orderpage2.htm [scroll down]

See: http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=9172

 

[spinningmagnets]

Here's Thuds RC race-bike...clear plastic sprocket on the large-diameter end. Vuelta makes a 60-tooth chainring for $40, and Recumpence makes a $49 adapter to attach a chainring to the disc brake boss on the left side of a rear wheel.
http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=7192&start=15#p178174
http://endless-sphere.com/forums/viewtopic.php?f=28&t=11690#p178009

If you use #219 chain (smaller links) it allows you to use a smaller motor-cog, and you might find large diameter #219 sprockets at a Kart website.
http://www.cometkartsales.com/store/sprocket/extron.htm
http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=7192


Turnigy makes an 80-85 motor with a low 170-kV, and also an 80-100 with a low 130-kV
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=5141
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=5142

 

[ev_nred]

thanks everyone the golden eagle looks like a good option,i was thinke about runing the 250kv 6kw hobbykign motor will it work with it at 2kw? how will the will it be possible to get it to %90 efficent

 

[Miles]

Can you post a link to the motor?

 

[ev_nred]

heres the link: http://hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=5140&Product_Name=HXT_80-85-A_250Kv_Brushless_Outrunner_(eq:_70-40)
also would standered motorcycle sporkect work? will the battery be okay at 2kw
thanks so much!

 

[Hillhater]

If you are going to go with a single stage reduction, you will need to have a motor with a low KV, or your gearing will be way off.
As previously suggested by Spinningmagnets maybe this one @ 130kv ..
http://www.hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=5142&Product_Name=Turnigy_80-100-B_130Kv_Brushless_Outrunner_%28eq:_70-55%29
also ,those go kart chain drive sprockets are available for 10:1 reductions ( 9T - 92T )... but you will need to engineer the fittings.
Motorcycle sprockets wont get you anywhere near the gear ratio, and the chain is way too big / heavy (#480 & #520)

also , make sure you are aware of the RC motor/controller limitations and "issues" !

 

[MitchJi]

Hi,

Here's one example:
http://endless-sphere.com/forums/viewtopic.php?f=28&t=12267

I figured it was time for a new thread, so I could stop cluttering up others with bits and pieces on this direct-drive stuff. Anyway, what I'm doing is using an AstroFlight 7-turn 3220 (kV: 97) to directly drive a 3-speed hub on a 20-inch West Marine Port Runner folding bike...

This steel cog is sandwiched between a 22T 4-hole 64mm BCD "granny gear" aluminum mountain bike sprocket, and a 94T aluminum #35 heavy duty go kart sprocket I got from gokartgalaxy.com...

The #35 sprockets and chain are much wider than even the 1/8" BMX chain/sprockets. I like this a lot. Very robust, and will certainly handle the power/torque the 3220 puts out. The finer pitch (3/8" vs 1/2"...) allows for higher ratios, which is really what makes this direct-drive setup possible.

I'm currently using an 11T motor sprocket (also from McMaster...), which gives a reduction to the hub of 8.55:1. These 3-speed hubs have 1:1 ratios in 2nd gear, and about 1:0.75 in 1st. That bumps up the reduction is 1st to about 11.4:1. Third gear is like "overdrive", and has a reduction of 1:1.33. This ends up giving unloaded top speeds of about 22 mph in 1st, 29 mph in 2nd and 39 mph in 3rd.

Points to note:

• His motor has a kv of 97
  Three speed hub (more reduction in the lowest gear).
  20" rims (more reduction).
  Gave up on RC esc's (blown too many, lack of sufficient reduction is a primary cause)
  Pretty close to the limit for single stage reduction on that bike.
  The 11T motor sprocket makes for a pretty noisy drive.

The belt on the wheel sounds like a good idea.

A motor with a kv of 250 is not a good idea.

 

[ev_nred]

thanks for the reply! yeah after looking at the motors the 250kv is over kill, the 130kv is beter. I know about the problems with esc but Ill be under powering it so I thinke it will be okay (runing a 100amp esc at 50 amps) (tell me if im wronge)

 

[jmygann]

what about a 75 KV motor .....

single reduction .....

for more reduction ... SRAM DD internal hub ..

 

[ev_nred]

thanks for the info!
isnt that the 12kw $250 motor? anyways its over kill! (but would be fun as hell ) btw, has anybody mange to get a #35 chain 12mm bore motor sprokect if so were? thanks!

 

[jmygann]

Best low Kv motor ? 7-12 Kw ?

$180 ?
http://endless-sphere.com/forums/viewtopic.php?f=31&t=20292

 

[MitchJi]

Hi,

isnt that the 12kw $250 motor?

I'm not sure if its this 75kv motor but this one would be a good choice:
http://endless-sphere.com/forums/viewtopic.php?f=31&t=20292#p296294

While we are pimping Colossus , here is our second motor out of 5 planned for Colossus ev motors website

The power 7kw - peak
75kv - lower kv for more simple bicycle setup . Plan is to run them without gearbox , just sprocket reduction

12 poles , 14 mags The diameter of the stator is 68mm, and the length is about 55.6mm

This motor is a little longer then usual turnigy or hxt motors and has NSK bearings

Motor Sample Voltage Current at no load Speed
Green 30V 2.0A 2270rpm
Red 30V 2.OA 2300rpm

They are known to change prices especially when dollar is running wild and Euro( Croatian kuna is based on Euro) .... but somewhere from 150 -180 dollars + shipping from China (express cost me 80 dollars for two motors ) .

 

[ev_nred]

il stick with the 130kv or 170kv motors form hk but those anybody know where I can get a 12mm diamter dore motor sprokect for #35 chain? thanks for the help!

 

[MitchJi]

Hi,

anybody know where I can get a 12mm diamter dore motor sprokect for #35 chain? thanks for the help!

You might need to have some machining done. BTW #219 chain has a slightly smaller pitch than #35 chain and since its used for Go Kart Racing there is a better selection of high quality #219 chain. I think Gary calculated (the limiting factor is space for the big sprocket) he could increase his tooth count on his small sprocket by one tooth (to reduce the noise a little) and use a large #219 sprocket the same size but it would have enough extra teeth to get the same overall reduction.

I know about the problems with esc but Ill be under powering it so I thinke it will be okay (runing a 100amp esc at 50 amps) (tell me if im wronge)

It probably depends on how you use it. The best way to kill one is with a high load at low rpm, which is greatly exacerbated if you have insufficient reduction. But if you pedal to get moving it might be ok. OTOH if you do full throttle starts from a standstill it probably won't last very long.

 

[Hillhater]

thanks for the reply! yeah after looking at the motors the 250kv is over kill, the 130kv is beter. I know about the problems with esc but Ill be under powering it so I thinke it will be okay (runing a 100amp esc at 50 amps) (tell me if im wronge)

Sadly, these RC systems dont always work the way you would expect them to !
you may be lucky and assemble a working system, but dont be surprised if you have issues.
I would seriously consider using a sensored motor and a proven Ebike controller to avoid the potential RC hiccups !

 

[spinningmagnets]

To start with, what diameter of wheel do you want to use, 20"...24"...26"? Also, what do you need the top speed to be? If you at least 'consider' that you may need a jackshaft to add a reduction on top of the final-drive, that small additional cost will help with many of the options that can ease design problems. I advise you to study Bubba's build 5, and Muds build also.

http://endless-sphere.com/forums/viewtopic.php?f=28&t=20245
http://endless-sphere.com/forums/viewtopic.php?f=28&t=14734&start=0

 

[ev_nred]

thanks for the reply, the project I want to do with this motor is an electirc motorcycle, now I know what most of you are thinking (this guy is out or his a...mind ) well think about it the project at theworkshop.ca have less power and im aiming for a top speed of 50kmh but would be okay at 30kmh( ) and I wigth under 110lbs migth be less, is it possible? im thinking of useing a 125cc-250cc dirtbike frame

p.s. if so migth start this project in decmber

 

[jmygann]

To start with, what diameter of wheel do you want to use, 20"...24"...26"? Also, what do you need the top speed to be?

I for one would like a 24" wheel .... 48 volt ... 30mph max .....cruise at 20-25mph

Is that doable with the COLOSSUSWRC-7KW -75KV motor ?

10:1 reduction ??

 

[jmygann]

"The approach generally taken is to pick a motor that has a Kv that will allow a bit more than the maximum desired speed, with a realistic reduction ratio. For example, a motor with a Kv of 50, a maximum desired speed of 50mph, a driven wheel tyre outside diameter of 24" (2ft) and a battery voltage of 48V will need a reduction ratio of:

Motor maximum off load rpm = 48 volts x 50 = 2400 rpm
Wheel rpm at 50mph = (5280 ft /60 mins) / (50 mph x 3.142 x 2 ft) = 700 rpm
Reduction ratio required = 2400 / 700 = 3.428 (which is achievable with a near-standard chain drive)"

http://endless-sphere.com/forums/viewtopic.php?f=10&t=18609

so for a Kv of 75 .... and 30 mph ...

Motor maximum off load rpm = 48 volts x 75 = 3600 rpm

Wheel rpm at 30mph = (5280 ft /60 mins) / (30 mph x 3.142 x 2 ft) = 422.5 RPM

Reduction ratio required = 3600/422.5 = 8.5

Is that correct ?

 

[Hillhater]

Mathematically both calcs are correct but you are both assuming that you can achieve no-load rpms at your target speed.
That aint gonna happen ! ... motors wont achieve max NL rpm under load unless they are hugely overrated ( like X 10 !)
you need to estimate or experiment to establish you motors loaded performance.