Help with Turnigy RC motor

[iangreenhalgh]

Hi folks

I just happen to have a Turnigy SK3 motor that has a max current of 110A, a max voltage of 30V, for a 3000w rating. Sounds good so far, but it does 1500rpm per volt.

The drive system on the bike I'm building uses a 4.75:1 reduction gearbox with an 11t drive sprocket connected to a left hand side mounted 99t sprocket on the rear axle, which gives me a 42.75:1 overall reduction (4.75 x 9).

The back wheel of the bike is a Michelin M45 80/80/16 motorbike tyre on a 20 inch BMX wheel, the outer diameter of this combo is about 22 inches. Therefore I want the max rpm of the drive at the axle to be 450-500rpm, which will give me ample speed.

If I multiply 500 by 42.75, that tells me the max rpm of the motor = 21375rpm.

If this motor does 1500rpm per volt, dividing 21375 by 1500 will give me the required voltage to achieve that motor speed = 14.25 volts.

So, if my maths is right, the maximum I should give this motor is 14.25votls. Hmm, that fits pretty well with four li-on cells in parallel.

So now I'm thinking, I can use this motor with a 12v controller and make a battery from 18650 cells that is 4S (the motor is rated for 8S Li-po). I've got a couple of hundred 18650s from recycled laptop batteries, so I could make a 4S 32P pack using 128 cells and giving me roughly 64Ah at 14 volts assuming 2000mAh cells, if my cells are a bit more on the worn out side and only providing 1500mAh apiece I should still get 50Ah.

How does this sound? I'm bound to have overlooked something. Sensible critiques and comments please.

 

[Thud]

Hello,
Your math is correct.
If I may ask, which motor exactly are you looking to employ? something in the 35mm class it apeers.

My phylosophy is to modify the reductin requiered to keep the motor spinning in an efficent rpm zone.
Your described set up sounds feasable.

If your using a 1500kv motor from hobby king, it is being advertised at a maximum perfotmace figure.
Are you certain the motor is rated to 8 cells? (that gets you more than 49k rpms)

You will need to spin the motor at or near its rpm limit to realise its power potential.

I cant find a motor on Hk's with a kv greater than 1k that lists more than 3cells Lipo capability (12.6v)
Most of these are rated for a recomended peak of 35 amps. This is less than 500 watts of energy potential (again at peak performance)

I suggest you be very aware of the power you feed the smaller motors. They have limmited mass to deal with any excces heat you may generate.

The only other comment/question I have: A 60ah battery pack is huge. Is this for a cargo hauling set up?

Good luck.

Edit: Ijust read your controller question thread.....this is an inrunner? If that is the case....re-read the comments about spinning your motor to the correct rpm to achive anyrhing resembling the quoted power ratings of the motor.
With this information you need to re design you reduction to provide 99-1 redux efficently.

 

[iangreenhalgh]

Hi Thud

Much appreciate the help, cheers.

Here is the motor:

http://www.hobbyking.com/hobbyking/store/__47362__Turnigy_SK3_90mm_8S_3000w_Fandrive_Brushless_EDF_Motor_3968_1500KV_UK_Warehouse_.html

On the motor is written Turnigy SK3 Fandrive EDF 8S 90mm 1500kV

I wrote down the specs:

Kv - 1500
Weight - 363g
Max Current - 100A
Max Voltage - 30V
Max Power - 3000w
Shaft - 8mm

Some more specific details on my drive system:

The gearbox is from a Makita GA9050 9" 2kW angle grinder; it appears to have a reduction around 4.7 or 4.8 to 1. I haven't counted the teeth on the bevel gear, just marked a dot on the output shaft and turned the input until the output rotates 360 degrees and count the number of input turns - almost 5.

I mounted an 11 tooth sprocket on the output shaft, this will drive a large sprocket on the left side of the rear axle, mounted on an ACS Southpaw freewheel. The largest sprocket I could find was 99 tooth, but I also have a 64 tooth one and any other size between is a very cheap purchase. I still have to weld the large sprocket to the freewheel, so that ratio isn't set in stone yet. However, if I use the 64 tooth, it will give a 5.8:1 reduction (64/11) and combined with the gearbox, that will give approx. a 28:1 reduction. If I go for a larger 99 tooth rear sprocket, I can get approx 42:1.

I bought the appropriate water jacket to cool the Turnigy motor, I planned to use a 12v fuel pump with a radiator and reservoir from PC cooling equipment to cool the motor.

On the battery, I just happen to have a couple of hundred 18650s and I plan to mount the pack inside the frame using a large triangular bag that fills the entire frame and should hold 128 cells plus BMS no problem. So I plan to use around 128 cells to make the battery, and if the voltage is low, around 14-15v, that means a lot of cells in parallel for high amperage. Cargo hauled will not be much, mostly camera equipment stuffed into the rear pannier bags. However, I'm a rather large person, weighing about 320lbs (hoping to reduce that somewhat through biking) so I felt some significant oomph would be needed to cope with my considerable frame and weight.

 

[goa604]

Personally think at the end of it all it would be cheaper to rewind or buy a lower kv motor.
This way youre going to have a very complicated transmission. My guess is jackshafts, multiple stage planetary gear sets or cycloidal gears.
Not saying it is impossible but it doesnt make much sense.

 

[iangreenhalgh]

Yeah, a different motor is the way to go. I am looking at a 24v brushless with hall sensors that is good for about 600w.

 

[renaissanceMan]

Yeah, a different motor is the way to go. I am looking at a 24v brushless with hall sensors that is good for about 600w.

To clarify, what would your gear reduction setup be if using the 24v motor? Motor - gearbox- rear sprocket? Or.. motor - jackshaft - rear sprocket? Or.. Motor - rear sprocket?

Also, may I ask why you are choosing to drive the back wheel directly, rather than "driving" the cranks to make use of the bike's gearing? Curious if its intended application calls for the use of "1 gear", mainly (And if so, what kind of speed/range tests results will come )

 

[iangreenhalgh]

Hello

I have a gearbox with approx 4.7-4.8:1 reduction, I have fitted an 11 tooth sprocket to the output shaft. This will drive the sprocket mounted on the left using the southpaw freewheel. The overall reduction depends on what size sprocket I put on the rear. The freewheel has 16 teeth, which would give a 6.9:1 overall reduction but I was planning to fit a larger rear sprocket to achieve a much higher reduction to cope with a high rpm motor. A 64 tooth rear sprocket would give me a 27:1 overall reduction.

I chose to avoid touching the bike's existing drive train so the electric bit is optional in use - I intend to have three operating modes - pedal only, pedal assist and throttle.

I will be using the bike to get around the local area, which is very rural and pretty hilly, so I favour torque over speed - I want it to drag me up a big hill at 10mph rather than shoot me along a flat straight at 50 as we have plenty of big hills and flat straights are rather rare here. The maximum distance I can see me venturing from home is less than 10 miles.

This is the motor I am contemplating using instead of the Turnigy:

http://www.ebay.co.uk/itm/24v-Brushless ... xyJX9SH1iC

It's a 24v brushless dc motor with hall sensors. Made by a division of Northrop-Grumman for demanding medical and industrial applications so should be a very high quality item.

Here's the data sheet:

http://spurgeon.spurgeontech.com/scoote ... -specs.pdf

The motor is rated at around 500w and 7100rpm, 22A current. Constant stall torque is 0.3390 to 0.6991Nm and peak torque is 1.2499 to 2.5633nM.

I don't know if that is a lot of torque or not!

7100 rpm would need a 14:1 reduction to achieve 500rpm at the rear wheel, which would be 33mph with a 22" wheel.

I think 1'd like to gear it a bit lower than that as I'm no speed demon. Using an 11t sprocket on the gearbox to a 64t on the rear axle would give me 27:1 reduction which would give a more sensible 17mph at 7100rpm.

How does this motor sound as a replacement?

 

[ferret]

How are you planning to mount the southpaw freewheel to the hub?

Avner.

 

[iangreenhalgh]

The hub has threads on both sides.

 

[Thud]

is the left side a left hand thread?

 

[iangreenhalgh]

Yes, hence you have to use a southpaw freewheel - left-handed threads.

It's fairly common for bmx hubs to be double sided as some riders prefer to grind on the right hand side so use a left hand drive.

You can buy double sided hubs from China but they are not very beefy, more for a racer type bike than an mtb. They are often called 'flip-flop' hubs as in the past, road racer types would mount a cog on both sides, of different tooth numbers, then swap the wheel around one way or the other to select between them.

 

[Thud]

Any link's for the reverse lh threaded hubs?

My only source is Staton & their axil is terrible & all I find in searches are the flip-flop hubs with standard 1-3/8-24 on the flip & std 30mm -1 on the flop

thx.

 

[renaissanceMan]

Hello

I have a gearbox with ...

This is the motor I am contemplating using instead of the Turnigy:

http://www.ebay.co.uk/itm/24v-Brushless ... xyJX9SH1iC

It's a 24v brushless dc motor with hall sensors. Made by a division of Northrop-Grumman for demanding medical and industrial applications so should be a very high quality item.

Here's the data sheet:

http://spurgeon.spurgeontech.com/scoote ... -specs.pdf

...

How does this motor sound as a replacement?

Both links are bad, or I'm a dufis . Please edit or repost

 

[Miles]

Any link's for the reverse lh threaded hubs?

My only source is Staton & their axil is terrible & all I find in searches are the flip-flop hubs with standard 1-3/8-24 on the flip & std 30mm -1 on the flop

thx.

Hi Todd,

I've got Profile BMX one, if that's of any use? 110mm O.L.D. though....

Gru-Bee used to do a 135mm one. No idea what's happened to them....

Ref: https://endless-sphere.com/forums/viewtopic.php?f=28&t=9586&start=15

 

[iangreenhalgh]

Any link's for the reverse lh threaded hubs?

My only source is Staton & their axil is terrible & all I find in searches are the flip-flop hubs with standard 1-3/8-24 on the flip & std 30mm -1 on the flop

thx.

Here's a seller in FL with a double sided hub with the larger imperial size threads either side to fit a standard size freewheel:

http://www.ebay.co.uk/itm/Double-threaded-hub-36H-3-8-Axle-for-single-speed-sprocket-Disc-brake-/281874989671?hash=item41a10f0267:g:qzUAAOxy4dNS5ERX

 

[iangreenhalgh]

Hello

I have a gearbox with ...

This is the motor I am contemplating using instead of the Turnigy:

http://www.ebay.co.uk/itm/24v-Brushless ... xyJX9SH1iC

It's a 24v brushless dc motor with hall sensors. Made by a division of Northrop-Grumman for demanding medical and industrial applications so should be a very high quality item.

Here's the data sheet:

http://spurgeon.spurgeontech.com/scoote ... -specs.pdf

...

How does this motor sound as a replacement?

Both links are bad, or I'm a dufis . Please edit or repost

The links were indeed broken, thanks for the heads-up.

Here are the correct links:

http://www.ebay.co.uk/itm/321962354610?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

http://spurgeon.spurgeontech.com/scootertech/litton-motor-specs.pdf

I also found mention of this motor being used on an electric scooter:

http://www.evdeals.com/DynoData.htm/DynoSII.htm

The new brush-less PWM motor, a Litton model BN34-25AL-04LH with large 15/32" shaft, is quiet and extremely controllable at slow speed. In fact, combined with the well designed electronic controller board and finger operated throttle, I was able to maneuver around the shop at speeds well under 2 mph with total speed control. (something I’ve never been able to do with other scooters) A temperature strip, indicating 86 to 140deg F is attached to the motor body and easily readable. Under full speed testing, the motor case temperature never reached maximum, and no sign of overheating was observed.