A possible alternative Crawler motor for Large scale rig ....

[A Big Kid]

In my ARRMA Kraton crawler I originally set it with a 2250kv 3542 1/10 scale Outrunner into a planetary gearbox. Now this has worked just great and even tho my rigs near 17 pounds due to such Low low gearing the little 1/10 motor hardly breaks a sweat and has more than sufficient torque.
** Issue is top speed set up as such being @ 10-12 mph at max throttle, might be a tad less than that as it certainly is not faster
* Picture below of the 9IMOD 3542 size Outrunner and gearbox combo.

So ... been searching and searching for a LARGE Outrunner utilizing 5mm shaft output in an @ 42mm diameter ( Same as an OEM BLX 2050 kv ) and came across some Large Scale Aircraft Outrunners ( Marketed as Aircraft but also general use ) that met the wanted specification. So for $30 bucks took the gamble and ordered up the 4250 size in a High Torque 560kv format. * Idea here is to still gear low but run as a direct drive as rig was designed to use.

** Reason I'm staying with Outrunners is COGGING or a near lack of being Outrunners utilize 14 pole 12 slot stator/windings and deliver power very smooth and linear over a conventional Inrunner design. A Very Low 540 KV I'm thinking might be very controllable as well ?


I hope my thoughts align with reality in that set up as such The low end torque will be there in mass, while more topp end speed might result ( Want to stay sub 20mph ) can motor pinion up as needed ... i think ?

Any thoughts ? ... or am I nutz

 

[Doom!]

I would love to say it sounds like a great idea, but I am not knowlegeable enough with electronics to know what I'm talking about. I mean for what it's worth, it sounds reasonable to me.

 

[WickedFog]

You need to figure out your final drive ratio. On 2s, your 540kv motor will be turning roughly 4000rpm at max throttle. How many revolutions does your pinion turn for one revolution of your wheels? What diameter are your tires?

 

[A Big Kid]

You need to figure out your final drive ratio. On 2s, your 540kv motor will be turning roughly 4000rpm at max throttle. How many revolutions does your pinion turn for one revolution of your wheels? What diameter are your tires?

If you can crunch those numbers If I can provide the plug in figures ... That would be grand !!

 

[MVRCA]

"Am I nuts..?"

Well, little of that setup makes any sense, so in many ways you've already planted your flag in the wild custom arena. I'm not sure you can make it much more odd unless you add tank tracks.

Sort out a motor mount and run this: https://www.3brothersrc.com/product...ackjacket-860kv-8s-14-pole-sensored-outrunner

Set up for a small 8s battery. That has enough torque to shred the drivetrain of that ARRMA if you're not careful with the throttle control. I run one in my SCX-6 on 6s.

That said, it would be cheaper to go with this: https://holmeshobbies.com/motors/br...40-l-classic/revolver-540-classic-1450kv.html and get a pinion sorted out. It has plenty of power on 4s.

 

[A Big Kid]

"Am I nuts..?"

Well, little of that setup makes any sense, so in many ways you've already planted your flag in the wild custom arena. I'm not sure you can make it much more odd unless you add tank tracks.

Sort out a motor mount and run this: https://www.3brothersrc.com/product...ackjacket-860kv-8s-14-pole-sensored-outrunner

Set up for a small 8s battery. That has enough torque to shred the drivetrain of that ARRMA if you're not careful with the throttle control. I run one in my SCX-6 on 4s.

That said, it would be cheaper to go with this: https://holmeshobbies.com/motors/br...40-l-classic/revolver-540-classic-1450kv.html and get a pinion sorted out. It has plenty of power on 4s.

View attachment 210551

Well .. Not sure you have read where I'm at ... as the Outrunner I'm already using threw the planetary is very similar to Revolver, tho higher KV.
The large Black jacket is also very similar ( It not made by the same chinese mfg ) to what I have coming and speaking about in this thread ( Tho a tad lower KV and not sensored )

Come end of the day the project by design while assembled with great thought and mechanical QC, is being done on the cheap !!
Yes I LIKE, No LOVE "Wild Custom" which was kinda the point

Here is the Spec break down on the Big outrunner coming this way ... FYI

4250 560kv [Power32]​

Motor diameter: 42mm​

Motor height: 48mm​

Shaft diameter: 5mm​

Output shaft length: 20mm​

KV value: 560KV​

Maximum power: 1760W​

Voltage: 11.1-36V​

Speed: 5600-9800rpm​

Torque: 0.8-1.2 N/m​

Stall torque: 7-8N/m​

Winding number: 9​

Number of motor poles: 14P​

Stator slot number: 12N​

Resistance: 0.068Ω​

No-load current: 1.5-1.6 A (maximum current 80A)​

Banana connector: 3.5/4.0mm​

Lithium battery section number: 3-8S​

Mounting hole size: M3*4​

​

 

[MVRCA]

Sounds like you have a plan. Good luck.

 

[A Big Kid]

Sounds like you have a plan. Good luck.

Thank you ... Motor swaps are the easiest thing to do and is part of the hobby especially when out there in "Wild Custom" territory

 

[A Big Kid]

You need to figure out your final drive ratio. On 2s, your 540kv motor will be turning roughly 4000rpm at max throttle. How many revolutions does your pinion turn for one revolution of your wheels? What diameter are your tires?

Wicked Fog ... If you would PLEASE ...

14 tooth pinion on a 46 spur equals 3.286 motor revolutions per 1 revolution of center diff
3.4 rotations on center diff equals 1 wheel revolution.
Tires are 7.3" tall

Running on 4S
Motor KV 560
* Theoretically at 14.8 volts equals 8,822 rpm at WOT

** Vehicle speed at WOT would be ?

Can you work with that ?

 

[WickedFog]

Calculate your pinion/spur gear ratio:
Pinion: 14t
Spur: 46t

46 ÷ 14 = 3.286 motor revolutions to one spur revolution, or 3.286:1. This is commonly referred to as your gear ratio.

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Now we need the final drive ratio, which is how many times the motor rotates for one revolution of the tire.

• Pinion to spur is 3.286:1
• Transmission ratio is 3.4:1
• Multiply 3.286 x 3.4 = 11.1724:1

So your motor rotates 11.1724 times per one revolution of your tire, which is the final drive ratio.

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Figure your rollout, which is how far your truck will travel during one revolution of the tire.

Your tire diameter is 7.3"
Multiply that by pi, which is 3.14
7.3 x 3.14 = 22.922" travelled per one tire revolution.

So your tire rollout is 22.922"

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Calculate motor revolutions per hour:

Motor kv is 560
Battery voltage is 14.8v nominal
560 x 14.8 = 8822 rpm at WOT

Convert to hours
8822 x 60 = 529,320 rph at WOT

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Now we need to figure out how many tire rotations that is in an hour. Divide the number of motor rotations per hour by your final drive ratio

529,320 ÷ 11.1724 = 47,377 tire rotations per hour.

So your tire will rotate 47,377 times in an hour.

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We need to know how far that is in inches. So multiply that by the circumference of the tire, which we found to be 22.922"

47,377 x 22.922 = 1,085,975.594 inches travelled per hour.

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Convert that to miles. There are 63,360 inches in a mile. So divide your value by 63,360

1085975.594 ÷ 63360 = 17.1397663194 mph

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This is the average mph per pack because we used the nominal value of 14.8v for your voltage. It will be faster at full charge of 16.8v

* You can try refiguring it for max voltage of 16.8v to find out the actual top speed

Note: I'm old, getting senile, and I lost track of where I was at least 3 times figuring that out. I could be way off. So if anyone wants to doublecheck me please do.

* The solution is 18.2784524201 mph

 

[Doom!]

Calculate your pinion/spur gear ratio:
Pinion: 14t
Spur: 46t

47 ÷ 14 = 3.286 motor revolutions to one spur revolution, or 3.286:1.

Now we need the final drive ratio, which is how many times the motor rotates for one revolution of the tire.

• Pinion to spur is 3.286:1
• Transmission ratio is 3.4:1
• Multiply 3.286 x 3.4 = 11.1724:1

So your motor rotates 11.1724 times per one revolution of your tire.

Figure your rollout, which is how far your truck will travel during one revolution of the tire.
Your tire diameter is 7.3"
Multiply that by pi, which is 3.14
7.3 x 3.14 = 22.922" travelled per one tire revolution.

So your tire rollout is 22.922"

Motor kv is 560
Battery voltage is 14.8v nominal
560 x 14.8 = 8822 rpm at WOT
Convert to hours
8822 x 60 = 529,320 rph at WOT

Now we need to figure out how many tire rotations that is in an hour. Divide the number of motor rotations by your final drive ratio

529,320 ÷ 11.1724 = 47,377 tire rotations per hour.

So your tire will rotate 47,377 times in an hour. Now multiply that by the circumference of the tire, which we found to be 22.922"
47,377 x 22.922 = 1,085,975.594 inches per hour.

Convert that to miles. There are 63,360 inches in a mile. So divide your value by 63,360

1085975.594 ÷ 63360 = 17.1397663194 mph

This is the average mph per pack because we used the nominal value for your voltage.

You can try refiguring it for max voltage of 16.8v to find out the actual top speed

Note: I'm old, getting senile, and I lost track of where I was at least 3 times figuring that out. I could be way off. So if anyone wants to doublecheck me please do.

Dude! I think you might have just caused me some permanent brain damage. I don't math good.

 

[WickedFog]

Dude! I think you might have just caused me some permanent brain damage. I don't math good.

My brain is still smoking

 

[A Big Kid]

THANK YOU ... not doubting, but just sub 20 mph is ideal. Q becomes if or not the start up / motion threshold has sufficient torque and lack of cogging to crawl with some degree of control.
* We'll know by next weekend.

Again, THANK YOU very much

 

[WickedFog]

You're welcome. Let us know how it works out.

 

[A Big Kid]

Motor got here today.
Need to change out the wiring connectors from 3.5's to 4mm before the testing proceeds.
Win ... loose, or Draw ... it is a hobby

 

[WickedFog]

I hope it works out for you. Let me know how close I was to guestimating the top speed

 

[A Big Kid]

Wickedfog ... your number crunching was correct, or as close as I'm able to measure

Which leads to "How Did" the 560 kv work ?
For speed wanted excellent, mid range torque having smooth transition up/down very good .... Low end grunt .. poop !!!
When up against an obstacle basically locked in stopped ( The 17-1 gearbox & 2250kv outrunner would spin up and create motion ) where this 560 kv direct drive COGGS and shutters sending ESC into motor control black out

So without a miens in allowing any brushless motor to spin up a bit, running crawler like on the mechanical architecture / transmission or a lack of, a ARRMA 6S vehicle is not happening set up as such. * The Previous Outrunner into a 17-1 reduction actually works great !! Tho lacks speed much better than +/- 10 mph.

So we enter PLAN C ..... Beefing up the gear box to 5mm input and 5mm output in a 42mm size at a 3.7-1 ratio, we can get back close to the original set up with a tad more speed, yet in specification have some tougher parts in motor and reduction gear box size. * Utilizing the Big 565 KV outrunner

Now my math might be a tad fuzzy, but here is what numbers I crunched ...

BASED on 15 volts ( Fully charged 4S ) battery.

*2250 kv = 33,750 rpm
17 to 1 reduction = 1,985 rpm at gearbox output.

*565kv = 8400 rpm
3.7 to 1 reduction = 2,270 rpm at gearbox output

Or .. use the OEM 2050 BLX motor threw the 3.7-1 gearbox ?
*2050 kv = 30,750 rpm
3.7-1 reduction = 8,310 at output * being very close to the 565 kv used as direct drive ... Huh

Another planetary gearbox ( The 3.7-1 ) is @ $34.00 .... Cheap compared to busted parts bashing !!

We have a VERY functional rig with the 17-1 2250 combo, just worried it is too light duty to drag around near 17 pounds of truck for very long.

 

[CertifiedMike]

At some point in the math, right before my head was about to split open, I had an epiphany...
THROW A HEMI IN IT!!!

The mathing has been rather interesting honestly.
Thanks for all the gearing/roll out/speed explanations @WickedFog!!!