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Toolmaker72

Early Subaru Brat locked diff ratio?

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So I have an early Subaru Brat locked diff gearbox fitted with a 380 motor and I assume it’s a 10 tooth pinion the same as a monster beetle pinion.  Now was wondering how many turns of the motor per revolution of the wheel, compared to the monster beetle gearbox? 
If anyone knows please?

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Well, I’ve ordered a little 2845 brushless motor to replace the brushed 380 motor.  Having a measure and a monster beetle brass pinion will fit the new brushless motor and is dimensionally the same tooth wise as the pressed on 380 motor pinion.  A couple of 3s lipo batteries are also on the way with a suitable esc.  I’m intrigued if this low geared little motor will knock the socks off my regular now vintage 27 turn stock motors.   
Also lockdown part 3 has just been confirmed so wizzing up and down the road soon should be fun 😊   

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The test drive in the kitchen shows promise. Not slow at all.  Not sure of top speed performance yet as I’m using a 10 pinion.  The little brushless motor is impressive with the 3s lipo battery though. I’ve briefly tried the 3s lipo battery with a brushed motor and yes it’s spins faster as it’s putting more volts into it I wouldn’t say the brushes would last long as clearly lots of commutator sparks can be seen.  

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I found this post, and it helped:

but in summary:

Frog STD:

50/18 x 47/18 = 7.25 (7.3 in manual)

Frog Speed:

49/19 x 47/18 = 6.73 (6.7 in manual)

Frog Torque:

52/16 x 47/18 = 8.48 (8.5 in manual)

Blackfoot:

52/10 x 48/17 = 14.68

OG Brat:

50/10 x 46/19* = 12.1 (* assumed as I could not find the teeth count of the OG Brat Idler gear (the small one on the Spur gear that contacts the Diff gear).

This is also with the OG 380 motor, so take that into consideration.

If you use a BF motor mount and 10t pinion, the numbers will be the same, but with the added power of the 540.

If you choose to switch to a Frog pinion and 540 motor, you can plug-and-play the 18t pinion, in which case the math is here:

50/18 x 46/19* = 6.72 (* as above)

Based on these numbers, it looks like the OG Brat gearing is comparable to the Frog Speed gearing.

Assuming all my math is correct...

Terry

 

 

 

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Yeesh, I need to take a look at my Blackfoot gearing. I'm running a 16T pinion somehow??

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48 minutes ago, Frog Jumper said:

I found this post, and it helped:

but in summary:

Frog STD:

50/18 x 47/18 = 7.25 (7.3 in manual)

Frog Speed:

49/19 x 47/18 = 6.73 (6.7 in manual)

Frog Torque:

52/16 x 47/18 = 8.48 (8.5 in manual)

Blackfoot:

52/10 x 48/17 = 14.68

OG Brat:

50/10 x 46/19* = 12.1 (* assumed as I could not find the teeth count of the OG Brat Idler gear (the small one on the Spur gear that contacts the Diff gear).

This is also with the OG 380 motor, so take that into consideration.

If you use a BF motor mount and 10t pinion, the numbers will be the same, but with the added power of the 540.

If you choose to switch to a Frog pinion and 540 motor, you can plug-and-play the 18t pinion, in which case the math is here:

50/18 x 46/19* = 6.72 (* as above)

Based on these numbers, it looks like the OG Brat gearing is comparable to the Frog Speed gearing.

Assuming all my math is correct...

Terry

 

 

 

Thank you.   I’m using a brushless 2845 which is roughly 380 size, mounted to the gearbox via a grasshopper 380 mount fitted with a Blackfoot 10 tooth pinion.   With the 3s lipo the motor can spin at 50k rpm.  So with that gearing it’s roughly equivalent to a very hot brushed 540 motor of 27k rpm fitted to a standard ratio gearbox.  
I made a conversion plate for that 2845 motor to run in a 540 fitment so will give it a run like that soon to see if it has enough torque with a higher gear ratio, gut feeling says it will be fine.    
 

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