GRU and T-Case Question

[FireWire79]

So I have another n00b question. Glad they have the n00b section for me, but I seem to get my questions answered quickly.

I plan an using a 10t Cobalt Puller motor in my SCX10 scaler. If I use a GRU like a GD-600 2.5:1 and a 1:1 t-case, would this totally decrease the top speed that I am trying to get out of the rig in the first place?

[pantablo]

the standard transmission ratio, I just found out, is about 1:6.2 (just figuring on the 87 spur and 14t pinion). so anything less than that at a gru should be quicker than standard.

[FireWire79]

Ok. Maybe you can help explain this to me. I think I get it but, never hurts to check.
I believe that the normal operation range of motor is somewhere around 25k RPM.

1:6.2 = 1 rotation of the motor equals 6.2 rotations of the spur gear
so 1000 RPM = 6200 RPM
thus 25000 RPM = 155000 RPM at the spur??


by using a GRU and T-case

2.5:1 = 2.5 rotations equals 1 turn of the output shaft
so 1000 RPM = 250 RPM
thus 25000 RPM = 1000 RPM at the output shaft??

Doesn't this imply that the rig will be slower due to the 2.5:1 ratio? Please correct me if I am wrong, and I hope I am. Seems like this would lead to a serious decrease in wheel speed? I'm lost, so get me on the right path.

Just read >>this<< and it is good, just a little beyond my comprehension.

[MadForce]

Originally Posted by FireWire79

1:6.2 = 1 rotation of the motor equals 6.2 rotations of the spur gear
so 1000 RPM = 6200 RPM
thus 25000 RPM = 155000 RPM at the spur??

This part I think you got wrong. The stock 14 pinion/87 spur gearing of the AX/SCX truly comes to ~6.2:1 before the transmission itself. This translates into 6.2 revolutions of the motor=>pinion for one full revolution of the spur gear.

Now if you take into account the 2.6:1 gear reduction the AX/SCX transmission provides through the internal gears then you have a total of 6.2x2.6=16.12 total reduction from the motor to the output shaft.

This means that the motor needs 16.12 revolutions to complete one revolution of the output shaft. If on top of that you add a GD600 with a 2:1 gear reduction then the motor will need 16.12x2=32.24 revolutions for one complete revolution of the output shaft.

[FireWire79]

So if the above is correct, I would assume that by lowering the gear ratio from 6.2:1 to 2.5:1 I should pick up more wheel speed.

As we will be going from 2.5x2.6= 6.5 final ratio at the wheels. When copmared to the 16.12 of the stock drive line, it should equate to more wheel speed and torque with less effort on the part of the motor. Does this seem a little more correct?

The GD600 is going to replace the stock transmission as I need the space and want to keep everything under the hood and looking smooth.

[MadForce]

The above numbers would be true if the output shaft from the GD would couple straight tot he spur shaft of the tranny with no pinion/spur combo. I fail to see how you are going to accomplish this. If you do it using only a gear down and a transfer case as you said in your first post then it would be doable. In this case though your total reduction would only be 2.5:1 not counting the diffs. In short, if I get it right, you want to use a GD and a 1:1 transfer thus omitting the scx transmission right? This will lower your gear ratio from 16.12 (stock) to 2.5 (GD+transfer) and your scx will become almost six times faster. Rocket scaler!

[FireWire79]

Awesome. You got it right now. GD600 and 1:1 t-case. Fortunately I can use the other gear option to take it as low as 3.5. If it really is six times faster than what it was, I may not have to get that 10t Cobalt motor, could be too much power. All I think it would lead to broken shafts and other problems.

[MadForce]

It will be 6.448 times faster to be exact! Keep in mind that torque will fly out the window with this setup. I would try it with a 55T motor at least.