my new attempt
 

KB 8XL 45mm x 75mm... using a hydra 240A and motor water jacket... 6s2P A123s... Water pump, radiator and fan from a supplier for watercooling PCs... no tranny of center diff... 14 or 24 pinion 60T spur... 40 series tires

I would raise the spur a bit, to get it to chassis level, to protect it from rubbing the ground. Looks good

What water pump did you go with? I've been researching and found a few that look good but none in the price range I want to pay. I like the TCS pump, but I've got no reply from them for a while now so I'm concerned about the quality of their service...

why dont other things run simple gears like this? is it harder on the spur? or what?

I think its all to do with gear ratios & the torque required. For example, an Emaxx tranny gives a truck about a 25:1 reduction ratio, since it needs a lot of torque at the wheels fro weedy 550 motors. Alot of vehicles which just use a centre diff/spur arrangement are generally alot lighter, so donr need so much torque at the wheels; that, or they have a stonking greatbig nitro/BL motor with a low kv rating so not as much speed reduction is required in the form of gearing down. I think....

i would think having no extra gears it would cause more torque..? less things the motor would have to turn... but idk.

i dont know much about gears.

Not exactly. Basically, if you just have a spur & pinion, the smaller the pinion/bigger the spur, the more torque but less speed is generated. With a bigger pinion/smaller spur, more speed & less torque is generated. The torque of the motor remains the same either way, but altering the gear ratios can generate more torque or speed, depending on the application. Few motors have enough torque to directly drive the diffs and wheels of a vehicle, except for some outrunners (see Sike's projects for that stuff). The reason why some motors dont like being over geared, such as the Hvmaxx motors, is because they are to weedy, so more torque is required to turn the wheels = large gear reduction of about 25:1 or more. Some powerful motors like neus are so strong they like to be over geared abit, or at least run a smaller reduction ratio, since if they are 'under worked', they tend to over rev and heat up. Its all good fun it is...

lol i never knew it could all get so complicated!:na:

What pinions do you use with the KB Motors? Don't they have a 6mm shaft?
Thanks for your help! :yes:

They do have a 6mm shaft yeah (that sounds so rude)- visit SDP to custom order/make pinions, very reasonable prices.

If you go to sdp, make sure that you select metric unit on top of the list when you are in the online store. Then go to spur gears and select 6mm for the shaft size. I have an 18 and 20t pinion from them and they are nicely made.

Ah, ok thanks! I was very surprised by the uncommon sizes, until i've seen that they are measured in inches. :lol:

I want to build a drop in brace that will but a truggy center diff in a Revo and operate just like this. Great job getting your idea out and built, elmo. In my head-drawings the BL motor would be mounted dead center above the diff spur to allow for even battery distribution on each side.

I agree... it does look nice... do you feel any flex on that chassis?...

Hey Phraedrus, your idea sounds much like THIS.