So...how, EXACTLY, do you work out what pinion you need?

[Nitroholic]

It's not a Hyper 7 .... but the diffs are

 

It's a Kyosho Madforce. The diffs are actually the same tooth count and identical sizes. I swapped to Hyper ones as they use a straight cut pinion which is stronger than the Kyosho one. I also have a Trophy Truck running a Hyper front/middle and a narrowed Kyosho Madforce solid rear axle ... which is why I know for sure.

[Nitroholic]

Right....

 

one Quicrun 150A on order, and I have clicked buy on one of those black can lower KV motors.

 

This weekend I will go through my stock of pinions and see what I have and also see if I have an ST spur gear ( 52T)

 

NExt job then, while I wait for delivery of the ESC will be to sort out a cap-pack, Having seen they are about £3 total plus 2 small bits of wire, I will make my own. Should mean verything is ready when the ESC gets here.

[Tug]

Good theory on your past ESC failure, it certainly makes sense. 

 

Yes, definitely start low and gear up gradually. 

[Nitroholic]

The calculator was quite helpful .... puts some actual numbers and science to pinion sizing. Feel happier with that

 

Checked my parts pile..

 

No Hyper ST spur, and not likely to pay the £20 price to swap one.....so I will stick with the 46T Huper 7 one.

 

Have 13,15,18,19,20T pinions in 5mm mod 1, so the 13T will go on the motor and I'll take it from there. I have a 1700Kv 4 pole motor on the way and if I fit that, then I will use a 15T pinion.

[Nitroholic]

Finally got out to test this....

 

Fitted the 1700KV motor and a 15T pinion, which the calculator says should be geared for around 40mph and is a good start point.

 

Running conditions are not ideal, as the local authority has decided that cutting the grass is not important....so I had 4-5" of grass to cope with.

 

Ran a pack and a half through before it started raining, and nothing blew up...which is a good beginning.

 

Temp wise....motor maxed out at 85C on the second pack when I was on my way back and in the worst conditions. On the first pack it had maxed out at 75C.

ESC never got hot, with the base feeling warm, but not hot. Batteries maxed at 39C on a hot day. Centre diff got pretty toasty...but I had been running it flat out for most of the pack.

 

Now.....motor wise, this is hotter than I want to go. It ran perfectly well all the time, but I would expect to kill my motor if I keep doing that to it. Do I go up one tooth on the pinion to lower motor revs a touch and get the temps down?

[Tug]

I would try that, but try to replicate the test conditions as closely as you can. The long grass is a killer, it was long grass that pushed my 520kv motor up to 90C! 

 

Anything below 75C is fine.