pphaneuf

Any more details on why?

My understanding is that there's a little less wire in a short stack, so it's basically like a "13.25T", with a bit more power, right? In what situation would it possibly be better to run the normal one?!?

liljohn1064

iTrader: (17)

There are at least 6 SpeedMerchant Roadkill 10s in Madison.

TOADYY

iTrader: (6)

Not exactly. The stator is a little shorter which will result in little less torque with higher RPM. Which is what we want for our lightweight pan cars. The wire wrap will still be 13.5T.

Watch video this he shows you the measurement between a short and regular stack motor.

https://www.youtube.com/watch?v=g9LwWAEBX2g

pphaneuf

Yes, what I mean is that since the stator is a bit shorter, it takes a bit less wire to do 13 and a half turns around it.

A bit less torque and more RPM is what I expected, wondering if there's an effect on overall power, or if it's just a different trade-off? I'm guessing there's an effect, because we can just change the rollout to trade RPM for torque already...

liljohn1064

iTrader: (17)

Trade off. It also increases the current the motor pulls.

You were right at the point of saying it: Less turns or shorter stator stack (less wire) is more rpm at a higher current draw. Loss of torque is marginal as brushless has too much anyway. But, it will make the motor feel softer on takeoff. Both work, you just have to move the gearing around to hit the right power band and feel for the track. Most people are too lazy for this and want the magic bullet: Perfect motor, perfect timing, perfect gear ratio and no effort.

pphaneuf

Ah, but higher current at equal voltage is more watts: more power!

That's also how a low turn motor is more powerful: it has less absolute torque, but more overall power, you just have to gear down. A 4.5T motor has to be geared at 8.0 (in a touring car), and a 21.5T is able to pull 3.0, but there's no question that it has less overall power, it's not just a trade-off.

howardcano

iTrader: (37)

Not quite. Fewer turns = MORE torque and more RPM, everything else being equal. That's because the stator resistance varies as the square of the turn count; the current therefore varies as the inverse square of the turn count.

Example: If the number of turns is decreased by a factor of two, the resistance will decrease by a factor of four. First, the wire length is halved, cutting the resistance in half. Then the wire cross-sectional area is doubled to fill up the otherwise empty space on the stator. That's half the resistance again, for a factor of four. So the current also increases by a factor of four. Since torque is proportional to ampere*turns, four times the current times half the turns = twice the torque.

pphaneuf

Hmm, that's true, higher RPM even implies a higher stall torque, right?

I'm guessing short stack motors have to have the same gauge of wire (they're used in spec racing, they've got to be maxed out already?), so only a bit less resistance, which means more power, but does the shorter stator reduce the field strength?

In short, if short stacks are so good, they'd just make the short stack version, and not bother with the regular one, so seems like there must be a compromise... Since we can readily trade torque for speed with gearing, it feels like I'm missing something...

pphaneuf

Oh, there's one thing: they must be lighter. With a pan car, that has the motor in the pod, that's good (less unsprung mass).

Even at equal power, that'd be better. Don't see what's "1S" about it, though...

TOADYY

iTrader: (6)

That's correct, short stacks are lighter. If you watch that video link I posted, Nick does a comparison between the Fantom short stack with a regular stack.
He compares, specs, weight, stack measurement, amp draw, RPM and etc.

team_tamale

Roadkill10 ready for testing tomorrow.

30Tooth

iTrader: (1)

Heads up!
Lexan sheets will arrive this week according to seller, hope a couple will come out usable

Learnt so much, still improvements will always be made to the shape of the bodyshell according to feedback. Got a few tricks up the sleeve too.

racerx1920

iTrader: (218)

what size tires is everyone running?

TOADYY

iTrader: (6)

Asphalt: full size/60mm
Carpet: 53mm

pphaneuf

I run up to 55mm indoors for club racing, but yeah, at bigger races, 53mm.