Direct drive= what turn motor?

[STANG KILLA SS]

ive got a project(2wd) im doing direct drive in, looking for the wheel speed of a stadium truck (ie T4 etc) that has a 20-27 turn motor in it. (no clue what MPH that is)
but i want to do DD, so what turn motor would get me about that same Wheel speed? (with a TLT axle)

[DKNguyen]

You can't really. Motor power peaks when they run at half speed and is efficient when they run at about 1/7th of stall. So to get a "regular" motor that can move your truck directly, it would have be very very very very large with a power rating much much much higher than what you really need. Suppose you could move the truck using motor A and a gear ratio of 30:1, then the motor you need for direct drive would have to be about 30 times bigger than motor A.

Or if you increased the windings, theoretically not accounting for the losses of such a long winding wire, such a motor would need so many windings that the wire would have to be super thin. THat's what gearboxes are for. Even planes can't do direct drive without an outrunner and props spin much faster and need much less torque than wheels. So you need a ginormous motor that will be oversized (like as big as your truck) for the load, or it will need wires so thin that they don't exist at all to make those windings.

But to answer your question theoretically, maybe a 14 pole outrunner that weights 4-6oz and has at least 1000 turns.

EDIT: I don't think the motor above could exist because the torque that the above motor should produce requires magnetic fields that are far too strong and magnetic saturation would kick in well before that. SO the motor would still need to be pretty big.

[CrawlinClodKiller]

http://www.finedesignrc.com/motorslehner.asp

Couple of those could prob do it. But way expensive. Also maybe one of the 4/1 reduction unit from rc4wd that connect to the end of the motor.

[STANG KILLA SS]

hmm i know a couple of guys here have tryed DD...... not looking to go brushless.
i wonder what a 75 turn would do? anyone know the RPMs of a 55, 65, or 75T on a 6 cell battery would do rpm wise?

how about the rpms of the drive cups on a stealth tranny with a stock 27T motor and a average pinion/spur setup.

[DKNguyen]

Maybe I'm thinking of all-metal 15lbs rigs? Still seems to be pushing it in my mind though. When you mean direct drive, you mean zero gearing right? Or do you mean something else?

[JavelinSST390]

You could do it, in theory, but you'd have a slow-accellerating top-speed merchant on your hands. It would have UNGODLY top end, but would take FOREVER to get there. I'm assuming you want to hook the output of a motor directly to a driveshaft directly to the rear axle? Well, just think in terms of motor top-speed, if the motors top speed is , say 24,000 RPM, and the rear axle ratio is say, 2:1, then 24,000 RPM motor will get you 12,000 RPM at the wheels. (assuming the motor has enough torque to get it to Wide-open-throttle)

Now, I know there's lots of variables I've left out here, but unless you want to go scale land-speed-record racing, I just don't think it would work.

If I were building it, I'd just run like a mamba max and a locked 'pede tranny and then hook that to the axle. Should have more than enough power and speed to make it nearly uncontrollable.

[DKNguyen]

Originally Posted by JavelinSST390

You could do it, in theory, but you'd have a slow-accellerating top-speed merchant on your hands. It would have UNGODLY top end, but would take FOREVER to get there. I'm assuming you want to hook the output of a motor directly to a driveshaft directly to the rear axle? Well, just think in terms of motor top-speed, if the motors top speed is , say 24,000 RPM, and the rear axle ratio is say, 2:1, then 24,000 RPM motor will get you 12,000 RPM at the wheels. (assuming the motor has enough torque to get it to Wide-open-throttle)

Assuming the motor had enough torque to overcome the frictional losses involved (IMHO a very big assumption). Otherwise it'd just sit there. Only the torque left over would go into a very slow acceleration.

[toyofast]

This 2.2 rig has direct drive to the axles. Dual outrunners run to worm gear driven axles. Super slow control and it can really get it AWN when RBGerrish hits the go switch. It's almost too fast.

[Calderwood]

Why not at least run a GRU at the motor?

[hotwheels000]

I think it is leaking electrical fluid

[Rathgar]

stealth tranny for example with a 84/24 spur pionin combo has a final drive ratio of 7.9:1(from chart i found on line) . a stock type 27 turn motor i think spin around 20000 at 7.2 volts not sure if thats freewheel or under load.
20000/7.9=2532 rpms at wheels on a stadium truck.

tlt axle has a 2.73:1 ratio. 2532 rpms X 2.73 = 6913 rpms

seems like a 50 or 45 turn motor will spin that fast.my v11 55 turn was almost 7000 on the little piece of paper.


not sure on torque numbers between a 27 and say a 55 turn.

you making a trophy truck?

i could be full of shit though .just what i was thinking of doing for a future build also.