4wd Corr/Pro-4 Truck REDESIGN POSTED 12/23/09 - Page 6 - RC-Monster Forums

12.13.2008, 11:14 PM

Scorpion motors are amazing! Super super nice motors, well known in the heli/plane world

AWESOME build! I love it!

lincpimp · 12.14.2008, 04:10 AM

I like the bearing supported can. From what I have heard the scorpion motors are really nice... I have had good success with axi motors, but may have to try the scorpion out too!

MetalMan · 12.14.2008, 01:30 PM

Last night I was trying to get the motor shaft out of the rear endbell, which is a super tight fit (a lot tighter than the KMS motor). The rear endbell popped off rather easily when I hit the other end of the motor shaft. This was rather fortunate because it allowed me to extract the motor shaft from the endbell with less overall effort. Now it is time to carve the motor shaft into a desirable shape.

12.15.2008, 01:49 AM

ok, sorry for being such a noob but......

why can you direct drive a outrunner but not a inrunner? Wouldnt the motor be significantly over stressed? Why did you choose an outrunner over the inrunner....

again... i apologize in advance

MetalMan · 12.15.2008, 02:18 AM

Don't apologize, we're all here for a good reason! And that reason is to receive comments, ask questions, show off, etc.

In this application outrunners are easy to use because their shafts are removable, and thus easy to modify. We need to somehow get driveshafts or drivecups onto the ends of the motor, and traditional inrunners have the shaft exiting only one side of the motor. That means inrunners require some sort of (reduction) unit that can send power to the front and rear. This unit adds weight and complexity and reduces available space.

If I were to ask a company like Medusa or Neu to build me a custom inrunner with a kv of about 750 and a shaft with appropriate connections on both ends of the motor I would have to dish out a lot more cash than I can afford. Also keep in mind that these motors are 4pole, so compared to 12pole outrunners they might provide less back-emf at startup , potentially making them more prone to severe cogging. Outrunners are much more friendly to user-rewinding as well, so I can always use heavier gauge wire and have a higher total copper fill than what factories put on their outrunners (to make them handle more power).

The KMS was definitely overstressed, as is evident in the pictures. A comparably sized inrunner to that KMS would weigh about twice as much, meaning it would have more copper and a higher current capacity. This Scorpion motor I got is nearly 100grams heavier than the KMS, and has A LOT more copper and is also better built. Hopefully it won't be too heavily stressed.

lincpimp · 12.15.2008, 02:25 AM

Quote:

Originally Posted by Andrew32

ok, sorry for being such a noob but......

why can you direct drive a outrunner but not a inrunner? Wouldnt the motor be significantly over stressed? Why did you choose an outrunner over the inrunner....

again... i apologize in advance

The two designs are radically different. An inrunner is better suited to higher rpms, has a lower pole count, and thus does not require the esc to "fire" as many times per rotation. Most escs are limited to the number of times they can fire, so most cars will use an inrunner coupled to a grear reduction device (trans and/or diff) to produce more torque. The stator is light weight, and drive is taken off the center shaft.

An outrunner usually has more than 8 poles, and more rotating mass. They are spun at a slower rpm, and are generally used to direct drive airplane props. They require the esc to fire many times during one rotation, and thus have a lower max rpm, somewhere arounf 20k rpm for most 28-42 sizes. Drive is taken off the outer can or the center shaft, which is bearing supported at one end. They make more torque, but spin slower, so they have a different gearing requirement than an inrunner.

Inrunners will always be more popular for conversions as their operating speeds are very similar to the nitro engine so similar gearing can be used. 4 pole designs like the neu come closer to providing more torque while still retaining the higher operating speeds, and lightweight rotating components.

12.16.2008, 06:00 PM

sweet, learn something new every day

brushlessboy16 · 04.02.2009, 05:18 PM

Any Updates?

SpeedAssault · 04.10.2009, 04:56 PM

I have a few words for ya

1- GREAT Write up !
2- Great build with pics-n-info
3- Great looking Baja

its me · 04.11.2009, 06:05 PM

Wow I missed this one metalman, thing looks sick man!! I love it!

MetalMan · 04.12.2009, 02:20 PM

Thanks guys!

Much has happened with this truck. For starters, it got a rear sway bar a while back, with a design similar to what is used in CORR trucks.
After repeated use the screw holding the lower links to the chassis (can't see it 'cuz it's hidden by the blue spacers) would bend. So I built a beefy lower link mount.
I messed around with the suspension a bit, mainly just the rear suspension, and now it's riding on XTM white springs and I think 15wt. oil. Up front I swapped the shocks to Traxxas Big Bores with Trinity blue springs (cut down) and around 45-50wt. oil.

The body was painted, and now has begun to fall apart. Let's just say this truck LIKES to roll. However, a coworker of mine who is a great driver suggested I lose the rear swaybar because of oversteer, so this is definitely contributing to some of the body roll.

It's kinda sad that I haven't driven this truck in a good month or so, to work on improving its capabilities. Besides, I've got a belt-drive truggy conversion that has been taking up most of my RC time

MetalMan · **HUGE Redesign/Rebuild -** 12.23.2009, 06:17 PM

Hey all,
This truck underwent an entire rebuild of the chassis, where the CG was dropped significantly. Instead of an outrunner it now has a Medusa 36-60-1600 (from my Jammin' X1-CRT) and a slipper clutch using a MT2 slipper shaft and Revo slipper clutch components. With the redesign the driveshaft angles are much better and the lower link mounting is a lot stronger.

I had already driven it but decided it would be a good idea to tear it down and do a little cleaning, so here are the build pictures:

MetalMan · 12.23.2009, 06:17 PM

And some overall shots:

On pavement it still traction rolls quite a bit. Might need to lose the rear sway bar and invest in a front one.

suicideneil · 12.23.2009, 08:54 PM

Does look somewhat lower/ flatter/ whatever than the previous version.

Q. how tough is that lexan? for making parts like that, cant help thinking it might be brittle and snap if flexed too much?..

12.23.2009, 10:06 PM

Quote:

Originally Posted by suicideneil

Does look somewhat lower/ flatter/ whatever than the previous version.

Q. how tough is that lexan? for making parts like that, cant help thinking it might be brittle and snap if flexed too much?..

with the load being applied on the smaller/thinner faces and not applied on the larger faces. it'll take a HUGE load to snap it. (i hope you can understand this cuz i cant explain it haha)