Outrunner to diff in SCX10 - RC-Monster Forums

TexasSP · **Outrunner to diff in SCX10 -** 01.29.2011, 04:28 PM

I am thinking of doing a straight to diff outrunner in an SCX10.

I want to keep COG low which is one reason, and to eliminate the trans is the other. I will also mount battery plates on either side of it. I actually think I can keep everything down low if I do it right.

I will be using a mamba pro and really not set on voltage yet.

I want good low speed driving but be able to get up to 15 mph or so too.

Anyone with outrunner experience have any suggestions on what motor. I don't want anything too expensive either.

I will custom make my own mount from aluminum.

lincpimp · 01.29.2011, 07:16 PM

We need diff ratios, tire size and pick a voltage. Only looking to go 15mph? 3s would be fine for that, but if you have a pack laying around we can just tailor the motor choice to the voltage you have. MMpro can do up to 6s.

TexasSP · 01.29.2011, 10:37 PM

Tire size 4.2-4.5 inches depending on what I go with. Diff ratio is different for front and rear since front is over driven. 36/14 front and 38/13 rear. It can go faster, and I can do 3-6s as I have the packs for that. Already have the pro which is why I am going with it.

jhautz · 01.29.2011, 11:58 PM

If the front and rear dif ratios are different you are gonna need to keep the center dif somewhere in the equation. Replacing the center dif with the solid center shaft of an outrunner you are gonna be scrubbing tires just to drive straight. The reason that an overdriven front dif works is because the center diff absorbs the ratio difference.

07:23 AM

I have nothing to add to the outrunner side of things sorry. But just to clarify for jhautz, crawlers run no true 'diffs'. I.E if you move one tire every other tire moves exactly the same amount. The overdrive is used to help torque twist, steering and having the front pull a little keeps the wheels on the ground in steep climbs. At such low speeds in crawlers you don't notice the tire scrub side of things anyway.

Cheers
Kieren

lincpimp · 01.30.2011, 01:18 PM

With the 4.3 inch tire and 4s lipo a 500kv outrunner would give you 35mph.

In order for you to do this you need to settle on a diff ratio, and tire size. What is the overall weight of the truck? Given startup loads I would almost go with 5s lipo and the lowest kv motor you can get away with.

TexasSP · 01.30.2011, 03:00 PM

The front is overdriven on purpose and will stay that way. It eliminates torques twist, eliminates rear bounce when climbing, and helps with downhill driving. I am not so much worried about finding KV as much as finding the correct outrunner size as I am not as familiar with those.

It is extremely common for scale trucks and crawlers to overdrive the front and their never was nor will be a center diff as that would sacrifice performance.

sikeston34m · 02.01.2011, 04:20 PM

Hi TexasSP,

I got your PM. Interesting thing you are working on putting together here.

When I first looked at the truck, I thought, this is going to be easy. But then I realized you intend to eliminate the transmission.

If you were going to retain the transmission, I would go with an outrunner like this one.:

http://www.hobbyking.com/hobbyking/s...idProduct=9764

I'm pretty sure this one is 8 pole. Tremendous Amount of Torque. I've ran this in the E Revo and in the E maxx. It is 550 size. 37mm X 56mm

If you want to consider trying this motor with your transmission. Gear it low, put it on 6S, and engage 100% drag Brake on your MMPro for the ultimate crawling experience. I feel it would crawl great, plus produce some good top speed when flat running.

Now to eliminate the transmission and recommend a good motor, there are a few things I need to know.

I need the diameter and length of the output shaft on the transmission. We gotta try to match something up with that data.

Then allow some length for your motor mount.

Interesting setup and idea. I look forward to seeing how this evolves.

Hmmmmm........battery? Your compartment will house 1 6-cell nimh pack?

I wouldn't rule out 6S operation. It will be a little taller than a 6-cell nimh pack, but I would consider something like a 6S 2650mah lipo.

Linc is right. Go low on the kv and up the voltage for this setup.

lincpimp · 02.01.2011, 05:31 PM

I missed that this is a crawler.

I understand the different diff ratios now. For some reason I thought this was a short course truck!!!

Any 28 series outrunner should do well.

TexasSP · 02.01.2011, 07:20 PM

Quote:

Originally Posted by sikeston34m

Hi TexasSP,

I got your PM. Interesting thing you are working on putting together here.

When I first looked at the truck, I thought, this is going to be easy. But then I realized you intend to eliminate the transmission.

If you were going to retain the transmission, I would go with an outrunner like this one.:

http://www.hobbyking.com/hobbyking/s...idProduct=9764

I'm pretty sure this one is 8 pole. Tremendous Amount of Torque. I've ran this in the E Revo and in the E maxx. It is 550 size. 37mm X 56mm

If you want to consider trying this motor with your transmission. Gear it low, put it on 6S, and engage 100% drag Brake on your MMPro for the ultimate crawling experience. I feel it would crawl great, plus produce some good top speed when flat running.

Now to eliminate the transmission and recommend a good motor, there are a few things I need to know.

I need the diameter and length of the output shaft on the transmission. We gotta try to match something up with that data.

Then allow some length for your motor mount.

Interesting setup and idea. I look forward to seeing how this evolves.

Hmmmmm........battery? Your compartment will house 1 6-cell nimh pack?

I wouldn't rule out 6S operation. It will be a little taller than a 6-cell nimh pack, but I would consider something like a 6S 2650mah lipo.

Linc is right. Go low on the kv and up the voltage for this setup.

I want to eliminate the transmission to simplify the layout, lower the CG as much as possible, and create something different.

The chassis layout is scale ladder frame style. There is not a battery compartment just a tray. However, in the middle on the lower part of the chassis there are nerf bars which allow width to mount the batteries. I can easily go 6s so that is not a problem.

The main reason I want a little speed is for areas when that extra wheel speed is necessary like getting out of tight places or jumping a short gap. This will be a speed demon by no means.

The output shafts on the tranny to the shafts for the drive line are 5mm but I can get 6mm cups if the output shaft on the outrunner was that big.

I really appreciate you chiming in on this and helping me. I think it has possibilities.

Quote:

Originally Posted by lincpimp

I missed that this is a crawler.

I understand the different diff ratios now. For some reason I thought this was a short course truck!!!

Any 28 series outrunner should do well.

Aha! Yeah, that would be problematic for SC.

sikeston34m · 02.01.2011, 10:35 PM

Something like this? The one on the right, is an AXI 4120/14 660kv with a custom motor shaft. The motor shaft is actually an output shaft from a E Revo Transmission. So it has both ends for the drive cups. The shaft is 6mm.

How much room do we have to mount the motor?

02.02.2011, 07:51 AM

How'd you get those custom shafts? I'm also interested in picking up one of those motors, and setting up an outrunner. What do you do for debris protection?

TexasSP · 02.02.2011, 12:29 PM

Quote:

Originally Posted by sikeston34m

Something like this? The one on the right, is an AXI 4120/14 660kv with a custom motor shaft. The motor shaft is actually an output shaft from a E Revo Transmission. So it has both ends for the drive cups. The shaft is 6mm.

How much room do we have to mount the motor?

Yeah, something like that. I have a good amount of space for the mount, but will have to measure it to give you an exact.

Good to know on the motor shaft part.