Custom Outrunner Setup
 

I thought of this setup for my savage and it looks like it'll work pretty much flawless and it has many positive sides and a few negatives. Plant the outrunner on the savage nitro engine plate with a basic motor mount. Run two center diffs from a buggy/truggy on a custom center chassis mount. Run a dogbone from the outrunner to the 1st diff. The 1st diff powers the 2nd diff which powers the rear/front diffs. Its kinda complicated and some of you may think it is pointless to do all this work for this but I want to try it and see how well it turns out. Keep in mind both center diffs will be locked and will have hardened steel ring gears for added durability. I like this idea because it free's up some space and it puts less stress on the outrunner.

Heres a pic of my idea...

(Key- pink= nitro engine mount, blue= outrunner, silver slab infront of outrunner= motor mount, you probably get the rest...)

http://i301.photobucket.com/albums/n...untitled-1.jpg

It looks like there will be a lot of stress on the dogbone from the motor to the CD, but I suppose of you use a thick enough dogbone it should work fine.

Ya Im looking for super bulky dogbones. I really dont think im gonna have to worry about dogbones snapping, just about them wearing to fast...

The front and rear shafts will be turning in opposite directions, unless you put an "idler" gear in between them.

You could run the shaft from the outrunner to the second (bottom) diff and use the first diff (top) to output to the front and rear diffs.

Why not just eliminate the outrunners dogbone? You could make an end for the motor shaft that plus right into the diff cup. If you "stacked" the diffs one on the other you would clear the rear shaft and still be on the center line of the chassis and not back so far, plus no funky angles to wear out the diff cups.

I like your plan DRKnow. Let me switch up the diagram.

Hey td, how does this setup reduce stress on the diffs?

and the standard center spur gear on 1/8th buggies is 45 mm.. so there is 90mm wide or tall.. it seems like it takes up more space then the outrunner..

Looks like a fun project though

I didnt say it will put less stress on the diffs. Just makes me feel safe running the outrunner this way instead of DD.

why, i dont see what protection this is adding... and i ment the Outrunner not the diffs srry

bb16, I think the idea is to put less stress on the outrunners front bearing. Most outrunners will not have a problem here but why not try it?

I do recall one of the newer rc's having a shaft between the motor and transmission to locate the motor in a better position. Just can't remember what it was.

I have found the best learning to be trial and error, experience is good and you'll never come up with something new if you don't try new things.

I think you're thinking of Tamiya's truggy the Nitrage. The engine has a dogbone that goes right into a drive cup that is kinda "in" the transmission.

http://www.tamiyausa.com/product/ite...oduct-id=43532

You will definantly be the first one to do this! If that is why you are doing it then go for t! But imo all of the outrunners you are looking at should handle the strain fine. just mu OPINION. lol

im with pb (wow thats a first Lol) its same load on the same exact load on the motor, maybe more cuz of all the rotational mass... and since both difs are locked ther is no stress reduction.. maybe i miniscule amount cuz there is a drive cup on only one side of the motor

I want to be constructive in my criticism, but I really don't see the point, it's the equivalent of a 46 tooth pinion to center diff setup(assuming 46 tooth cd's) but with added components, extra rotatinal mass and the parasitic power loss of extra parts. Putting a 46 tooth pinion on the outrunner does the same thing, and opens up more room, and costs less, and has less components to fail, and is easier, and makes more sense to me. And why use center diffs if they are locked? That's an awful expensive gear. I'm not trying to bust balls here, but it's like taking the groceries in from the car one item at a time, to my highly sophisticated high school dropout analytical mind anyhoo.:lol:

Guess i beat you to it paralyzed :D

DrKnow is exactly correct. The reason I want low stress on the outrunner is because I dont want the front bearing to blow and because i dont want anything like the grub screws etc popping out while driving. "That wouldnt be a good situation to be in while doing speed runs".

The whole purpose of this project is for less stress on the outrunner. I dont care if their is power loss or anything of that such. I just want a healthy outrunner at all times possible. Plus this is something new and I decided to give it a shot.

You say that u want to save ur motor, but wouldnt running all 1800watts of power through two ends of the shaft.. guessing around 900w on each side.. but with this setscrew u have all the power going through one.

Thats double the stress on the outrunner. Thats what Im trying to eliminate.

d'oh!:lol:

Either %100 stress on one side or %50 on both sides, it's not more stress, adding more components adds more stress, K.I.S.S. Keep it simple silly:lol:

for all the forementioned reasons you are adding stress, I'm not sure on the thinking on this one????????????????????

:whistle:.............. :lol:

you bustin' my balls BL_RVO?:lol:

lol wow, STOP BUSTIN BALLS Rv0! lol

Plausibly... :intello:

I feel as though I should contribute to this thread via a "balls" joke...:mdr:

Anyways, interesting idea Takedown, but I would say it is a bit inefficient as others have said. Inefficiency can lead to more stress sometimes too, so I think your idea may, at the very least, need some tweaking. DrKnow's idea about getting that one drive shaft parallel to the chassis is a start (which I see you noticed and are considering his suggestion).

Something about two center diffs that are locked just doesn't seem like a good idea either. Maybe you should just use two spur gears to achieve the same effect but with far less rotational mass?

here are some constructive links...

First sikes outrunner e-maxx http://www.rc-monster.com/forum/showthread.php?t=9493 A real good guy to follow if you are looking into an outrunner. He's played with Direct drive revo's and outrunners galore. He even has hand wound an outrunner to make it perform better.

A link to the tamiya (thanks to five-oh-joe) http://http://www.tamiyausa.com/product/item.php?product-id=43532 a good demonstration of how-to.

You guys should offer advise, but keep it constructive and positive. Takedown is obveously a thinker, he's come here and thrown out an idea, asked for help with it, and even drawn us a diagram of the parts so we can see what he's saying. He could have come to some good conclusions on his own given the time and the encouragement. Every successful inventor has built on an idea that failed and was evaluated as to why. More attempts were made and failed again. The process repeated until the awnser was found, then it was something to behold.

That said, there is merit to only using one end of the outrunner, you eliminate the torsion of having the front end inertia fighting the back end inertia. How many outrunners have you seen that actually snapped the output shaft from it's own torque?


I would think that the most stress free outrunner/ center diff setup would be an open center diff with some insanely thick fluid, a pinion gear mounted directly to the outrunner via a slipper clutch, you could add a secondary bearing support on the outer part of the pinion gear shaft, and of course overbuilding and underusing every component. That's me and I may not see something Takedown might. He might throw out something and not see something I do. If we're going to help, we should.

I, personally, would like to drill out the shaft of a large outrunner (mabey an 8mm shaft) so that I could put a 4.5mm shaft through it. I would then put it directly in line between the center diff and the rear end. Connect the motor shaft (8mm with a 5mm hole in it) directly to the diff case (via a slipper) and let the rear diff output go through the 4.5mm shaft to the rear end. The outrunners mass would be low and centered, the center diff would keep the front and rear ends from fighting, and the slipper would keep the gears happy. Use KV and voltage to tune the setup like sikes did with his DDRevo.

Now look at the little blue writing at the bottom of my post to figure out why it's only an idea.

Ok, correct me if I am wrong, but the purpose here is to reduce the load on the bearings and shaft of an outrunner motor?

The gearing will not be used to alter the ratio?

If so I have a much simpler idea to help the bearing stresses on the outrunner. If your outrunner has an 8mm shaft, mount it in the chassis with a std mount from the non rotating end. (just like any direct to diff outrunner would mount.) Then make a pair of bulkheads that fit on either end of the motor, and are mounted to the chassis. Place large bearings in these bulkheads that have an 8mm id to support the shaft of the outrunner. Then just place some sort of outdrive on the shaft and use dogbones to connect with the diffs. Motor is mounted low, no addl gearing to fuss with, less rotating mass, and the shaft is fully supported by the bearings in the bulkeads, not by the outrunner bearings. All the outrunner has to do is fight the rotational torque, and a decent motor mount can handle that. Plus the bearings in the bulkhead can be big, and wide. You may need a longer motor shaft to get everything to fit, but that is easy to find/make.

I believe that the bearings are a concern Linc, I'm thinking he is also concerned about the rotational torque as well. I would think keeping a center diff is important. Looking back to sikes DDRevo it seems that killing diffs was a problem, the motor shaft was not the weak link, the diffs were.

I think sikes nailed it pretty good with the outrunner-maxx (3 diffs and a slipper). Only thing is, no extra support for the outrunner bearings, which seems just fine so far...

I geuss could have just said "essentually putting the rear dogbone through the motor shaft of the outrunner" but there's alot involved.

But its still the samme load on the motor, and if td mounts it correctly Directly inline with the diffs then there will be no extra stress on the diffs

Thats what the diffs are for BB. If you place very heavy diff fluid in both diffs it will somewhat act like a slipper on the 1st diff that the outrunner runs. This will not only save the diffs but it will help me feel safe. Plus you can probably use different ring gear sizes for gearing.

I understand what ur saying, but wont the diff just unload when u abuse i with ur trigger finger? and that will be alot of tuning with diff fluids, why not just make a slipper? it would be a hellova lot less complex too. take a look at the B44's clutch

Unless you lock the first diff, it will just unload and spin the out drive that is not connected to anything (going by your pic I am talking about the top diff)

Using a center diff will help the ft & rr diffs survive. I would just ude a center diff, and the correct size pinion gear directly off the motor shaft. No need to have another diff. If mike brings out the slipperential we will have a great solution as it has a slipper built in. No worries about drivetrain shock with that setup!

Ya linc, I was looking into that and it would be nice to have. When is it suppose to be released? I was also thinking that I could run a 2/1 gear ratio so I could double the 300rpm's coming from the outrunner.

Takedown, have you played with BrianG's speed calculator yet?

As noted, you HAVE to lock the first diff, or else it will just unload on the side that has nothing connected to it. At that point, you may as well be using a spur gear there. There is absolutely no benefit to the added rotational mass of a diff if you have to lock it anyway. You can argue all you want, but there is absolutely no reason to have a diff in that location.

Just tested it out. Heres what I got...

http://i301.photobucket.com/albums/n...avagesetup.jpg

Ok here are some pics of the overall room and the layout of the Low CG HPI chassis... I think this custom setup can be done.

http://i301.photobucket.com/albums/n...U/DSC03988.jpg

http://i301.photobucket.com/albums/n...U/DSC03989.jpg

http://i301.photobucket.com/albums/n...U/DSC03995.jpg

Hey Ryan, i had an idea that u might like... have u thought of running mechanical brakes off the outrunner? It will allow you to run cheaper-Higher voltage plane escs. or it would just take the stress off of you current speed control under braking.

Looking at the chassis (mabey you could set the motor in there just for size reference) I would say using a center diff (you can put heavy fluid in it to keep it from unloading too bad) and a large pinion gear (like sikes O-Maxx) would be the best bet. Later on you could get RCMikes slipperential to replace the center diff and you'd have all the bases covered. I realy liked the idea of a indirect mounted pinion gear (basically what you are doing with the motor-dogbone-2nd diff) to keep the load off the motor bearings, but I'm not sure you have the room to do it?

Mechanical brakes are a good idea too. You could run them on the center diff just like a regular buggy.