Savage BL Conversion
 

I did a BL conversion with my savage using the Kersahw designs gearbox a whiole back (which is ok, but is not ideal). I saw the slipperential while browsing the rcm store. I have a few questions:

Firstly, what pitch/mod gear does it have (mod1?). Also, is it suitable for a high load application such as a MT rather than a buggy?

Yes, it's Mod1 pitch. It can be used in a MT, but in a heavier vehicle, you might want to tighten the slipper a bit more or it'll wear the pads faster.

Ya, that I figured. I really only wanted the slipper for landing jumps. I jsut want to make sure the internal gears (for the diff part) are strong enough for the higher loads associated with the larger, heavier truck.

Also, what is the distance from bearing to bearing, as in the dimension between the bearings, not the outside dimension. I am designing a gearbox for my savage to use this, and need to know how far apart the plates should be. Also, what size bearing are they? In addition, I need to know if it is possible to use the slipperential with the stock drive cups. If not, will the stock savage dig bones work? If not, how might I use the slipperentiual with the savage?

I bet I will also need to use custom length dogbones, so I would like to know how far apart the conter of the cups are (as in the distance from where the eye of one dogbone would sit in the cup to where the eye of the other dogbone would it in the other cup).

Lastly, when will you have more 50t spur gears (for the slipperential, of course) in stock?

Sorry for spamming you with questions, but I am really anxious to get this gearbox designed.

here are some sample pics of my gearbox. It currently consists of 3 parts. A main plate, a "cup" (the shroud basically), and a "dust cover" which is inappropriately named. It is basically a removable portion of the "cup" which makes it easy to set the gear mesh. It is possible to run without the cover, but it risks allowing rocks and other debris into the gearbox, potentially damaging the gears. This is meant for straight up bashing as well as racing with a BL setup in the savage. It will work with any savage tvp, and will put the motor as far forward as possible. PLENTY of space in the rear for batts, including the long 170mm ones (if using either FLM ext. TVP's (what I have) or Xl tvps)

This gearbox is compatible with ratios from 48:9 up to 48:13 or 50:12 (based on distance between the gear shafts).

EDIT: weird tabs on top are a mounting point for a not yet designed ESC mount.

Full album:
http://s437.photobucket.com/albums/q...rbox%20teaser/

with cover:
http://i437.photobucket.com/albums/q...r/isoview1.jpg

without cover:
http://i437.photobucket.com/albums/q...w1_nocover.jpg

other pics:
http://i437.photobucket.com/albums/q...r/isoview2.jpg

http://i437.photobucket.com/albums/q...r/cupview2.jpg

http://i437.photobucket.com/albums/q...r/cupview1.jpg

http://i437.photobucket.com/albums/q...r/cupview3.jpg

http://i437.photobucket.com/albums/q...r/cupview4.jpg

http://i437.photobucket.com/albums/q...r/cupview5.jpg

Wow!! It looks really great and I bet those who intend to put the Slipperential in their Savage might be interested. But I think its going to cost a lot to get this case fabricated..

We are building a slipperential savage. With parts from Mike. If you want I can post some pictures....


cheers

Daf

Daf, please post some pics on what you guys are working on. Extremely interested to see what Mike has to offer to the savage owners.

Will do! As soon as I get the chance to upload some pics, maybe tomorrow night.

You can sign me up to buy one of those if they get made, nice design!

Ya, I'd be interested in seeing what you guys are coming up with too. Proly be a lot cheaper too, lol. I had 2 main goals for this box: 1) have the gearobx/motor as far forward as possible and 2) have the gears sealed so devris doesn't damage them.

Third less important goal was low CG

EDIT: I lied, I actually had 3 main goals. THe thrid was to make it machinist friendly. It is designed so that it can be meilled on any 3-axis mill without the use of any soft jaws (becasue there is a good chance I may be machining it myself at the techshop, and if I am not, it will proabbly reduce fab costs). It has parrallel sides so its can be viced up easily. Low cg is 4th, less important goal.

EDIT 2: TO admin (or another knowlegable person): I still need to know the distance between the bearings. I also need to the distance from the bearing to the slipper adjustment so I can make a opeining in the case for the tool to fit through. Also want to know if the stock cups will work with stock savage dog bones, as well as waht there diameter is.

Hey Spiffy, I like the enclosed box idea. Doing this would also allow you to lubricate the gears with something, which will also help wear. Not sure if you could run the slipperential in an oil bath due to the pad design, but some dr lube or grease would work ok.

As for the little removable cover, you could make that out of something clear like plexi/polycarbonate. That way you could check the mesh without removing it.

Just to verify - you have designed it to hand the make gearing of 12/50? What diameter motor did you design around? I see that you have the motor mount face recessed into the plate, could it be designed to have the mount area flush with the face of the casing? That way different diameter motors could be used? I know that there is only so much space between the tvps on the savage, and I am sure your design takes that into account.

Very interesting, I would like something similar to this for my savage!

Jut did some math, and you may have some motor clearance issues with the 46/9 gearing. The diff output diameter is something like 15+mm. Depending on the diameter of motor used it may contact the diff output when smaller pinions are used...

Hey Daf! that would be great. I was planning on a CD/Slipdiff Savage too, but I don't have the time and tools to get it all done properly in any time soon (may or may not have seen my thread.)

Question tho, are you planning on a direct drive unit, or some sort of gear reduction (ie a one spd tranny, like some of the first version slipperentials?)

That was a big stumbling block I was running into. A big spur hangs out the bottom or has to have unfriendly driveline angles (for high mounting.) Likewise, a small spur fits nicer, but offers little gear reduction, even with a small pinion. EG, w/ a 10T pinion & 46T spur, on the stock diffs you only get a ~15.9:1 FDR. Not much if you have a heavy savage and big 40 series tires.
Forget about running the Cen diffs w/ their 2.89 ratio. G/L, I hope to see what you come up with.

Wait, ur saying it comes with a 46t spur, not a 48t.... SNAP. I have it setup for use with the neu-castle finned motors (42mm diamter), but the diamter is actually less than that up front at the end bell. I don't remember what diamter I made it, but it is the right diamter for the front of the castle motors. I hadn't orgianlyl desgined it to sell... BUT, if there is enough interest, and my design ends up being much different than mikes, then I may sell them. Let's see what mike has to offer first though.

I did the math,and with the neu-castle motor, the closest mesh you can get is one with 48:9, not 46:9. 46:9 is a tad high for the savage anyways. In fact, 48:9 is a tad high too. 50:9 and 50:10 are ideal ratios.

If I do decide to sell these, I will be fabricating them at the techshop, as it is too expensive for mew to have someone else fabricate them if I sell them (i.e., I have to mark up the marked up price, which will make it insanely expensive). If I fab them myself, I can sell them at a reasonable price. Also, I can change individual ones for different motors and hole patterns, as only the main plat would have to change. The "cup" part would be the same for all of them.

Another cool feature I didn't mention is that the screw hole for mounting the motor is completely counterbored, and the cup goes on top, leaving enough space for your allen wrench, but not allowing the screws to fall out. This means you can easily remove the motor and put it back in without having to reseat the screws. This makes changing motors and pinions easy while leaving the gearbox in the truck.
I don't know if that makes sense, so if it doesn't I'll try and get soem pics of it.

EDIT: It can handle 50:12. An easy way to see if the gearing will work is 48:9 + 6 teeth anywhere. (you can add 2 to one side, and 1 to the other, or 3 to one side, and none to the other). Mod 1 gearing works out such that increasing either the pinion or spur by 1 tooth will increase the distance between the shafts by .5 mm (it increases the mesh diamter of that gear by 1mm). I have my ratios set as follows. Based off the distance for 48:9, you can go in an additional 1.5mm (on only one side, so a total shoaft movement of .75). Round 1.5 down to 1, for a 1 tooth reduction, (but the motor may interfere with the cup). You can go out an addition 6.5mm (shaft movement of 3.25mm), so round 6.5mm down to 6 for 6 additional teeth possible (You will still have about 1mm between the motor and chassis if the motor is ALL the way out to 6.5mm, which it never will be, because it won't be in mesh with anything there.

I made a typo above, which I will fix. The max distance is with 50:13 or 48:15 (both of which are WAYYY too high for a savage). Basically, although I didnt have intentions of selling, I kept speed demons in mind jsut in case I do decide to sell.

The savage with 40 series wheels, CEN diffs, and 50:9 slipperenital/pinion garing yield about the same reduction as the stock flux with the stock 44:25 gearing

Hmm, good info.

Given your info, it looks like your design will handle 46/16 gearing. Since you have designed it to fit the neu/castle motor, it will fit a smooth can neu just fine. I have a special project that will use a 1527 2y motor (625kv) on 10s lipo, which makes for low motor rpms.

I was going to lock the X tranny locked in second gear, and use 47/23 gearing, but I am not sure if the tranny can handle it. That motor can make some torque, and the vehicle will not be light. Not sure if I would use a std diff, or Mike's slipperential.

As for your question on the bearing to bearing dimension, it should be the same as a losi 8 diff (I think that is the diff with the smallest spacing). Mike made the diff to fit most 8th buggies, and it requires shimming between the bearings and the bulkheads to fit some of the brands. I would make yours to fit a std hotbodies/ofna/kyosho diff, and the slipperential will fit (may need shimming) and will alos allow the largest number of available diffs to fit. I would most likely use a hpi al diff cup with a kyosho plastic spur, as the plastic will provide some shock protection, and run a bit cooler than steel on steel. And I could grease it since your design is sealed.

My other question is are you using stock chassis holes to mount it? Or do you plan to drill the chassis? Either is fine with me, as I would make my own tvps...

It is currently designed to use the stock tvp mounting holes. HOwever, a neu 1527 is too long and won't fit in the space alotted. I currently have mounting holes to have it mount at the front 2 holes of the stock transmission mounting holes. I can make a second set of holes to have it mount in the 2 rear which would allow you to use the neu 1527, but it would also limit battery space.

To give you an idea of the size of the gearbox, the entire thing sits inside the TVP. Nothing hangs over the side, sticks out the bottom, or even the top, so its pretty small. Smaller than even the kershaw designs DD gearbox. The whole thing is smaller than the stock savage tranny.

EDIT: also, what is the distance between bearings on the standard hotbodies/ofna/kyosho diffs?

I will pull the center diff out of my hyper8 and let you know, you want the dimesion from the inside of the bearings? Or the out side? I will give you both. Do you prefer inches or metric? My dial calipers do inch, the mertic ones walked off one day...!!!

I planned to mount the setup where the stock tranny is and place the motor pointing towards the back of the truck. Batteries would be in front. This truck will have a 23" wb (long) so I plenty of room. Planned to use the savage xl rear driveshaft in the rear and a custom length shaft in front.

The diff cups that come on the slipperential should fit the stock savage center driveshafts. Most of those dogbones are the smae size on the ends.

I can say that the savage xl have larger ball ends on the wheel shafts than the center shafts have. I have used the lst and muggy center driveshafts and the lst1 wheels driveshafts as center drives. They have a cvd end with 8mm hole, so they work with the savage pinion gears. The dogbone end fits the savage output cups on the tranny, and most center diff cups too. 1/8 scale buggys and truggys are mostly standardized on the dogbone end size.

I can't see your pix here, but I'm excited to see them later, sry for the hijack :)

When you say 44:25, are you talking spur/pinion? or the internal tranny gears? I assume the former, which is still quite low (~16:1), but workable. Only bad part would be the rapid wear on such a sm pinion. G/L

I was talking about the spur pinion. The flux stock with 44:25 spur:pinoin is about the same as Big joes, Cen diffs, and 50:9 (slipperential pinion) ratio.

Here´s the slipperental savage build
http://rc-dc.ch/gallery/thumbnails.php?album=35
stay tuned

it's not sealed :(. Any word on the dimension between the bearings?

Not enclosed is no issue, just look at truggies and stuff.

Distance between bearings is just like xray, mugen etc diffs. I can measure it up tonight if you want.

I don't have any truggies, so I can't measure the distance, so if someone could do that, it would be greatly appreciated.

About being sealed, there is a large difference between truggies and a savage. To start, most truggies have a chassis with no holes on the bottom, and the body covers most of the openings. I have a buggy, and there is about a 1/8" gap between the body and the chassis. Very little dirt gets in. On the other hand, the savage chassis is completely open, and the body barely protects it at all. Many people (such as my self) run without a body (I have a nylon rollcage instead). This means there is absolutely nothing protecting the gears from larger debris. If even a small rock interferes with the gears, it will cause a lot of damage. In addition, running sealed allows you to lubricate better, for less overall wear on the gears. Therefore, I want a sealed gearbox on my savage.

huh, every truggy I have seen has a hole for the spur gear... and this savage has a skidplate with no holes.

trust me, enclosures are not needed. (Remember the MadForce/Twinforce and many other trucks?)
We had a center diff savage like that before, no issues whatsoever, still running stong, with bashing in gravel pits and everything.
It's completly sealed from below anyway, and some lexan sheets behind the TVPs would complete the job...

A direct drive pinion to spur needs no lubrication.

But to each his own

Daf

Hey, the spur/pinion is always open, and that's everything there is anyway, no transmission as such...

I agree with Dafni, I have run open mod1 spur /pinion on a Gmaxx transmission without problems for over two years.

Dafni, I'm not fond of the losi shocks on there (make it look too bulky for my tatse) but very nice setup, on the level of your revo setups

Is there a downside to sealing it up? I cannot think of any reason to not seal it up, and the lack or debris will add to the gears lifespan.

While a direct drive may not require lubrication, it will extend the life of the gears... And lube usually keeps stuff cooler, which is always good.

Access to the center diff may be more difficult, but once you have it set correctly it is not really necessary to get to it.

You would not consider running the ring/pinion without lubrication...

I don't think there is any downside other than increased mass, but then again, we are talking abou brushless here. Increased mass near the front means more traction, which means you can put down more power.

Regardless, I guess this is a thing of what the ed user likes best. I like sealed better, some others might like open better for the weigt savings.

Any word on the distance between bearings on a standard center diff?

BTW: My gerbox is currently less than 200grams, and still has plenty of room to reduce that more. I am going to wait till I have final dimensions before I really lean it out though.

Bearing distance on XRay/Mugen/Slipperential Diff: 32.5mm (32.3 on xray?)

Ok, measured the diff and it is 34mm from the outside of the bearing to outside of the other bearing. That is a hyper8 diff with a plastic kyosho spur, so it should be the widest spur/cup combo you will encounter. Any slack can be taken up with 16mm od shims.

Thanks. I have updated my CAD to accept a max bearing to bearing (outside) dimension of 34.3mm. The total mass now is about 218.6grams with room to reduce mass if neccesary.

Anybody know how far the slipper adjustment hole is from either of the bearings. I would like to add an opening to adjust the slipper without taking apart the truck. (kind of like the shift adjustment on the stock savage)

Changed my minf. I made the outside dimension 32.6, I don't think I will be using the hyper8 diff if there are other diffs that do the same thing in a smaller size. Unless, of course, there is a reason that the hyper8 diff is somehow superior. Is it?

UPDATE:
Now that school is out, I have more time to work on this project (at least for a couple weeks until my internship begins).

So, getting these made via CNC mill from aluminum will be VERY expensive. But who cares if its made from aluminum. I mean, its a tranny, and as far as the chassis is concerned, it does little to strengthen the vehicle. (which is why no one really uses the few avaible alum trannies for the savage)

I have access to a rapid prototyping machine that is much more practical.

I will be churning out one two for myself this coming week. I am wondering if anybody would be interested in a plastic version. A few changes may be made to the design you see now, but overall, it will be the same. Instead of tapping the holes, i will make holes ready to be tapped, but since its plastic, I will let the screw thread itself in. Machine screws will work fine, plastic screws are not neccesary. (I have always found the machine screws to be more snug than actual plastic screws anyways.)

Also, since rapid protoype makes it easier to do curves (like things curved in multiple dimensions), I may add some extra stuff (or remove) to make assembly easier. I can also easily customize them for different motors/pinion sizes if needed.

For low kv motors, I may offer a version that sits the motor a tad higher (like .125" or .25") to allow larger pinions (15+ teeth)

Sounds good to me, I would be interested in one to try in my 5th scale savage. Pm me a price...

Also, to anyone interested, please understand these 2 things:
1) You will need to get ahold of your own custom length dogbones (as the output shaft is offcenter, and the gearbox is narrower than stock).
2) It is HIGHLY reccomendded that one use a skid plate under this. WHY? I designed this for my FLM tvp with skid plate, and I made the bottom pretty thin near where the spur goes in order to keep CG low as possible. (I may or may not make a version with a thick bottom for people not using skid plates)

UPDATE:
cahnged the parameters in the CAD to reflect the change in material. The new mass of the gearbox itself is approximately 102grams not including hardware (screws, etc). This mass also includes the included ESC deck.

UPDATED PICS ADDED: HEre is a newer version of the gearbox including fillets since it will be made from plastic. THe deck you see on top is for mounting a CC Mamba MOnster. It has slots for zip ties built in. The deck is removable, and other versions for larger ESC's can be made.

http://i437.photobucket.com/albums/q...uctionABS2.jpg

http://i437.photobucket.com/albums/q...ructionABS.jpg

Based on FLM tvp's, so the motor/ esc deck will end up where the stock reciever box goes. If you want to keep the recieevr box, you can drill new mountin holes and mount it the other way (so the motor is at the rear).

Cool looking tranny. I understand that some people want the gearbox enclosed, but there really is no need to do it - and any lube you think you may put on the gears will fly off regardless of if there is an enclosure or not. One huge advantage of an open gearbox when using the slipperential is the ability to adjust the slipper without taking it all apart to get to the adjustment nut. Another possible advantage I can think of is the occasional situation where the pinion set screw loosens. It can loosen to the point of actually coming out of the pinion - in an open design, it just flies away. In the closed box, it is likely to get into the gear mesh and cause carnage.
Also, I think the prototype will be fine with the rapid prototyping, but the motor has some weight, and there will be a substantial amount of torque on the assembly as the motor generates the needed power - aluminum is probably the best bet for a rigid tranny and sound gear mesh. Looks to be a cool project and I am excited to see it completed. :)

About the pinion getting loose, generally, the set screw gets loose enought that the pinion doesn't spin with the motor, and then still has to back out quite a few turns before coming loose. I don't see how it would go flying out. ALso, I was going to have holes on the final version for adjustments.

Secondly, I called the shop today, and found out they charge $50 per cubic inch printed, so its much too expensive. Im getting quotes for cnc milling 6061-t6 alum from some other places.

You guys have a lot of custom made stuff, but i wasn't sure if you did machining in house. If you do, let me know, maybe I can get a quote?

EDIT: Also about the lube flying off. I made the circle around the spur only 1 mm from the spur itself, so once could put a bunch of low viscosity lubricant at the bottom , so even if it flies off, it will pick more up at the bottom. Kinda lke the oil pan in a car. I kept assembly in mind as well, so you can add oil without dissassembling it. ALso, if you look at the other thread, you will notice there is a removable cover over the pinion for setting the mesh easily.

I don't like open for bashing because if you are jsut drifting around in dirt i think soem of the rock could damage the gears. I konw there is dirt on the gears on my kershaw gearbox, and even if it doens't shred immediately, it definately wears the gears.

If you have a healthy flat spot on the motor shaft(like Castle or neu), the pinion can be quite loose and the motor will still enagage. It can happen and has - just thought I would make mention of it.
All our items start production in house until volume justifies sending it out(or my time). Yes, I could make it, but not very fast, as I am up to my neck in projects at the moment.
Regarding the oil/lube flying off - I would run dry myself, but a sticky lubricant in very small quantitiy would be the most I would suggest. You wouldn't want the main power transmission to have to trudge through any oil at all - it would rob tons of power and generate a lot of motor, esc and battery heat (would have the same affect as oil in the sealed front/rear diff in that it would SLOW DOWN movement). If using the Slipperential, it would serve to defeat the slipper(make it too slippery) anyways, but even a straight diff shouldn't run through liquid on the power side. :)

Well, I wasn't planning to run oil, but my point was if someone wanted to, they could. Also, i meant a very little amount of low weight oil. Like only enough so the tips of the gear teeth would touch it. no so much that it is submerged.
My main reason for runninng sealed is the dirt. also, it makes mounting easier, since you have more surface to moun to. i.e., i can make it a drop in repalcement. Most center diffs i have seen are mounted to a skid palte, sicne that allows you to drill holes wherever you want.

Also, the pinion can be quite loose and still engage, you are right. But if the set back out to the point where it cannot possible touch the shaft, the set screw is still inside the pinion itself. And would have to back out at least 2 or 3 more turns before it could fall out.
I understand it could happen on rare occasions, but I do not see that happening often enough for it be an issue. The easiest way to explain would be for you to pick up a pinion
and then loosen the set screw until you can no lonher see it through the hole the sahft goes through. (that is how much it would have to back out before it stops engaging, flat or not). Now see how many turns you have to go before it comes out. I jsut dont see that coming out of a stationary pinion.