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Old 11-18-2008, 09:26 AM   #1
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Default Friction coupling driveshaft

I have this idea in my head about a friction coupling between the female and male pieces of the driveshaft. I envision this implemented for the rear driveshaft. I want to deliver less power to the rear than the front, in cases when climbing steep inclines. It is analogous to a MOA rig w/ two ESC's and the ability to deliver power differently to the front and the rear.

My idea is to use the same principals as a press fit; the more engagement the more torque it can withstand. The engagement would be provided by sliding a female shaft between two male shafts, similiar to creating a dig. Except as engagement increased between the female and the transmission male shaft there would be less slip and more power delivered to the rear axle. At maximum engagement of the two shafts the splines of the two shafts would engage creating a positive engagment and the friction would just be a component of it.

I know there are a ton of creative people on this forum so I'm wondering if anyone has already worked through this idea. How well does it work and do you have any pictures?
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Old 11-18-2008, 09:56 AM   #2
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I think I'm picking up what your laying down. An issue you need to realize is that in order for the suspension to work properly the drive shaft must be free to teliscope. If this movement is not free the crawler will not be able to recover from torque twist. If you want to test this just wrap some plumbers tape around the inside driveshaft and go drive up something steep. When the wheel lifts let off the gas...the front wheel will not drop because the driveshaft won't allow the axel to move relitive to the chassis.

I think an alternitive route might be some kind of slipper clutch type thing mounted off the back of the tranny?? I have had the thought of using two transmitions running off one motor with a slipper clutch on the rear drive tranny. I just haven't had the parts laying around to try it yet.
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Old 11-18-2008, 10:15 AM   #3
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Thanks for the info, you definitly are picking up what i'm saying. The way the driveshaft will still be able to telescope is b/c the female shaft can slide freely over the two male shafts (tranny male shaft and axle male shaft). You are correct that the friction coupling between the tranny male shaft and the famale shaft will inhibit the telescoping between the two. But telescoping between the axle male shaft and the famale shaft will still be able to happen. I like your idea of the plumbers tape as the friction medium, when I get around to building this that could be something I will try.
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Old 11-18-2008, 10:33 AM   #4
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Is this intended as a thing you can actuate with a servo or an always on condition? If servo actuation is not on the menu, I have an idea. This will require some traxxas jato driveshafts #5501 or 5000? I'll double check.<<<<5550>>>>...(I have been using these for some time now) any way these are spline drive and just a bit bigger arround than the axial shafts. My idea is to simply cut the drive shaft off next to the yoke and bolt it back together. this should allow for some slip, yes? Might need some sort of a spring like a slipper clutch. the jato shafts are hollow with a thickened wall near the yoke but hollow all the way through. I will need to look at the direction of rotation, a left hand thread might be in order.

Last edited by nathanschmoekel; 11-19-2008 at 08:21 AM. Reason: Part Number 5550
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Old 11-18-2008, 10:46 AM   #5
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yes i was thinking of a servo to be used to disengage the female and tranny male shaft. I was also thinking of using a sping in conjunction w/ the servo that will provide the engagement. therefore the servo only needs to pull on the female shaft to lessen the engagment (servo mounted on axle). your info is beneficial either way, i'll look at those part numbers.
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Old 11-18-2008, 10:06 PM   #6
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I think the slipper clutch idea is the way to go here. Doing it via driveshaft would be terribly complicated and would probably be inconsistant once it got some wear.

I'm envisioning something like an automotive clutch. Use a strong servo to actuate a fork/throwout bearing to compress/decompress the clutch disk to vary the power output to the rear.
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Old 11-19-2008, 04:37 AM   #7
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A slipper clutch defnitly has the right principals to it. I just can't get my head around how to create it. But the concept is right on, the ability to feather the power to the rear. Would the slipper clutch exist at the axle or tranny side?
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Old 11-19-2008, 05:45 AM   #8
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I like the slipper idea on the rear shaft approach. Now thats outside of the box. With that said I would think you would want the slipper on the rear output of the tranny so that it would not hang up on things down low by the pinion. Plus it would be protected by the chassis and skid plate.
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Old 11-19-2008, 08:40 AM   #9
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I edited my last post to show part number 5550 for those jato driveshafts......Now that I have gone back and looked at them closely with these new thoughts in mind I no longer think them to be better than the stock shafts within the context of my last post. They are however stronger than stock and for $8.00 a pair you can't go wrong. On the plus side they do have a much longer female (outside) shaft side to work with. The male side is so short that any mods that would add length or take up sliding room would not effect function in the least.
**Just a note: to use these shafts you ditch the dust boots and metal pieces they come with and just pop them onto the stock axial yokes.

As for the servo actuated part of this equation...I think now I'm a bit lost, but don't bother explaining ...your time is probably better spent fiddling and posting a few pics as things progress

Last edited by nathanschmoekel; 11-19-2008 at 08:44 AM. Reason: spellcheck :)
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Old 11-20-2008, 03:30 AM   #10
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Look at using more of a band brake or clutch setup... old metal working and wood equipment used them alot and would be easier to make servo actuated.
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Old 11-20-2008, 09:24 AM   #11
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I've not made much progress b/c I'm waiting for some parts to come it to prototype with. But I did discover that if I put some auto vacuum hose over 5mm round stock that it pretty much provides the right amount of friction for a male driveshaft. The 5mm slides into the extra yokes you get w/ the axial kit. The vacuum hose I had laying around when I had to re-run all the vacuum lines in my '87 wagoneer after the engine caught fire.

So now I'm still trying to think of a way of sliding the female shaft between the two male shafts. What I have come up w/ so far is a fork idea. The handle of the fork will be attached to a chassis spacer that can roll. The fork will only be attached w/ one screw to the chassis separator so it can move laterally. The two tines of the fork will straddle the female driveshaft. Maybe there is a groove cut in the female shaft that allows the fork to sit in. Then the servo connects to the fork just above the tines. The servo will push the fork front to back.

Does anyone else have any good ideas?
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Old 11-20-2008, 05:27 PM   #12
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I've had this idea brewing for a little while, but this particular method just popped into my head. The concept is essentially the same as your everyday dig system. But instead of running a dog clutch set up as in the normal way, swap that out for a conical clutch. This will mean that much less effort would be required from the servo to provide full engagement as the two tapers will lock together mechanically with enough pressure and still provide varying degrees of torque transfer relative to servo pressure. It would probably be more compact too that a pressure plate style clutch.
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Old 11-22-2008, 01:06 PM   #13
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Default I found a simple way...no servo activation though.

Here is a frictoin coupling system thats cheep AND easy.
NEEDED: to make one drive shaft..
One set of traxxis driveshaft #5550 ($8.00).
One foot of vinyl tubing 1/2in OD x 3/8in ID from the hardware store
(this is usually used as drain tube for water softners and such) ($1.50)
Tools wise you will need a box cutter/ razor knife or simaler and a NEW BLADE.

Overview: The concept here is to split a shaft in half and use the vinyl tubing as a joiner and slipper. The amount of slip can be tuned by using more or less tubing to adjust the friction. Yes water and dirt may effect performance....You can't have your cake and bla bla bla.

Directions:
(shaft length based on my AX-10 with a 12.4in wheel base and stock tranny position ,adjust length as needed)
*Take your driveshaft off your crawler and pop the yokes off.
*Take the new shafts and remove the metal end pieces and seperate the shafts by removing the rubber boots.
*Next use the knife to cut the yoke end from one of the female shafts(smooth outside) leave as much length as possible. Check the fit of the cut end with a male piece...trim a bit more untill the pieces slide freely.
*Now grab one male (splined outside) and trim off 1/4inch of spline.(or as needed, to allow for full compression of the crawlers suspension)
*Take BOTH MALE ENDS and attach your yokes to them.
*Almost done....Cut the modified female shaft in half, make as straight a cut as possible.
*Now using at least an inch of the vinyl tubing join the female shaft back together and install the shaft on the truck.
Yes you will have a female shaft left over...If you don't like/want the slipper use it to make a solid driveshaft.

An additional thing to consider is adding an internal rod between the male shafts under the female shaft. This will keep the two halves better allinged during torque slip. I used a piece of carbon rod from an old kite...brass rod or something else will work just as well. A sloppy fit is ok we don't want binding here just let it float. Make sure to allow for articulation when sizing the length of this piece.
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Old 11-22-2008, 01:37 PM   #14
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Thumbs up Every interesting study here guy's thank's I will use it

I'll, be fiddling with this,soon ... But, at this time I'm, so ty'd up with family stuff that I have'nt gotten the time to spend sharing & trying to think thru this same kind of Idea stuff that you fella's have been talking about here all this time.. I just seen this now. So, hey, you guy's are really getting this stuff figured out pretty well... And keep it all coming along to so when I do, get back to my workbench and have some time to catch up with you all about this great tread, I'll, see what I can come up with that had alot to do with what you guy's have just told me what to do here on this matter of speaking... gotta run have fun with it. and see if any of you could post a pic' or two as to letting me see first hand as to how you got this to work for you.... Thank you all for this info too....
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Old 11-23-2008, 12:40 PM   #15
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What if you just use a ball diff in the trans? It gives you the same concept and you can adjust the slip. If you want to have a dig just slap a servo on and add a brake to the rear drive shaft. When traxxas and venom release those nice manual locking diffs then you would be able to lock unlock depending on how big the diff is, it may be feasable or not.
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Old 11-24-2008, 09:05 AM   #16
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Correct me if I'm wrong...wouldn't a ball diff just spin spin power to the un-loaded side?

What we are after here is a full power to the front axel ,variable or limited power to the rear axel to keep the crawlers rear end from "pushing under" the truck and twisting/ flipping over backwards. Letting the rear driveshaft slip has a canceling effect on torquetwist which is very desirable.

Those remote lockable diffs are very intriguing...a lockable center diff holds many possibilities.
Un-locking the center diff and employing a braking system on the rear driveshaft instead of a traditional dig is one possibility that comes to mind. Combining a center and rear diff with selectable braking on each rear wheel would probably turn tighter yet AND be easier on driveline parts.

Last edited by nathanschmoekel; 11-24-2008 at 09:21 AM. Reason: on a roll
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Old 11-24-2008, 11:42 AM   #17
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I actually got to working on this this weekend. Nathanschm... I do like the idea of breaking up the female shaft and putting the friction coupling between the two pieces. This would alleviate the pressure the servo would have to use to engage the two male shafts. The current setup I'm playing w/ now is as I described above. The benefits of this set up is that the servo can adjust the amount of friction in the coupling. My next step is to figure out how much friction is needed and if the servo has the strength to overcome it. I need to take a picture of what I have come up so far. Thanks for the ideas everyone, I hope this proves to work as well on the rocks as in our heads ;)
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Old 11-24-2008, 12:23 PM   #18
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Mininature Friction Slip Clutches: (made to attach pulley to output side, but could be adapted)
http://www.rinomechanical.com/pdf/Slip-Clutches_SAS.pdf
http://www.huco.com/products.asp?cat=340
These start at $90 at Mcmaster Carr, page 1017.

There were also electro-mech clutches. Which can be found many places. But they are a NON slip clutch that is either engaged or not.


Nate, you have me thinking about the second trans case with slipper.
Could you use a half of case and bring the rear output shaft of the first trans, into where the motor mounts on the second trans through a bearing block you machine up from delrin. But how do you keep the 1:1 ratio? Smallest tooth count I have seen on a trans with slipper clutch is +/-46T.

hmmmmm

Last edited by sweli; 11-24-2008 at 01:33 PM.
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Old 11-24-2008, 08:43 PM   #19
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I tested out the friction coupling driveshaft and I'm doubtful it's going to work. Because the gearing is so high in the axle the driveshaft is under a lot of torque. I became to appreciate this first hand. I didn't hook up the servo or any linkage. I wanted to test the theory by constructing the driveshaft and manualy manipulating the female portion to generate friction; the more the female piece overlapped the rubber sleeve the more friction there was. I used an incline test to assess whether I had enough friction to drive the car up the ramp. I just couldn't generate enough friction to get the car up the incline. I had so much friction that at one point I was using pliers and some strength to slide the female piece over the rubber sleeve. But it just wasn't enough, the car would not go up the incline. Not to mention, I don't think there ever will be a servo strong enough to slide the female piece to apply that much friction.

I think the theory of manipulating the power to the rear would definitely help climb steeper inclines, I just don't think connecting a driveshaft w/ a friction coupling will accomplish it.

So I'm pretty sure this won't work. Anyone else have any other good ideas?
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Old 11-24-2008, 11:25 PM   #20
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What about one of those torque converter setups with the metalic fluid that freezes up or gets thicker under a magnetic field. I heard about those on daily planet once, and it doesnt seem too hard to do, iron filings and some 100K diff oil.

Or even for just a slipper action, a small diff w/ very thick oil.
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