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billyboy
09-22-2006, 09:29 PM
im among other things making a remote control 1/4 scale dune buggy, ive got the chassis and the suspension sorted but im having a little trouble with the rear drive assembly, i was going to make the rear axle in one piece solid form but if there is a simple way round to split the axles it would be a better option, anyone had this problem?

CCWKen
09-22-2006, 09:56 PM
A rear "differential" would certainly aid control when turning. One simple method used by some Karts is to use a slip clutch between the two axle halves. This requires the axle to be supported inboard as well as outboard. Another option would be to just drive one wheel and have the other free wheeling.

Fasttrack
09-22-2006, 10:16 PM
"Another option would be to just drive one wheel and have the other free wheeling."

Billyboy- That's a very easy solution which many karts use; when i first saw a one wheel drive kart i thought it was pretty funky. I didn't have alot of faith in its performance but, to be honest, when i got to building karts, i found that most of my single drive karts handled much better and accelerated better or as well as the ones with differentials...now taking them off-roading is a different matter. But for a r/c vehicle i would think one would be ok...

Otherwise a differential isn't horribly difficult to make. The go-kart ones have a cylinder that houses the four gears. Instead of a ring gear and pinion gear, the sprocket is bolted to the outside of this cylinder so its easier to change. Inside the differential you need one shaft perpindicular to your axles with two bevel gears on it. The bevel gears are free to spin. The shaft, however, sits in a pocket in the cylinder so when the cylinder turns, the shaft turns. Then, meshed to the two gears on the shaft are two bevel gears, one keyed to one axle, the other keyed to the other axle.

And then - its time to test it! ( i stripped the teeth of of three of the gears on the first differential i made...i had a homemade tranny and i slipped from third into reverse...yikes!!)

I assume you already knew all that about the basic construction but you probably had trouble finding a bevel gear. Take a look at ebay and google it - when i was looking for go-kart sized bevel gears all i could find were dinky ones that would be good for r/c cars. Infact i saw some especially for r/c cars! If you need i'll do some poking around and see what i can turn up.

Oh - check out "martin gears" - i think that may have been one of the places that had some small bevel gears in anything from steel to brass to plastic. not sure though...they also make sprockets i think

Millman
09-22-2006, 10:54 PM
FT, I think my wife and I will adopt you! Our grandsons just don't have your common sense. If I had enough work, you would be in business. Hard to find a young guy that's interested in being the best! I think you are going to make it.

S_J_H
09-22-2006, 11:45 PM
You could also try a ball bearing diff which is used in smaller scale RC . Fairly simple to make, easily adjustable and hard to break.
Coming from a drag racing back ground I would do a solid axle and the hell with turning corners. :D

Steve

rsr911
09-23-2006, 12:17 AM
You could also try a ball bearing diff which is used in smaller scale RC . Fairly simple to make, easily adjustable and hard to break.
Coming from a drag racing back ground I would do a solid axle and the hell with turning corners. :D

Steve


LOL, I could "park" my old drag car on an incline just by turning the front wheels all the way to one side or another and lock the steering column!

Anyway, on the dune buggy RC car if you plan to run it in dirt and the like just put a solid axle in. If you really want to get carried away you could make a detroit locker, just need some time and a rotary table.

A.K. Boomer
09-23-2006, 03:18 AM
Stock drive makes some pre-fab diffs that might work and if you dont mind dealing with metric Quality transmissions is who i use for my bike cranks, There gears are great, they are in an annealed state for machining and then you can quench harden yourself and they turn out really good with very little deviation and a super hard skin, if you want a tough differential spyder gear set up dont use just two, build a cross yoke and throw in two more...

Weston Bye
09-23-2006, 08:20 AM
See here:

http://www.sherline.com/tip27.htm

japcas
09-23-2006, 08:35 AM
If you wanted to keep things simple, why not look for a used diff out of a smal lawn tractor and modify it if need be. I'm not sure how big a 1/4 scale buggy is but these diffs aren't very big so it might work.

Evan
09-23-2006, 09:23 AM
How is the machine powered?

topct
09-23-2006, 10:09 AM
Small world. I too am working on such a project. And the differential is part of the problem. It just has to have one.

At first I was going to scale up a ball type out of a smaller car. Not very complicated and as stated, adjustable for slip.

However I wanted to build something that could be put together with as much off the shelf parts as possible so I have decided to go with a small differential made for a small lawn tractor. They have also been used in some of what they call mobility chairs here.

I won't go for suspension at first, just a basic chassis to hold the engine and steering in place until I can be sure of the one thing that might be a problem. The steering.

What to use to steer the thing? Mine might come out a little bigger than 1/4 scale. I'm using wheels and tires from HF here. And I don't think what they are calling 1/4 scale servos (for aircraft) will be strong enough. I am considering two options. 1. using two of the biggest servos Hi Tech makes and gearing them down or 2. there is a way to hack a regular servo to drive a larger geared motor.

For power I have an engine off one of those stand up scooters. They have a very tidy reduction gear/clutch on them that will be easy to adapt.

Good luck, and some pictures would be welcome.

Here's a pic of the differential I'm going to use.

http://www2.northerntool.com/product/35768_35768.htm

I think the carrier is about 4 inches in diameter.

pntrbl
09-23-2006, 10:21 AM
I have one of those Northern Tool diffs I got in an E-Bay deal with some other parts that I'm not planning on using. It's just taking up space. I could be persuaded for next to nothing ....

Bill

topct
09-23-2006, 10:43 AM
pntrbl, check your mail.

billyboy
09-23-2006, 09:37 PM
thanks for the reply's and advice, Argos (general houseware store in england)was selling some real cheap petrol hedge strimmers off for £50 so i couldnt resist buying one just for the engine, when i stripped it all down the engine seems to be the same as a zanoa but is un-named, evan its a 34cc with a built in clutch assy, i did want to buy the FG marder r/c buggy which uses a standard 26cc zanoa engine but at £500+ its a little out of my budget so im having a go at making my own version of the buggy, a few little obsticles to get over first like drives, steering, ect but these shouldnt prove to hard, i like the idea of a northern tool diff and thanks pntrbl but i think i may be able to lay my hands on one, topct these modern high torque servos for scale a/c should perform your needs if just for the steering, ill post some pictures when it starts to take shape.

bill

Fasttrack
09-23-2006, 11:19 PM
Once again, thank you Millman! I was having a bad day until i read that...

Billyboy - post pics when you get a chance! Sounds like an interesting project.

Evan
09-23-2006, 11:35 PM
With that sort of powerplant I would be very tempted to experiment with a torque converter viscous drive. I am thinking of a square tube perhaps 2" OD and a foot long with bearings and seals at each end. The axles are half shafts that meet in the middle at a pair of bearings so the entire thing is self supporting. The tube is driven either by belt pulley or chain sprocket. The axles have grooves machined in them axially, like fins, and almost touch the flat sides of the ID of the square tube. The entire assembly is filled with oil.

When the square tube rotates the oil will follow and transfer energy to the axles individually but equally. It will differentiate as required. It also eliminates any need for a clutch and will allow the engine to run at a more efficient rpm most of the time with no gearing.

darryl
09-24-2006, 12:12 AM
What are you doing for a motor? Here's an idea. Buy two cordless drills and arrange to use them to drive the rear axles separately. Then wire them in series and run them from two of the four batteries you got with the drills. The batteries are also wired in series. You get an automatic differential, the power of two motors running simultaneously, and a spare dual battery pack. You'll need a controller capable of handling the voltage.

Ok, if the cordless drill idea doesn't do it for you, use two motors anyway. Each rear wheel gets it's own motor. You can experiment with wiring them in series or in parallel. Series will get you better differential action, but parallel will get you guaranteed torque at each wheel and still with some differential action. This will be similar to limited slip.

If you're stuck on using a single motor, then you could buy two chinese angle grinders and rob them for the gears. That's enough parts to make up your own differential, and probably about in the right size range. All the ones I've seen have helical gears, so it should make for a nice smooth diff. These things are so cheap now that it might actually cost you less than ordering gears and paying shipping. A bonus is you'll get two high speed ac motors to figure out something to do with. Maybe make a dual head weed eater contraption. :)

Back to the cordless drills- most of these now have planetary gearsets in them. These can also be used to make a differential. I'm sure a google search will turn up an animation or something showing how it's done.

Ok, now I've gone and read your latest post- using a 34cc gas motor. Forget the cordless drill parts, but the angle grinder gears would probably handle that ok.

Evan
09-24-2006, 12:14 AM
Billyboy is using a weed trimmer motor.

IOWOLF
09-24-2006, 07:51 AM
I'm just glad its not another Psyco kart.

LastOldDog
09-24-2006, 06:40 PM
With that sort of powerplant I would be very tempted to experiment with a torque converter viscous drive. I am thinking of a square tube perhaps 2" OD and a foot long with bearings and seals at each end. The axles are half shafts that meet in the middle at a pair of bearings so the entire thing is self supporting. The tube is driven either by belt pulley or chain sprocket. The axles have grooves machined in them axially, like fins, and almost touch the flat sides of the ID of the square tube. The entire assembly is filled with oil.

When the square tube rotates the oil will follow and transfer energy to the axles individually but equally. It will differentiate as required. It also eliminates any need for a clutch and will allow the engine to run at a more efficient rpm most of the time with no gearing.

Evan, is this a good excuse to fill your torque tube with Magneto-Rheological fluid? Near instantanous cycling from near zero torque transmision to near full lock-up. Hmmm.
http://www.lord.com/tabid/3318/Default.aspx

Weston Bye
09-24-2006, 08:08 PM
Evan, is this a good excuse to fill your torque tube with Magneto-Rheological fluid? Near instantanous cycling from near zero torque transmision to near full lock-up. Hmmm.
http://www.lord.com/tabid/3318/Default.aspx

MRF - good idea, but you have to think about modulating it: Outer tube should be non-magnetic, aluminum or brass, inner should be steel. Modulate with a powerful permanent magnet moved closer or farther from tube with servo, or drive an electromagnet with a DC motor driver module. Unless well designed, such a clutch may require as much current as an electric drive motor. (put a generator on your IC engine) Performance of the MRF can be optimized by working the fluid in a narrow gap where the magnetism can be concentrated.

Be aware, that it takes considerable magnetism, whether permanent or electromagnet to lock up the MRF.

The people at the above link sell (give?) demonstrator kits, consisting of two syringes and a coupler, filled with MRF, and a magnet for locking and unlocking the fluid as the plungers of the syringes are pushed back and forth.

kap pullen
09-25-2006, 10:44 AM
The germans in WWII used a differential that consisted of hardened wedges at the end of the war.
I don't remember the details but should be easy enough to build.
Kap

A.K. Boomer
09-25-2006, 12:07 PM
The old 2.4 liter V/6 DOHC fiat Dino's used a unique rear end in these "at the time high perf. vehicles" they were a step better than limited slip, they utilized a standard diff. but had additional "wedge cones" , these cones allowed this rear end to behave opposite of a standard diff. anotherwards, you could have one rear tire on ice and one on the road and the power would get transfered to the one with the MOST resistance, many of rear wheel drive cars will also light up the inside tire with power on around a really tight turn in first or second gear but not the Dino, it puts the power to the outside wheel, pretty cool set up, and much better than a limited slip by a clutch pack or a viscous coupling with one thing to be aware of, if the outer tire does break loose around said turn the inside tire does not have much weight on it so swapping ends can be a factor but this will not happen at any kind of speed to speak of because you simply cant supply that kind of torque to the rear wheels in the higher gear range...

By the way, you guys being machinist and all would have had a lot of apreciation for the connecting rods in that car, for back then they were amazing, every millimeter was machined and polished,
am told that ferrari owned fiat even back then and the Dino was created by Enzo's son (who im pretty sure just happend to be named Dino), if my memory serves me correct Dino bit the dust shortly after, this was not a fiat engine, it was more of a ferrari, The Dino made a very distinctive sound, (besides being so throaty from the three-two barrles and the opened up duel exhaust) The Dino was a DOHC engine that utilized cam chains to drive all four cams (which by the way could be dialed in and individually adjusted to suit wether you wanted the car to have low end or scream all the way up to its redline)
Because all V engines have a staggerd bank (one is more foreward than the other) the Dino ran a single gear from the crank up to a geared shaft that then branched out into two offset sprockets to drive each individual bank,
The thing is is they used straight cut gears to achieve this, you would fire up this little beast and even with all the carb and exhaust music it would also sound like it was running a supercharger, I remember taking that car for a test drive after rebuilding the engine with the top down through the tiny little town of rockvale colo. and you would think i was in a flying saucer with the looks that i got from some of the huckleberries, Sorry fella's, little two much caffiene this morn, but now you know a little about the Dino...

Dr. Rob
09-25-2006, 05:02 PM
Yeah. The go-lever on my milling machine is capped with the gearshifter knob from a '72 Ferrari Dino. (friend had one. Knob is all that remains after he crashed it)

Anyway, about this differential thing... Can you just use whatever solid axle you like, and put a one-way needle roller clutch in either of the back wheels, or both? = overrun clutch.

AK Boomer, re: earlier post, you said something about bike cranks and Quality transmission... pardon me, what?

topct
09-25-2006, 07:14 PM
"Can you just use whatever solid axle you like, and put a one-way needle roller clutch in either of the back wheels, or both? = overrun clutch."

If you put one in each wheel or axle that would just make it a solid axle when driven. It would be pointless to put one on just one wheel/axle.

The wheels/axles need to turn at different speeds when "powered" around a turn.

A.K. Boomer
09-25-2006, 11:22 PM
"Can you just use whatever solid axle you like, and put a one-way needle roller clutch in either of the back wheels, or both? = overrun clutch."

If you put one in each wheel or axle that would just make it a solid axle when driven. It would be pointless to put one on just one wheel/axle.

The wheels/axles need to turn at different speeds when "powered" around a turn.



Hey-Hey wait a minute topct,,, Dr. Rob stated in "one or both" --- if you put an overrun clutch in both rear wheels it would make it a positive drive system in the straights but deliver the power to the inside wheel (slowest moving) in a turn (and allow the outside wheel to "overrun") instead of splitting it up like a regular diff. yet it would have one huge advantage over a regular diff. --- if one wheel is on ice and one on pavement it will deliver the power to the one on pavement -- as we all know the standard diff. chooses the path of least resistance hence the vehicle gets stuck, this may not be the perfect set up (for one there would be no reverse) but this car would not scrubb its tires and wear them out around turns --- it would not exibit solid axle behaviour in this situation,
Dr Rob, quality transmission is based out of New hyde park N.Y. www.qtcgears.com
im R&Ding a more efficient means of transmitting power in a bicycle crank

Those ferrari Dino's are one of the most sexyist looking rides that a vintage car could offer, its a shame your friend stuffed it, I believe the Fiat Dino was also called a "spyder" and although it had some nice lines it no where near the beauty like the Ferrari Dino...

A.K. Boomer
09-26-2006, 12:25 AM
All this talk of diffs and you guys jogged a memory of yesteryear, had a good friend back in michigan were i grew up, he had a duece and a quarta (a buick electra 225) we used to party our arsses off in that thing, one day he gets stuck with one wheel on the pavement and one on glare ice, his method of dealing with this was to mash the accelerator and burn through the ice till you hit dirt or pavement or whatever comes first, this day he was even more impatient than usual so he mashes it and were just sitting there like any other day but its taking longer so i look over at the speedo, and watch it shift out of first into second, no biggie, standard routine, but now its aproaching second gear shift point, no biggie been there done that, but now it shifts out of second into third -- Ok this is getting interesting, we are aproaching 100 mph on the speedo, now its 110, now its 120, then BOOOOOOOM the car drops down about 6 inches on the right rear, we get out and look and heres the rim sitting on the ground with no tire, we all are like --- geeze i know the tire was doing 240 mph but were in the fuqe did it go?, we cant find the tire anywhere, finnaly Bob (my friend) opens his trunk and out pours all this dust, when the dust settled there she was, a disintigrated steel belted radial that was still smoking all coiled up and hissing at us, unfreeking believable, now that i am older i realize just how lucky i am to be alive in so many incidences, If that steel belt would have made it through and into the car we would have paid dearly,,,,,,, Bob is the same guy that towed me and my brother with the duece and a quarta, we were in a mercury couger, Bob reached the speed of 102 mph with us in tow (by chain)
my bro did not have power brakes because the couger was inop. yet he burnt them out trying to slow Bob down, that was an incident that when the vehicles stopped i almost took a swing at my dear friend, is it any wonder i moved 1,500 miles away! only to meet up with more freeks....

Dr. Rob
09-26-2006, 02:28 AM
AK summed up my thoughts exactly; I just didn't bother to explain. Using a one-way needle roller is maybe not the best solution, but by far one of the simplest-- it just provides a built-in power vs spin evener-outerer.

-----------------------------------------

And since it's up there anyway, ditto on the Dino. Additional info from vague memory... The first Dino models (Enzo F's son Alfredino, + mid '70's. Car accident or sickness*, don't remember) were the FIAT 206's, replaced around 1971 by the 246 model (2.4 liter, 6 cylinder). Around 1972 FIAT gained a majority shareholding of Ferrrari, and sold the cars as such (iirc, there were actually no cars originally sold with the Ferrari badge). 1973-74 sometime the spyder (targa really) version was released. Series ended 1974, replaced by Dino 308 GT4 for a year or two, replaced in 1977 by 308 GTB / GTS, Magnum PI's ride.

*Leukemia? Hemophilia?

topct
09-26-2006, 10:11 AM
Ah, yes I see it now. Thanks guys. And it might not be a bad idea. But I do plan on having a reverse so I think it might be a complication. The vacant lot next to me is to big to be running back a forth to unstick a car.

I have one differential on order and another in the works however. So I will go that route on these first attempts.

Actually my main concern is the steering. The cars I want to build are going to be bigger than a 1/4 scale car and they are going to run in the dirt. There is a large servo made that would work just fine, unfortunatly they cost a few hundred each. And one of the exersizes is to try and build my own high power servo.

Another thing I'm also trying to do is to keep the cost way down. And be able to use parts and pieces that are easy to find and cheap. 1/4 scale cars and parts are hard to find and too pricey. These cars are not only going to be bigger, but a whole lot cheaper. For example, just one tire for a 1/4 scale car can cost $40. The Harbor Freight wheels and tires I'm using cost $10 for the wheel and the tire. And they come on sale for $6.

motomoron
09-27-2006, 11:12 AM
For a 1/4 scale buggy, I see that Northern Tool unit as being WAY to big and heavy.

I'd be making a ball diff from a spur gear from Stock Drive Products. hell, they may have differentials.

See this diagram:

http://www.rctek.com/general/differential_ball_description.html

It's really simple, and every RC car from about 1982 on has had 'em.

topct
09-27-2006, 01:34 PM
The original question had to do with 1/4 scale and yes those diffs are way to big. They do make a small spyder gear type for that size of car and I think I have even seen a limited slip? Very pricey. If I were building that scale I would make a ball type. Or even try the one-way needle bearing idea.

Magic9r
09-27-2006, 02:00 PM
I think you might be able to do something based around the principle of the Salisbury LSD.