Transmission question. Will it work?

[Dirty_Vinylpusher]

Hey guys, as some of you know I tinker around with building my own, rather large, RC cars.



I've got this idea for a 6-wheeler with rear 4 wheel drive.



I'm wondering if it would be possible to drive the rear 4 wheels off one diff.
Any thoughts on this?

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[stevehuckss396]

Why wouldn't it work? Looks like it will to me.

 

[johnthomp]

i found years ago with me lego set that it can be done as in the diagram but due to the ratio and rotational patterns of the wheels when the vehicle is turning will put exessive force on the wheels halfshafts and chains breaking nearley all items at one point or another
a better way would be to run a second shaft out of the back of your first diff and put the second diff upside down to work on the opposite hand but makes the wheels run in the right direction
if in doubt build it with technic lego thats what i do even though i get called allsorts for playing with the stuff at my age i gues some things you just never grow out of ;D
hoope this helps fella
regards john

 

[FIXIT]

No problem
As long as the chain drive can take the max power from the diff as at times all the drive will be on one wheel only and a slight amount of scuffing / tyre windup may occur but i see no problem.

The early four wheel "BobCat" loader has one hydraulic motor each side which uses a chain to each wheel and the British army had a light buggy with eight wheels the front two steered and the others with a chain but i don't know if that ever went in to production.

Try It !

 

[johnthomp]

im just wondering are you useing premade off the shelf rc car diffs or are you gonna build your own from scratch if so that would be one very interesting thread as i see some people on here with the genious to build v6 and v8 ic engines
ps if your useing off the shelf diffs i know from experience the teeth in them can strip out quite easily and be very expensive to replace :'(
regards john

 

[fltenwheeler]

Look and any Motor Grader. ;D

Tim

 

[Dirty_Vinylpusher]

im just wondering are you useing premade off the shelf rc car diffs

The diff I have in mind is a 1/5 scale FG diff which I'm told is super strong.

As long as the chain drive can take the max power from the diff

Should do as I'll be using pocketbike chain.

i found years ago with me lego set that it can be done as in the diagram but due to the ratio and rotational patterns of the wheels when the vehicle is turning will put exessive force on the wheels halfshafts and chains breaking nearley all items at one point or another

Yeah but LEGO is a little bit different from 1/4 or 1/5 scale rc components






What I'm really asking, I guess, is this.
Given that all the components are strong enough, is there any difference in rotation between the wheels on the same side of the car?

Will the "front rear left wheel" rotate at the same speed as the "rear rear left wheel" when going through a corner?

Or rather: SHOULD the "front rear left wheel" rotate at the same speed as the "rear rear left wheel" when going through a corner....?

 

[Dirty_Vinylpusher]

And would there be any benefit from having the "Front rear wheels" track narrower than the "Rear rear wheels"?

 

[dsquire]

Dirty_Vinylpusher

For the most part I think that the front and rear wheels on one side will be very close to the same rpm on the same side. The outside wheels will be going slightly faster than the inside wheels on a turn. Naturally on a straight run they should both be the same rpm. That will be the reason for the differential.

I don't think that having a narrower front track would be of any benefit. In fact I think that it would be a hindrance. If it was narrower than it would cause it to have a different turning circle therefore a different rpm versus the rear wheel which would cause one or the other to slip, probably the one with the least traction.

I am assuming that we are talking about a 4 wheeled vehicle here. If we are talking about a 6 wheeled vehicle than the same things would apply. You can rest assured that I will be watching to see what you do with this.

Cheers

Don

 

[Dirty_Vinylpusher]

I am assuming that we are talking about a 4 wheeled vehicle here.

Don, I think you misuderstood my question slightly.

See pic in my first post.
6 wheels, with the rear 4 driving off one diff.







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[dsquire]

Dirty_Vinylpusher

Your right. I had seen that earlier but didn't go back to look at it again when I made the post. As a 6 wheeler I can see no problem with doing it that way. All tracked vehicles are basically done this way, with the track taking the place of the chain and being strung over the wheels instead of the sprockets.

What I said about the narrower track in the earlier post would still apply here but not with as much effect.

I had been wondering to myself how you were going to drive the front wheels with a sprocket and steer them at the same time, but now that we know it is for a 6 wheeler it's OK.

Cheers

Don

 

[FIXIT]

HI- again

yes the two chain driven wheels on ether side will revolve exactly at the same speed because they are mechanically connected (the same as having gears)

in a corner there won't be any significant speed difference as long as they are close to gether IE. like the back of a artic trailer.
any small difference will 'scrub' the tyre with the less grip but not noticeable,

Not knowing what you are using this for, racing ,rough terrain , but be aware that as suggested if you weren't to use a chain and put a diff between the two wheels when one of the wheels looses traction it would increase speed and you will lose power to the other one.

As for a narrow track on the front ,without recalculating the steering geometry you will make the steering
less efficient .

Google 'ACKERMANN steering angle' on Wikie and that will explain why.
hope this helps
Steve

 

[Dirty_Vinylpusher]

As for a narrow track on the front ,without recalculating the steering geometry you will make the steering
less efficient .

No no what I meant when I said that was to make the track width of the front set of rear wheels , or if you like the middle set of wheels, narrower.
Not the front wheels as in the ones that steer.

ACKERMANN

I'm familiar with this and have applied it on one of my other cars already.
It has no diff at all on the rear axle and applying the Ackermann angle made a huge difference.



[ame=http://www.youtube.com/watch?v=JRYwSfxjcWk]http://www.youtube.com/watch?v=JRYwSfxjcWk[/ame]

 

[Brian Rupnow]

What you are proposing will work fine with no problems.---Brian

 

[dsquire]

No no what I meant when I said that was to make the track width of the front set of rear wheels , or if you like the middle set of wheels, narrower.
Not the front wheels as in the ones that steer.

If you do this, then when you make a turn the front rear wheels will have a different turning radius therefore either the front/rear or the rear/rear wheel will slip to a small extent. How much effect this has on performance is hard to predict but I guess a lot would depend on the terrain that you are driving on, sand, pavement, grass etc.

Cheers

Don

 

[johnthomp]

in my original reply i was just implying it would work better with 2 diffs rather than 1 and built the thing in lego a few years ago after watching a documentary programme on the early pre war jeeps and other 4 wheel drive vehicles and how the discovered nd overcome the problem of loseing traction when turning due to the wheel ratio being equal as front to back axle and being locked at that ratio
i made it out of lego because its simple to us quick and no big deal if it breaks but the way lego is it is made in such a way that if something is the wrong way or isnt set true to run perfectly it will snap the click together chain links or seperate two or more gears
going off the principle and my own rule of thumb if in doubt try it with toys such as lego or meccano
i just found that 2 diffs are better than 1 but in this case 1 diff should work fine if built strong enough wich its aparrent the matereals list is more than adequate for the job
i say go for it cheif it seems to have a 99.999% sucsess probability about it
regards john

 

[SAM in LA]

An old trick I learned many years ago is to lightly apply your brakes when the differential sends all of the power to the slipping wheel. This is what we would do when out in our 4x4's and we didn't have locking differentials.

SAM

 

[Maryak]

Don't see why it would not work. A belt rather than a chain may give some leeway for the very slight difference the further the axles are apart.

Best Regards
Bob

 

[John S]

Do a search on Scammell Coffee Pot.

http://freespace.virgin.net/scammell.man/index2.htm

They used the same idea, there was a massive chain inside the rocking beam.

Click on History and Film Clips.

John S.