1:1 Differential

[frankendat]

Ratsun Community: The idea of a 1:1 differential surfaced again in a late Friday night conversation. (In an alternative vehicle concept) I have internet and salvage yard searched for a 1:1, thinking I might find one on an old tractor/ditchwitch or dump truck. I have found the little ones for go karts, but am skeptical they could handle the stress and torque of even a small (2000-2500lbs) vehicle.

Since Ratsuners are from different backgrounds and vocations, thought to cast a net here. I seek low cost-ish options, meaning I could be tempted to part with hard earned for the right unit, but not the funds needed for custom build or land racing units.

 

Any ideas?

[datzenmike]

Land speed record???

 

Gears multiply torque.

 

If your first gear is 3.321 and the differential is 3.545  you can idle along at 4 mph @ 700 rpm. Easy to let the clutch out and slip till at or above 4 mph and away you go. The transmission plus the differential gives you a torque multiplication of almost 12 times!

 

If you run a 1:1 or basically no differential you would have to smoke the clutch slipping it till you reach 16.3 mph. And your torque multiplication is only 3.321 times. Almost the same as taking off in 4th. You would definitely need a push start

 

 

[frankendat]

3 hours ago, datzenmike said:

Land speed record???

 

Gears multiply torque.

 

If your first gear is 3.321 and the differential is 3.545  you can idle along at 4 mph @ 700 rpm. Easy to let the clutch out and slip till at or above 4 mph and away you go. The transmission plus the differential gives you a torque multiplication of almost 12 times!

 

If you run a 1:1 or basically no differential you would have to smoke the clutch slipping it till you reach 16.3 mph. And your torque multiplication is only 3.321 times. Almost the same as taking off in 4th. You would definitely need a push start

 

 

In my internet searching I found manufacturers of 1:1 differentials used in Bonneville Salt Flat cars, primarily for attempting land speed records. However, they are costly.

I posted before of my endeavors with hydraulics. There would be no difficultly with starting torque with a high enough displacing hydraulic motor, however such motors are primarily used in low speed operation. Attempting to strike a balance between low speed hydraulics and higher mph, I have acquired a couple 4.9 c.i. motors. These motors are acceptable, but not if ran through even a low ratio differential. 
The 4.9 will turn 800 rpm continuously and reliably. 800 rpm with 31 inch tires, through a 1:1 transfer case and a  1:1 differential could maintain a 2000-2500 pound  vehicle at 55-65 mph (given a slightly smaller than average aerodynamic profile and discounting a percentage for rolling resistance and gear inefficiencies.) 
However, without a 1:1 differential, it would be necessary to offset the lowest ratio 4x4 differentials that I have been able to acquire (3:07) by using a 3:1 transfer case mounted in reverse (creating a .33:1 ratio). While this would be close enough to 1:1, it would increase gear inefficiencies and introduce problems with noise and gear cooling.
 I really would like to find a 1:1 differential  (or close to it) from some industrial, construction, or marine application, besides the go-kart options and it should exist.  

[datzenmike]

At 800 rpm you would only be making a handfull of HP and not enough to push through the air. Strictly concerning air resistance or drag only, it takes 4 times the hp to double your speed. If you have 1,000 hp and can just get to 200 mph you will meed 4,000 hp to go 400 mph

[frankendat]

On 2/17/2024 at 11:04 PM, datzenmike said:

At 800 rpm you would only be making a handfull of HP and not enough to push through the air. Strictly concerning air resistance or drag only, it takes 4 times the hp to double your speed. If you have 1,000 hp and can just get to 200 mph you will meed 4,000 hp to go 400 mph

True a handfull of HP (30-35) but 225 nm (166 ft lbs) of torque, will that change your answer?

[datzenmike]

A 3.321 first and 3.545 differential will multiply 166 ft lbs* of engine torque to almost 1,954 ft lbs

 

Remove the differential and that drops to 551 ft lbs

 

 

* This is likely maximum engine torque and no one starts off from a start revved up to maximum. It would be like trying to start your truck in 4th or 5th. I suppose you could get a push start but even at 100 mph the engine is no where near it's maximum power  and air resistance is piling up quickly. You may not be able to get past 100mph. A 2 to 1 differential would allow the engine to rev twice as high at 100 MPH make more power and go slightly higher.

 

 

Air resistance as I mentioned increases with the square of the speed. You will need 4 times the power to only go twice as fast. Find the frontal area so you can roughly figure out how much drag and air resistance you will be facing at that speed.

 

There used to be on line calculators that you plug in the HP at RPM, frontal area, aerodynamics, gearing, tire size, and more and you could see roughly how fast you combination would go.

 

[flyerdan]

Rather than sourcing a rather rare and pricey diff, would it be possible to put another 4 speed trans in backwards, so it would be acting as a secondary overdrive?  When in 4th it would be a straight through 1:1, 3rd would be the reciprocal of whatever ratio it was, same with second (if you could maintain it).  

Given all the ratios from the gears, plus the differential ratio, all these could be plugged into an Excel sheet to get the pattern for each combo so you could find a shift pattern that would keep the torque curve at the optimum, so you don't run out of power.

I can only imagine that the aux tranny would not be happy at being run backwards, and might require an additional pressure type  moly-lube setup to keep it from grenading in protest.  It can't be a unique idea, and has probably been tried before; there might be some documentation of it somewhere, be interesting...

[datzenmike]

With only 166 ft lbs

1 hour ago, frankendat said:

True a handfull of HP (30-35) but 225 nm (166 ft lbs) of torque, will that change your answer?

 

Steam or diesel? HP and Torque at what RPMs???

 

Either way you won't push aside much air with 35 hp. Maybe 70-80 MPH?

[frankendat]

22 hours ago, flyerdan said:

Rather than sourcing a rather rare and pricey diff, would it be possible to put another 4 speed trans in backwards, so it would be acting as a secondary overdrive?  When in 4th it would be a straight through 1:1, 3rd would be the reciprocal of whatever ratio it was, same with second (if you could maintain it).  

Given all the ratios from the gears, plus the differential ratio, all these could be plugged into an Excel sheet to get the pattern for each combo so you could find a shift pattern that would keep the torque curve at the optimum, so you don't run out of power.

I can only imagine that the aux tranny would not be happy at being run backwards, and might require an additional pressure type  moly-lube setup to keep it from grenading in protest.  It can't be a unique idea, and has probably been tried before; there might be some documentation of it somewhere, be interesting...

I pursue that path as well, my thoughts are a divorced transfer case backwards. Either a datsun T100 (2:07:1) or a Sami T-case with 3:1 gears, again mounted backwards. Also considered a 3:1 glimmer type belt drive, or an old Jeep twin stick. The T100 and the Jeep twin stick stand out as best choices because I already own them. I have considered many different options, but it quickly gets complicated and I don't like complicated especially in a potential mountain rig. So, I come back to a low cost 1:1 (or close to it) differential. But, I have looked and posted on many different forums and I may have to face it, that no, non custom or non high dollar (such as a quick change) options exist. 

[frankendat]

22 hours ago, datzenmike said:

With only 166 ft lbs

 

Steam or diesel? HP and Torque at what RPMs???

 

Either way you won't push aside much air with 35 hp. Maybe 70-80 MPH?

70-80mph would be awesome! I am cautiously crossing fingers for 55-60 MPH           

[Stoffregen Motorsports]

Be careful running a t-case backwards. It may affect the oiling. Ask me how I know...

 

Have you said yet what engine you're using? ELectric?

 

A 1:1 diff in most cars would be like starting off in 4th gear.

 

[datzenmike]

A 35 hp motorcycle can do that but small and light

[Icehouse]

I'm not sure why you need it but it sounds like a fun project!!!!!!!!!!!!!  It's got me thinking.  I mean Nissan Runs their diffs backwards all the time in the 4WD's.