StudWorks

Differential Causing Gear Ratio Increasement? + Drivetrain Clicking

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Hi. I was working on my car MOC (with a four-speed gearbox designed by Sariel) and had some unfortunate events happen.

As stated in the title, the differential is somehow making the gear ratio higher than I need it. The gear moving the diff is moving at the same speed as the power input, but the wheel hub moves one rotation for every 3/4 rotation that I move the input shaft.

Is this differential piece supposed to do this? I want the wheels to move at the same speed as the motor at 4th gear, which brings me to my next problem.

I hear rapid-fire clicking noises every time my car is in 3rd and 4th gear. This happened to my other MOCs too, but I was able to solve it.

Since the car is to be powered by two EV3 large motors, I actually believe there might be a clutch mechanism in the motors such as in the Technic linear actuators that also make a terrible clicking sound when they move all the way up or down.

Whatever it is, I'm open to responses and hope the Eurobricks community could provide an explanation and solution about both of these issues.

Here's some pictures, the orange and red pieces in the first pic were for testing the rotations.

'Kx2c9Hq.jpgoF6RNyP.jpg

Thank you for your time. :classic:

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The ratio issue is due to the ratio between the gear driving the diff (20t) and the diff itself (28t).

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7 minutes ago, Didumos69 said:

The ratio issue is due to the ratio between the gear driving the diff (20t) and the diff itself (28t).

That's what I thought, it is a small gear moving a big gear, so it should be a gear reduction. I don't get why it is the opposite.

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6 minutes ago, StudWorks said:

That's what I thought, it is a small gear moving a big gear, so it should be a gear reduction. I don't get why it is the opposite.

Are you blocking one of the outputs of the diff? In that case the other output will move twice as fast as the diff.

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3 minutes ago, Didumos69 said:

Are you blocking one of the outputs of the diff? In that case the other output will move twice as fast as the diff.

A matter of fact, that seems to be the case. For some reason when I rotate the input shaft one wheel hub always moves faster than the other.

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55 minutes ago, StudWorks said:

A matter of fact, that seems to be the case. For some reason when I rotate the input shaft one wheel hub always moves faster than the other.

Because another one have a higher (slight but still enough) friction. So, you really can block one wheel and then just divide all results by 2.

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3 minutes ago, Void_S said:

Because another one have a higher (slight but still enough) friction. So, you really can block one wheel and then just divide all results by 2.

I think you're right. Anything I could do about the clicking? I drive in 3rd and 4th and it makes these clicking noises that are as loud as anti-lag.

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1 minute ago, StudWorks said:

I think you're right. Anything I could do about the clicking? I drive in 3rd and 4th and it makes these clicking noises that are as loud as anti-lag.

First, I would put any other motor to exclude its "clicking" and then inspect all gears that a engaged in 3-4th while the whole transmission rotates - usually the ones that are clicking and skipping are visually "jumping". Normally, the most possible place is the gear that has the higher torque and the worse secured - it's enough to have 1mm flexibility to jump between teeth.

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1 minute ago, Void_S said:

First, I would put any other motor to exclude its "clicking" and then inspect all gears that a engaged in 3-4th while the whole transmission rotates - usually the ones that are clicking and skipping are visually "jumping". Normally, the most possible place is the gear that has the higher torque and the worse secured - it's enough to have 1mm flexibility to jump between teeth.

That seems interesting. I'll show you a picture of the transmission but I'm a bit busy.

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@Didumos69 and @Void_S I think I finally found out what the clicking noise was.

lYEXjMg.jpg

I put the chassis in drive and pushed it until it generates enough friction to cause a click and I found out where it came from. The CV-joints in the differential that connect to each wheel are getting dislocated and snapped back in again, causing the clicking noises.

You can see the joint popped out in the picture above. Would love some help from a Lego physical therapist. :grin:

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You should prevent the joints from dislocating. Can you add bushes and half bushes to the axle inserted in the CV-joint? They should cover the naked part of the axle completely. However, if the axles need to be able to slide in and out the CV-joints, for instance when you compress / decompress the suspension, then it will be much harder to solve this issue.

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17 minutes ago, Didumos69 said:

I remember @PorkyMonster doing this:

I thought about replacing the CV joint with a universal joint instead of doing this but I'm worried that the u-joint will break.

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2 hours ago, StudWorks said:

I thought about replacing the CV joint with a universal joint instead of doing this but I'm worried that the u-joint will break.

It depends on the torque. The best way to save them is to gear-up the drive train that comes through the CV or Universal joint, but keep in mind that additional gearing up and down causes additional friction.

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8 hours ago, StudWorks said:

@Didumos69 and @Void_S I found the actual issue that caused the clicking. It indeed was gear skipping and I hope to fix it tomorrow.

:thumbup: keep us posted.

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@Didumos69 and @Void_S here's the pictures of the problem.

j3rLfNe.jpg

There is a 4L axle with stop below the big gray gear. That axle has to be there.

oo0yRLl.jpg

The spot where the gray bush is on the gear is where there is no place to reinforce that gear.

B7XBiJr.jpg

The clicking comes from no bracing in the axle with this piece I am pointing at. I can't replace it with any other piece because it would touch the big gear.

I'm thinking of swapping the 4L with stop with a normal 4L and replacing the normal 4L with the gear and bush with a 4L with stop but I'm not certain if the stop being buried into the beam's hole is enough to stop the clicking.

Any advice for fixing this would be appreciated.

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That will be hard without using more space. Can you skip the red connector in which the 4l with endstop is inserted and use a longer axle instead. Then you're axle might be slightly stiffer. You might also try with two knob wheels instead of the 16t gears. They won't slip, but might give more friction.

In general my advice is to always support axles on each side of each gear.

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8 hours ago, pleegwat said:

Could you replace that bush with a 3l beam fixed on both sides?

That will collide with the 24t gear above. The middle section of a bush gives just enough space for the teeth of the 24t gear, but a beam, which is wider than that section, does not.

Edited by Didumos69

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14 hours ago, StudWorks said:

B7XBiJr.jpg

What if You leave the bush piece away, and use this part (below) as bracing in the liftarm, what Your finger resting on? As I see, there is space for it, and would be the easiest way. Of course 3L liftarm + 2 pins can do the job as well.

6055630

Edited by agrof

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28 minutes ago, agrof said:

What if You leave the bush piece away, and use this part (below) as bracing in the liftarm, what Your finger resting on? As I see, there is space for it, and would be the easiest way. Of course 3L liftarm + 2 pins can do the job as well.

Will collide with the 24t gear above. Only a bush-shape will leave enough space for that gear.

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Didn't take the time to look into deeper, correct... @StudWorks Than I have no better idea than changing the gear ratio there (reduce). It is still smaller sacrifice, than complete redesign - in case. Of course the latter is more challenging. :wink:

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5 hours ago, agrof said:

Didn't take the time to look into deeper, correct... @StudWorks Than I have no better idea than changing the gear ratio there (reduce). It is still smaller sacrifice, than complete redesign - in case. Of course the latter is more challenging. :wink:

@agrof and @Didumos69 I had an idea.

This is a mock-up of my gearbox.

2rMM7vC.jpg

Instead of having the gray gears on this side...

Mfvugo2.jpg

I'll put them on the same side as the black gears. It seems to perform exactly the same way as it did before. Any thoughts? :classic:

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52 minutes ago, StudWorks said:

I'll put them on the same side as the black gears. It seems to perform exactly the same way as it did before. Any thoughts? :classic:

Assuming the 8t gear is still on the same axle and the 24t gear too, that should indeed give the same behavior.

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