Didumos69

[WIP] RC Off-roader w/ Dual Diagonal Drive

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Have you thought about reducing the number of 90 degree limiter is the shifter assembly? I was able to keep a pair of similar transmissions synchronized with just 1 90 degree limiter.

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3 hours ago, deehtha said:

Have you thought about reducing the number of 90 degree limiter is the shifter assembly? I was able to keep a pair of similar transmissions synchronized with just 1 90 degree limiter.

Good idea, one would be enough, but the closer to the rotary catches, the better. That's why I have two. I already installed only one silicon band on each limiter, but having just one limiter would be even better.

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With this powerful shifter I hope I will resolve the 4th-to-3rd gear shift issue:

In this type of shifter the return of the servo is very easy, because the servo output only needs to slip along a ratchet. To make even more powerfull quarter turns, I have been looking into a way to also utilize the return of the servo in making a shift. I found a way with two differentials, but it introduced too much slack. However, by adding a spring that is compressed when the servo is centered and expands when the servo turns left or right, I could amplify the torque of the shifter. The servo is powerful enough to compress the spring when it returns. I don't have a video, but it looks like this, and it works excellently. I will be incorporating this concept in the Dual Diagonal build soon.

960x540.jpg

Edited by Didumos69

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Wow, it's like my nephiew. Grown a lot since I've seen him last time. :grin: Loking forward to see it in work. :thumbup:

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Good news on the stepper. After a lot of trial and error I finally got the stepper working through all gears at full speed. I tried the smaller stepper, bit it was too sensitive to small changes. The bigger stepper simply never fails as long as it's operated with enough power. Eventually I ended up with this setup. It's almost the same as the original design. The main difference is that the shifter pushes each shift slightly further than 90 degrees to compensate for the flexibility in the parts between the shifter and the gearbox.

800x450.jpg

However, I ran into another problem. Over the last updates, which did not include any changes to the drive trains, the model started making a very strange sound in 4th gear. It's like something is resonating, but I'm not sure. It's really an aweful sound and it seems to induce friction too. I can't really locate the source. I think it's the gearboxes, but might also be the motors. I checked over and over again, but everything is connected correctly and all axles and gears are running very smoothly. The strange thing is that everything was working okay before.

I made two hasty videos that present the sound. If there is anyone who has experienced this behavior or has a clue as to what might be going on, then please let me know what you think. Any help is much appreciated.

 

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Absolutely stunning work :wub_drool:

As for the weird noise, I wonder if it has to do with the hubs. Maybe the combination of weight, torque and speed is such that once you hit fourth gear the hubs struggle to stay straight/aligned and generate that unbaconliscious squeal.

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Very odd noise.  In the video of the car driving it sounds like something is fluctuating.  The only thing I can think of is if you have multiple U-joints, are they aligned properly?  Or perhaps; some of the gear / drive train in 4th gear is not solid.  That however seems unlikely knowing how you build everything solid.

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Did you check the PF XLs? To me it sound like the motor might be failing.

22 hours ago, Didumos69 said:

the model started making a very strange sound in 4th gear. It's like something is resonating,

Maybe the motor doesn't have enough strength for the 4th gear. What could be happening is that the insides might start shaking a little, the rotor part, and then produce a slight vibrations that are resonating, and it just so happens that they are the same frequency as other connected parts near the motor and that's why vibrations are easily transfer all around.

"In mechanical systems, resonance is a phenomenon that occurs when the frequency at which a force is periodically applied is equal or nearly equal to one of the natural frequencies of the system on which it acts."

That's why real engines have sort of a buffer between the crankshaft and the engine block, otherwise the whole car will shake itself to pieces. This is also the reason why buildings and bridges are falling.

This is the only thing that comes to my mind since everything else is ok.

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22 hours ago, suffocation said:

As for the weird noise, I wonder if it has to do with the hubs. Maybe the combination of weight, torque and speed is such that once you hit fourth gear the hubs struggle to stay straight/aligned and generate that unbaconliscious squeal.

But the effect also hits in without the wheels touching the ground. Also, due to this effect the model actually goes faster in 3rd gear without this effect. If you are are right I would expect the effect also in 3rd gear.

22 hours ago, technic_addict said:

Very odd noise.  In the video of the car driving it sounds like something is fluctuating.  The only thing I can think of is if you have multiple U-joints, are they aligned properly?  Or perhaps; some of the gear / drive train in 4th gear is not solid.  That however seems unlikely knowing how you build everything solid.

I don't use multiple u-joints and the bracing is very solid everywhere. But maybe I made an error while building. If I don't find the issue, I will take it apart and rebuild it. But that would mean about 6 to 8 hours of work.

1 hour ago, pagicence said:

Did you check the PF XLs? To me it sound like the motor might be failing.

Maybe the motor doesn't have enough strength for the 4th gear. What could be happening is that the insides might start shaking a little, the rotor part, and then produce a slight vibrations that are resonating, and it just so happens that they are the same frequency as other connected parts near the motor and that's why vibrations are easily transfer all around.

"In mechanical systems, resonance is a phenomenon that occurs when the frequency at which a force is periodically applied is equal or nearly equal to one of the natural frequencies of the system on which it acts."

That's why real engines have sort of a buffer between the crankshaft and the engine block, otherwise the whole car will shake itself to pieces. This is also the reason why buildings and bridges are falling.

This is the only thing that comes to my mind since everything else is ok.

This makes sense and I'm familiar with resonance and the natural frequency or eigen frequency of structures. This is also why soldiers don't march on bridges. I should be able to check whether the motors have some kind of vibration when the effect hits in.

Thank you all for thinking with me.

Edited by Didumos69

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I think that you should check everything around the Z24 gears, sometimes they touch other parts when these gears are under load. 

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to troubleshoot your motors is simple, just flip it upside down and turn it on and hold a wheel, since there is two drive trains, you'll here the difference on which has a bad motor. if its not the motor then you inspect your gears.. a little chip can cause those issues you hear ...    

Lego technic

 

Edited by sirslayer

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14 hours ago, pagicence said:

Maybe the motor doesn't have enough strength for the 4th gear. What could be happening is that the insides might start shaking a little, the rotor part, and then produce a slight vibrations that are resonating, and it just so happens that they are the same frequency as other connected parts near the motor and that's why vibrations are easily transfer all around.

I checked this morning and I don't feel any vibration in the XL motors, not in any gear. I pressed my nail against the 24 gears on the output of the motors quite hard to disturb any vibration, but the noise was still there. The noise comes from the gearboxes, I'm quite sure about that now, but the resonance could of course still come from the motors.

12 hours ago, anatolich said:

I think that you should check everything around the Z24 gears, sometimes they touch other parts when these gears are under load. 

Thanks! The only 24t gears are directly attached to the motor outputs and they don't rub anything, also not under high torque. At least that's what I can see. The only parts they could collide with are two bushes attached to adjacent axles. The differentials in the gearbox also have a 24t side but these have plenty of space around them.

5 hours ago, sirslayer said:

to troubleshoot your motors is simple, just flip it upside down and turn it on and hold a wheel, since there is two drive trains, you'll here the difference on which has a bad motor. if its not the motor then you inspect your gears.. a little chip can cause those issues you hear ...   

I checked this, but both drive trains produce the same sound. The effect is slightly stronger in the right drive train.

There is one section in the gearbox I suspect most, but I can't reach the gears. I checked all other gears by pushing a nail against them so any resonance in that gear should at least be reduced, without any result. The gears I couldn't check are idle in 4th gear and in 4th gear they spin 9 times the XL motor output speed, which is 3 times the transmission output.

Edited by Didumos69

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What about diving into the sea of sin, and lubricate all the gearings (silicon spray)? If the phenomenon still remains, than it must be indeed rebuild required.

Edited by agrof

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Just one more suggestion, if you are considering a rebuild, how about using brand new pins? Will that have slight or any effect at all?

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On 3/25/2019 at 12:43 PM, pagicence said:

Just one more suggestion, if you are considering a rebuild, how about using brand new pins? Will that have slight or any effect at all?

Thanks for the suggestion! I will keep it in the back of my mind when I get to it.

On 4/26/2019 at 8:23 PM, 1963maniac said:

What happened to this topic? Where did everyone go?

I'm sorry, but I'm having a short break from LEGOs, but I can't imaging not coming back.

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8 hours ago, ozacek said:

What happened with this project, is it off? It was looking very promising..

I decided to park this project for now. I don't regard it as failed, because I learned a lot from it. I will most likely split this project into two, a model with dual diagonal drive and a model with a 4-speed gearbox that can run through all gears at speed. I already have an idea for a 4-speed gearbox with automatic clutch, which disengages the entire gearbox during shifts. Both RC models of course.

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Another zombie post, but maybe I have another angle, as a motorcyclist.

You can shift a motorbike's sequential gearbox up without the clutch, as long as you dip the gas at the same time to allow some slack into the system. Quickshifters do the same, by sensing an input on the gear pedal and cutting the spark for a few cycles until the next gear engaged.

You can also do it on the downshift, and quickshifters can do this. However, it's a much more tricky operation and more often results in grinding gears... You don't tend to try it too many times more after that.

It would be considered very lacking of mechanical sympathy to attempt a gearshift without introducing that little slack in the system. Indeed most times it's not possible as the dogs on the gears are slightly tapered to pull themselves tighter under load.

Can you solve the shifting issue by software? Can the app cut drive to the XL motors for the briefest moment just to introduce some slack, then the shift goes easy?

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