lmdesigner42

Efficient 4-speed gearbox

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Hi everyone. This is an efficient 4-speed gearbox design I came up with a while ago using the wave selector and new(ish) 20-tooth clutch gears.

Gearbox1.jpg

It is efficient since only 8 gears and 3 rotating shafts are required, which is near the minimum possible. The shafts in the image are as follows:

  • Yellow - output
  • Red - input
  • Orange - shifter
  • Black - extra, free-spinning

All of the shafts go straight through the gearbox.

Gearbox2.jpg

The compact design is possible by meshing 16-tooth and 20-tooth clutch gears, which gives different ratios at each of the 4 clutch points. Unfortunately, the two shafts with driving rings need to be connected by another gear mesh (in this case 12:24) which results in out of order shifting with the wave selector.

Gear 1 (1st) – 12:16 + 12:24 = 8/3 = 2.67:1

Gear 2 (3rd) – 12:20 = 5/3 = 1.67:1

Gear 3 (2nd) – 16:20 + 12:24 = 5/2 = 2.5:1

Gear 4 (4th) – 16:16 = 1:1

The shifting order issue could be corrected by using a mechanism shifting one driving ring back and forth and then the other, but that would take more space than the wave selector.

The offset of one driving ring by one stud is handled by a sliding 16-tooth gear linking the lower driving ring with another 3 studs higher, putting it in the proper position to mesh with the wave selector. The extra free spinning shaft (black) is used to hold the third driving ring.

Gearbox4.jpg

The transmission fits into a small 9x7x6 box (not including the stepper) which can be easily connected to a chassis represented by the 5x7 frames. The below picture shows how small the core part of the gearbox is.

Gearbox3.jpg

In conclusion, the advantages of this gearbox include small size, few moving parts, and different ratios, while out-of-order shifting is a disadvantage.

Comments and questions are welcome

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A video demonstration+instruction and/or a PDF instruction would be much more appreciated. 

Edited by thekoRngear

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I would appreciate a good habit to presenting gearboxes working under some load. Because there are many, many brilliant ideas and concepts, but part of them are useless if you put some average load on them. They start to skip, lose integrity etc. So I wish to know at start, which one are only nice concepts, and which one actual can deal with some load and be used in RC middle scale models.

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41 minutes ago, keymaker said:

I would appreciate a good habit to presenting gearboxes working under some load. Because there are many, many brilliant ideas and concepts, but part of them are useless if you put some average load on them. They start to skip, lose integrity etc. So I wish to know at start, which one are only nice concepts, and which one actual can deal with some load and be used in RC middle scale models.

I am not disagreeing with you. Since I had troubles working my Land Rover's gearbox right (for me) I started to modify the set and on my way I used a 2 speed gearbox, then a 3+R, and finally a 4 speed one from Dgustaffson (that also extremely similar to the one Sariel made). All these gearbox had caused no big trouble. One particular issue I find is at 3rd gear when you move the vehicle backwards it just don't move (I was not the only one). The remedy was to change the combination of drivetrain's gear and gearbox's gear this way- larger gear (gearbox) + smaller gear (drivetrain/centre diff) caused reduced friction/quiter gearing with reduced dilemma at 3rd gear backwards. If it is changed vice versa the problem intensified. Apart from that I had no problem. But as you have told, I always took the risk of it not working properly with my set. 

A genius gearbox demonstrated above presented with a practical use like Keymaker said is much appreciated.

Edited by thekoRngear

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As you said, the biggest issue with the gearbox is the gears being out of order, but if it were to be shifted by a PU L-motor, like in the Volvo articulated hauler, some programming could be used to allow it to shift through the gears in order. It might look like this: Motor starts in first at 0 degrees, rotates 180 degrees clockwise to second, rotates 90 degrees counterclockwise to third, then rotates 180 degrees clockwise to fourth. (This is just a guess--I haven't built the gearbox, so I am not sure what order the gears are in). The same procedure could be used in reverse for downshifts.

Apart from this suggestion, the gearbox looks promising, with impressive simplicity. The use of an extra driving ring to transfer the shifting is clever. The concerns about durability may or may not be legitimate in this configuration, but I expect that there is a way to brace the ends strongly.

Good work!

Edited by 2GodBDGlory

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12 hours ago, thekoRngear said:

A video demonstration+instruction and/or a PDF instruction would be much more appreciated. 

I don't have much experience with videos, but I'll see what I can do. PDF's are nice, but in this case I think the design is simple enough that they aren't needed.

1 hour ago, 2GodBDGlory said:

As you said, the biggest issue with the gearbox is the gears being out of order, but if it were to be shifted by a PU L-motor, like in the Volvo articulated hauler, some programming could be used to allow it to shift through the gears in order. It might look like this: Motor starts in first at 0 degrees, rotates 180 degrees clockwise to second, rotates 90 degrees counterclockwise to third, then rotates 180 degrees clockwise to fourth. (This is just a guess--I haven't built the gearbox, so I am not sure what order the gears are in). The same procedure could be used in reverse for downshifts.

Apart from this suggestion, the gearbox looks promising, with impressive simplicity. The use of an extra driving ring to transfer the shifting is clever. The concerns about durability may or may not be legitimate in this configuration, but I expect that there is a way to brace the ends strongly.

Good work!

Thanks! I recently got some PU motors, so that may be worth a try depending on what kind of MOC the gearbox goes in.

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As for concerns about strength, I built a copy to test. It could stall a PF L-motor, but not a PF Xl-motor. I modified the original design, as shown here, and now it can stall an XL. The little spacers you can see are cut from the bottom of a 4L ice cream tub, and help keep up tension.

IMG_20200906_145028891.jpg

IMG_20200906_145032763.jpg

IMG_20200906_145036349.jpg

IMG_20200906_145044677.jpg

IMG_20200906_145111715.jpg

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54 minutes ago, 2GodBDGlory said:

It could stall a PF L-motor, but not a PF Xl-motor. I modified the original design, as shown here, and now it can stall an XL.

And this is also very important info (apart from concept of gearbox itself of course). Thanks to that everyone knows, that this concept can be used in RC models without fear to lose integrity or skipping gears. Thank you for that!

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Just now, keymaker said:

And this is also very important info (apart from concept of gearbox itself of course). Thanks to that everyone knows, that this concept can be used in RC models without fear to lose integrity or skipping gears. Thank you for that!

You're welcome!

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Nice work @2GodBDGlory, I'm very impressed it could stall an XL.

I finally got around to adding some bracing and did a practical test of the transmission. It could stall 2x L motors geared down 3:1 in all 4 gears. Also capable of powering a large model with proper gearing.

 

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