My take on 42065

[Saberwing40k]

Well, ErikLeppen posted his work in progress topic for an improved version of 42064, so that spurred me to post this. Like he said, complaining is too easy, so rather than continue to do that, I made an improved version of 42065, to actually make it a Technic set. Going by what I know about the pricing, the set should retail for about $85 dollars. Going by Lego's pricing scheme of having the set cost as much as a regular set with the same part count, and then adding the price of the PF parts, I have about 400 parts to work with, which I did manage to do. And, in rebuilding, I made this into a set that would still be fun, but worth buying for a Technic fan. Now, this model does not keep much of the look, because of how radically different the drivetrain is. But the idea is there.

Ultimate 42065 by Saberwing007, on Flickr

 

The features of this thing include a subtractor, driven by an L motor, and steered by an M motor. This is a modification of @Sariel's longitudinal subtractor mechanism, and works quite well. The other feature is suspension, based on the 2L rubber damper piece. These are used more or less as really stiff rubber bands, and hold up well with a light model like this.

Instructions for the model will be available soon, when Rebrickable approves them. As a note, the magenta pin with stud and the extension cable are not part of the build, and are only to substitute for the L motor's missing cable end.

Edited February 3, 2017 by Saberwing40k
This is more of my take on what 42065 could have been, and not an ultimate model as such.

[Lasse D]

How well does this subtractor work in practice? I recently made a video showing an L-motor driving the subtractor had trouble turning in "rough terrain" (see the 42065 mod topic), but I was using three 8 tooth gears on one side and two 16 teeth gears on the other. This combination has a lot of mechanical power loss. Your design seems significantly lighter, so it might work better.

[Cumulonimbus]

I like your work to incorporate a subtractor mechanism. These mechanisms fascinate me and admittedly I don't fully understand how they work yet. Is there a mechanical advantage in this model? Is it for example faster, stronger or more responsive that the direct drive of the original? The suspension is a nice addition as well, I'm curious how well it will work in real life.

One point for improvement though: for me personally, an ultimate version should also look the part. I rather like the look of the standard 42065 and so far, your version isn't as striking (yet).

Keep up the good work.

[Saberwing40k]

5 hours ago, Lasse D said:

How well does this subtractor work in practice? I recently made a video showing an L-motor driving the subtractor had trouble turning in "rough terrain" (see the 42065 mod topic), but I was using three 8 tooth gears on one side and two 16 teeth gears on the other. This combination has a lot of mechanical power loss. Your design seems significantly lighter, so it might work better.

The subtractor works quite well, and very different from the way your version works. With your version, you're using the tracks as part of the subtractor, and the differentials are mounted in an odd way to. In this version, the subtractor is hard mounted, and braced on all sides. But, I have had some problems with driving over obstacles to, which I blame on using the wrong kind of receiver.

5 hours ago, Cumulonimbus said:

I like your work to incorporate a subtractor mechanism. These mechanisms fascinate me and admittedly I don't fully understand how they work yet. Is there a mechanical advantage in this model? Is it for example faster, stronger or more responsive that the direct drive of the original? The suspension is a nice addition as well, I'm curious how well it will work in real life.

One point for improvement though: for me personally, an ultimate version should also look the part. I rather like the look of the standard 42065 and so far, your version isn't as striking (yet).

Keep up the good work.

The suspension almost does nothing, given that it is relatively stiff, and the model is light. Also, I did some reflection, and decided that this model is not an Ultimate version, but rather how I think that the set should have been out of the box, and I changed the thread title to reflect that. Bodywork is not really my forte, and this was meant to be a quick project, so I'm probably not going to make any changes to the bodywork. I've already moved on to something more interesting.

As for the subtractor, here's something to explain it:

42065subtractor by Saberwing007, on Flickr

A differential, at its core, is a mechanism to divide torque. And, like it can divide a single input into 2 outputs in the axle of a car, it can average 2 inputs into a single output. So, each track has a differential, and each differential has two inputs. In the diagram above, the blue gears are drive, and the yellow gears are for steering. When the steering motor is engaged, the drive sprockets turn in opposite directions. Therefore, the vehicle turns on the spot. When the drive motor is engaged, the drive sprockets turn in the same direction, moving the vehicle forwards or backwards. When both motors are engaged at the same time, then what? Then, each differential splits the difference. The differential for one track, depending on its direction of rotation, will either add the two inputs together, if they are bot rotating in the same direction, or subtract one from the other, if the two inputs are rotating in opposite directions. It's really difficult to explain in words, and I did not fully understand how they worked until I built one, and I urge you to do the same. That's what I love about mechanisms like this. You don't understand them until you see it operating in front of you.

[Lasse D]

Thanks for the added details. That is a neat way to incorporate a subtractor mechanism, and we completely agree that adding some actual "technic" to this technic set would have been a nice addition. I'm looking forward to see what you next project mounts out to be.