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Few builders have ever needed a subtractor, I guess, but those who did will probably welcome a new, smaller and streamlined design. I've designed a bunch of subtractors before but they were all al least 3 studs tall. So this one is as flat as it gets.

Free instructions with parts list included: http://sariel.pl/down/flat-subtractor.pdf

And a totally biased video comparing it to a direct drive:

 

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Nice design! I love these little creations that you post! Keep it up.

See "decreasing number of mocs".

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Very cool design!

I have been using the design below but that has a real flatness advantage.

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As always neat design and it's just great we have innovators like you to push the boundaries of simple, effective designs :-)

 

26 minutes ago, Sariel said:

And a totally biased video comparing it to a direct drive

Then I give two totally biased opinions in favor of the direct drive :-P

- As one of the "cons" on the substractor design I would add "less power". You can just use 1 motor for propulsion instead of 2.

- For the "cons" of the direct drive you name "no simple way to connect a piston engine". The statement depends on the definition of "simple". You can connect a diff between the two driveshafts. Of course, if you turn with counter movement of the motors, the fake engine stops, but the same thing happen when you only use the turning motor on the subtractor.

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10 minutes ago, Jundis said:

- As one of the "cons" on the substractor design I would add "less power". You can just use 1 motor for propulsion instead of 2.

Um, no. Nobody's stopping you from coupling 2, 4 or 10 motors together and connecting them to that one drive input. Just because there's only one axle coming in doesn't mean you're limited to using only one motor.

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48 minutes ago, Sariel said:

Um, no. Nobody's stopping you from coupling 2, 4 or 10 motors together and connecting them to that one drive input. Just because there's only one axle coming in doesn't mean you're limited to using only one motor.

Fair enough, but the same goes for direct drive. My point was: for the sum of the motors, some power goes unused on the substractor gearbox, where on the direct one, most time you use full power.

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51 minutes ago, Jundis said:

Fair enough, but the same goes for direct drive. My point was: for the sum of the motors, some power goes unused on the substractor gearbox, where on the direct one, most time you use full power.

That's one way to look at it, here's another: with direct drive, if you use two motors for drive, each track is only driven by a single motor. You will never get more power on this one track than this single motor provides. With a subtractor, if you couple two motors and use them for driving, each track is powered by two motors simultaneously. This may be an advantage when negotiating obstacles and e.g. one track slips or goes up in the air.

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This is amazing as always Sariel! But sadly I do not have those studded liftarm pieces. Amazing function and I love the flat subtractor!

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One thing I have never seen discussed with subtractors is power loss due to the driving motors backdriving the steering motor. I had this problem a while back with a MOC that lost a lot of power driving straight because of this. How do you prevent this?

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12 hours ago, Saberwing40k said:

One thing I have never seen discussed with subtractors is power loss due to the driving motors backdriving the steering motor. I had this problem a while back with a MOC that lost a lot of power driving straight because of this. How do you prevent this?

Add extra gear reduction between the steering motor and the subtractor. Use a worm gear if there's no other option, that will solve it.

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I used these layouts years ago to retain the power of one motor per track. Too bad I had no idea about the friction issues with worm gears :wall:

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