Subtractor Issues

[Buddy010702]

So lately, I've been building a tank with a subtractor, but when it tries to drive over anything, it just stops... I'm using one XL for normal drive, and a L motor for steering. There is no gearing for the XL, but I wouldn't think that would cause it... It doesn't even skip gears, it just stalls the motor completely. Is it as simple as gearing it, because I would like a decently fast tank... I don't have too much space either, I just can't find a way for it to work... 

Here's a picture:

Plus, is it possible to have a 2 speed subtractor? (preferably with only one driving ring needed to change gears?)

[DrJB]

You need to flip one of the differentials.

[Dazenie]

In Sariel's Buiders guide the differentials aren't filpped but to be honest I don't really know.

[doug72]

5 hours ago, Buddy010702 said:

Plus, is it possible to have a 2 speed subtractor? (preferably with only one driving ring needed to change gears?)

Yes it is possible with only one driving ring - see this post:

I have built one into my 80hp Fowler Gyrotiller which has a fast 1:1 ratio and slow 3:1 gear ratio's.

My moc now upgraded to a Mk 2 version with improved subtractor.
I will post a picture of the underside later.

Edited January 5, 2017 by Doug72

[doug72]

5 hours ago, DrJB said:

You need to flip one of the differentials.

See this post which shows differentials in opposing positions when using 28Z differentials.
Unit is a flat version of that shown in Sariels guide book.

Images showing subtractor unit fitted to my Mk 2 Fowler 80hp Gyrotiller.
Gives excellent slow speed turns and turns on the spot at both fast & slow speeds.

Underside showing subtractor unit which uses 16/24T differentials.
IMG_4232 by Doug Ridgway, on Flickr

Gear change over lever for 2- speed unit for the L motor.
IMG_4233 by Doug Ridgway, on Flickr

 

Edited January 5, 2017 by Doug72
spelling./ added content

[Buddy010702]

11 hours ago, DrJB said:

You need to flip one of the differentials.

 

7 hours ago, Dazenie said:

In Sariel's Buiders guide the differentials aren't filpped but to be honest I don't really know.

I have sariel's book, and I'm trying to build the studfull one, without studs and with new diffs. I don't need to flip the differentials because the line of gears at the bottom are odd, I don't know how to describe it better, but it works, trust me. Just for some reason have a issue with driving over small obstacles, the motor just stalls. I can't tell if it's just the motor or gearing... I only have the new differentials available, with one XL, one L and one M motors available...

 

Another Issue I have is space... I have plenty of width (about 15 studs between edges of tracks) not too much length, and a varying amount of height... All I can say is it's not a conventional tank. So I'm probably not able to fit the different speeds

5 hours ago, Doug72 said:

See this post which shows differentials in opposing positions when using 28Z differentials.
Unit is a flat version of that shown in Sariels guide book.

 

This looks like It might work, I will get to building with this new design.

 

Thanks!

[suffocation]

I built this test undercarriage a while back and it seemed to work:

 

 

The most obvious downside is that all those half bevel gears are going to have trouble handling high torque. My lack of building skills and having the two inputs coming from what was meant to be the superstructure did limit my options somewhat.

Edited January 5, 2017 by suffocation

[DrJB]

Let's go back to the very beginning:

 

1. What happens when you engage the drive? ANything moves, you hear some parts 'fighting' against each other ... ?

2. If it is easy, I would disconnect one part (gear) at a time, and see if there is motion. That will tell you which gears are working 'against' each other.

3. Do you have an LXF or better yet, some schematics of the drive-train only (motors+gears+axles) with all supporting structure removed? This is the easiest way to 'diagnose' likely issues.

[Buddy010702]

1. No parts were 'fighting' (found out it was just gearing, so motor stalled)

 

2. & 3. Rebuilding a different version, so this isn't possible, but it does seem to work better everytime I rebuild it. 

 

I think my issue was inexperience, the more and more I build the more and more it works. But it seems to be working now, thanks for all the suggestions