[HELP] Small Scale Motorized Bus

[RTL7]

Hello everyone. This is my very first motorized lego vehicle. I'm wondering if somebody could help me to improve all the mechanisms. The vehicle has front steering (this technique requires less space between wheels and mudguards). It's powered by two motors (PF L and PF Servo). I would like to know if there is a way to implement a differential gear. I'm also looking for the best steering technique. I would appreciate any ideas.

 

 

 

 

Edited June 9, 2017 by RTL7

[mocbuild101]

Well if you are looking for compact steering, you should check this out: https://rebrickable.com/mocs/MOC-7176/mocbuild101/small-virtual-pivot-steering/

[RTL7]

8 minutes ago, mocbuild101 said:

Well if you are looking for compact steering, you should check this out: https://rebrickable.com/mocs/MOC-7176/mocbuild101/small-virtual-pivot-steering/

It seems to have very limited angle. But I will find some time to test it out.

[BusterHaus]

4L wide compact differential:

You need a rubber belt to join the two pulleys.  A regular rubber belt will not do the job here, it's too wide and will rub against the 5L half-beam.  I think the old square-cross-section belt should be ok:

Bricklink: https://www.bricklink.com/v2/catalog/catalogitem.page?P=x137#T=P&C=11

If you don't like the pulley solution you can put a couple of gears on the right-hand side of the red #2 connector.  I tried to keep the length as short as possible.

 

[RTL7]

13 hours ago, BusterHaus said:

4L wide compact differential:

You need a rubber belt to join the two pulleys.  A regular rubber belt will not do the job here, it's too wide and will rub against the 5L half-beam.  I think the old square-cross-section belt should be ok:

 

Bricklink: https://www.bricklink.com/v2/catalog/catalogitem.page?P=x137#T=P&C=11

If you don't like the pulley solution you can put a couple of gears on the right-hand side of the red #2 connector.  I tried to keep the length as short as possible.

 

This is a nice one. I think some gears would be more efficient than a rubber belt. The solution is quite good for some bigger vehicles. It should fit my 8-studs-wide bus as well, but here a disadvantage appears - the height of differential gear is the same as my wheels (30.4x14). That would cause the gear almost hitting the floor.

Edited June 10, 2017 by RTL7

[Appie]

Great idea BusterHaus, but I happen to have a few of those old rubber belts and they do tend to touch liftarms next to it as well. One minor note for the diff with this solution: with these tyres, the diff will be very close (1-2mm) to the ground at the 28T side. It should work, but something to keep in mind if ground clearance is a concern.

edit: since the OP said it as well about the diff height, what you could do, is place the diff above the wheels and link them with gears to the wheels, but that would sacrifice some interior.

Edited June 9, 2017 by Appie

[BusterHaus]

@Appie Too bad they won't fit - thanks for checking, I don't have access to them at the moment.  I guess the solution is to have it gear driven.

Edited June 9, 2017 by BusterHaus

[TinkerBrick]

@BusterHaus nice idea. However I do not understand why it has to be driven by a belt ? Would an axle through the red connector, the pulley and the gear work as well?

[BusterHaus]

@TinkerBrick The motors are side by side in his build, so the output from the drive motor is offset.  The pulley design is actually not great, as the 3L axle is offset from the center of the motor by half a stud.  I put it together quickly at lunch, I noticed the error just now.   It will have to be driven by gears on the right side of the red connector, and the motor shaft cannot pass through piece #15100. 

[mocbuild101]

15 hours ago, RTL7 said:

It seems to have very limited angle.

That is because of it's design.

 

14 hours ago, BusterHaus said:

4L wide compact differential:

That is a very small differential housing!