Dear all

I'm having some issues with the Lego technic crawler 9398. The 2 front wheels turn in opposite directions. This is the same for the 2 rear wheels, they turn in opposite directions too. (1 clockwise, 1 counterclockwise)

I have read http://www.eurobricks.com/forum/index.php?showtopic=76158. My model is exactly as shown in the picture. Is this correct?

Cheers

Does this happen when the motors are running, or just when you turn one wheel by hand?

How is that possible? The 20t gear drives the differential, not the bevel gears directly, so that doesn't make sense. Did you try just testing it on level ground? I'd like to see some pics of that though.

Does this happen when the motors are running, or just when you turn one wheel by hand?

This happens when i turn it by hand. I dismantled the wheels, and i realise the gear set actually makes the wheels turn in opposite direction. Am i right on this? Which means, my set was functioning properly?

How is that possible? The 20t gear drives the differential, not the bevel gears directly, so that doesn't make sense. Did you try just testing it on level ground? I'd like to see some pics of that though.

Hi Sir

I dismantled the wheels =/

Oh wait, yeah dhc6twinotter is probably right.

It's just what it's supposed to do, so it can turn without stressing the pieces.

Sorry dhc6twinotter, you're still right.

Sorry for all the editing confusion.

Edited July 23, 201311 yr by TwentyLeggedHen

Yes when you hold the model and spin the wheels with your hand the diffs cause the wheels to spin in opposite directions. This however wont happen when the motor is running or something is really weird.

Edited July 23, 201311 yr by EyesOnly

This happens when i turn it by hand. I dismantled the wheels, and i realise the gear set actually makes the wheels turn in opposite direction. Am i right on this? Which means, my set was functioning properly?

Yup, that is correct. The motor makes it harder for the differential to turn, so when you turn one wheel by hand, the other will turn in the opposite direction. When the motor turns the differential, both wheels will turn in the same direction. It sounds like you've built it correctly. Differentials are sooo cool!

So now I have to fix something which was unbroken in the 1st place. :excited:

So now I have to fix something which was unbroken in the 1st place. :excited:

Yep - differentials are a bit counter-intuitive but were an important innovation, both in real-world machines and in lego. This article http://www.howstuffworks.com/differential.htm might be a bit long, but explains things well.

Yep - differentials are a bit counter-intuitive but were an important innovation, both in real-world machines and in lego. This article http://www.howstuffw...ifferential.htm might be a bit long, but explains things well.

This YouTube video also does a great job of explaining how a differential works. It is in B&W, and might appear old, but the principles still apply:

Thanks all for the help! The vehicle is moving well, and my dog is terrified of it!

Cheers!