What is "clod stall"?

[XPLORx4]

OK, so I've read a couple of threads mentioning a phenomena referred to as "clod stall". I used the search function for this term, and got a gagillion hits on threads that mention it, but never really describe what it actually is.

So, I know what a clod is, and that "stall" has something to do with the motor-on-axle design, but I'm not clear on what it actually is.

[crazy_kanaka]

Clod stall refers to the stalling of one motor. On a clod or berg the two motors are usually hooked up to one esc. When you bind an axle the motor stalls and all the power goes to the motor running the axle that is free. The best and I think still the only way to overcome this problem is to have an esc for each axle.

[XPLORx4]

Thanks for the reply. Interesting... so does the free motor get twice the voltage? It sounds sort of like having an open center diff- the axle with the least amount of traction gets all the power.

[crazy_kanaka]

Originally Posted by XPLORx4

Thanks for the reply. Interesting... so does the free motor get twice the voltage? It sounds sort of like having an open center diff- the axle with the least amount of traction gets all the power.

You should be wiring them in parallel, so no the voltage don't change. And yes it's like an open diff. That's why when they build bergs or clods you add switches to act as dig units for both the front and rear axles. Drivers who experience a bound up axle will usually disconnect the free axle via the switch, and force power to the bound up axle. The rest of the time the stall acts as a diff, and in many cases can prevent breakage while bound up.

[Grizzly4x4]

When climbing a steep incline or ledge with a MOA truck, the weight transfer will put more load on the rear motor than the front. At very low throttle input this extra load can cause the rear motor to stop turning while the front still spins (because the front has less load on it but both motors get the same voltage). That is what is referred to as "Clod stall"; when one motor stops turning and the other does not.
It can happen in other situations too but that one is easy to visualize I think.

Clod stall works as a center diff to keep from binding up and breaking parts, it also acts as a natural dig to keep the rear tires from driving under and flipping the rig backwards.
In the old days we tried to control it with mismatched pinions (something I still do) or really low gearing. With the servo actuated dig switches and dual ESC's that are common today it's much easier to work with and control Clod stall.