What is the cost of Dash, Disengage, and Dodge for a mounted Ranger's Companion?

Question

I'm trying to parse out mounted combat as a ranger with a ranger's companion.

From Controlling a Mount (PHB pg. 198):

You can control a mount only if it has been trained to accept a rider. ... It moves as you direct it and it only has three action options: Dash, Disengage, and Dodge

From Ranger's Companion (PHB pg. 93):

The beast obeys your commands as best as it can. On your turn, you can verbally command the beast where to move (no action required by you). You can use your action to verbally command it to take the Attack, Dash, Disengage, Dodge, or Help action.

Assuming a ranger's companion has been trained to accept a rider, what's the action cost to the ranger of commanding it to Dash, Disengage, or Dodge? I assume it would be free while mounted and cost one action when not mounted.

Answer 1

Your assumption is correct. There is no reason why being a Ranger's Animal Companion would cause a mount to forget or ignore its training. The quote you've included contains the key piece of information here:

You can control a mount only if it has been trained to accept a rider.

So Dash, Disengage, and Dodge are things it has been trained to do when a rider on its back gives the appropriate signals. (Digging in their heels, shaking the reins, however it works.) It doesn't cost any actions from the rider because the mount has been trained to respond to the rider in these ways.

And as you've said, it would still cost one action while not mounted; at that point, you're back to your ability to verbally command it using your action.