I have a player character that was at first controlled by rb.velocity.transform times a number that represented miles per hour. The speed worked great, but I wasn’t able to do things like jump and run, or fall and move forward. I’ve been trying out rb.AddForce, but I can’t seem to find that sweet spot that I had. The player either goes flying or barely inches along. Does anyone have info on how to convert realworld units into unity units or vice versa? I don’t care what kind of system is used, but I need it to be readable for myself which means I can’t just use random numbers, even if they look good on screen.
Unity’s units are whatever you want them to be and standardize them to be. For example, the mass of your character’s rigidbody could have a value of 10. If you wanted, you could make this value of 10 be equal to 10 kilograms or 10 pounds. If you wanted the units to be in kilograms then just make all your other objects with rigidbodies have masses that are relative to the player’s character. Ex., if you wanted the units to be in kilograms, and a character’s rigidbod had a mass of 10, that would make for an unrealistically light character (unless it was an infant). So, you’d probably want to have a mass of about 75 (rough weight estimate of an average human in Kgs) . Next, you’d want to determine what units you want to use for size/height/distance. Keeping with metric example, you could standardize your objects so that a size/scale of 1 is equal to 1 meter (I think that’s the default/assumed scaling for the character sizes in Unity’s standard assets). After having determined what you want to standardize you’re units on, you can then tweak the amount and type of forces to add, and if you standardized your units to be relative and realistic to our human real world, then your forces will also have real world values. Unity’s provided first person character prefab (in StandardAssets), unfortunately, has a mass of 10, so you’d have to set that to something more like 75, and the tweak RigidbodyFirstPersonController.cs until you got the look and feel you wanted. Or, work backwards and keep the mass of 10 and then factor the masses and forces of everything by 10/75 (that’s 10 divided by 75, which you’d multiply to factor down sizes and forces). But, I think your wanting to factor up, so you’ll have to tweak RigidbodyFirstPersonController.
First, addressing your comment with your script:
As a bypass for large multiplications, it’s probably reasonable to assume that a character moving “under their own strength” would not necessarily need an arbitrary “muscle strength” factor added in. What do I mean by that?
playerRB.AddRelativeForce(Vector3.forward * (runSpeed * 50));
The 50 multiplied by the runspeed provides an implicit counterbalance against the Rigidbody’s mass. If you want the character’s added force for movement to be treated relative to their own mass, you can do one of two things:
Multiply the force by the mass of the Rigidbody
playerRB.AddRelativeForce(Vector3.forward * (runSpeed * playerRB.mass));
Or change the ForceMode to automatically ignore mass (for 3D AddForce functions only)
playerRB.AddRelativeForce(Vector3.forward * runSpeed, ForceMode.Acceleration);
As for the main dilemma, that's a problem involving friction. [Once you have an object in motion, it stays in motion more easily][1], so stronger forces to begin to accelerate will generally result in higher speeds once you're going (as well as because these are sliding collider shapes as opposed to realistic limbs, which move in highly complex ways).
To combat friction with the ground, you can look at using Physic Materials to reduce friction (static and/or dynamic) for the sake of movement, but that means having to carefully moderate your character’s speed for yourself. You wouldn’t have to fight against the physics system trying to provide realistic(-ish) interactions with natural shapes, but you’d instead have to provide your own basis for movement for your character’s now-unnatural(-ish) physical interactions.
Edit: Whoops, forgot to add this. One further detail to note...
When you’re applying forces to physics-driven objects, you should always apply these forces in FixedUpdate() rather than in Update().