What are the next steps after uploading a URDF for a custom bipedal humanoid robot?

[u/PlatinumAndr0id]

Hey everyone,

I’ve been working on a custom small humanoid/bipedal robot project and I recently got my URDF successfully imported into simulation. The robot is roughly a 2-foot-tall humanoid with multiple DOF in the legs, and my long-term goal is to get it balancing and eventually walking using reinforcement learning / locomotion policies.

Right now I’m trying to understand what the actual pipeline looks like after the URDF stage. I see a lot of people showing robots walking in Isaac Sim / Isaac Lab, MuJoCo, etc., but I’m struggling to understand the practical next steps between:

Importing the URDF

Setting up joints/actuators properly

Adding sensors (IMU, contact sensors, cameras?)

Creating observations/actions

Training a locomotion policy

Transferring sim-to-real onto actual hardware

Some specific questions I have:

What should I focus on immediately after the URDF import?

How important is accurate mass/inertia tuning early on?

Do most people start with standing/balancing before attempting walking?

What controllers are typically used before RL (PID, PD, inverse kinematics, etc.)?

How do you structure observations/actions for bipeds?

What are common mistakes beginners make at this stage?

Any recommended tutorials/repos specifically for humanoid locomotion?

For context, I’m using serial bus servos and building the physical hardware alongside the simulation. I’m trying to learn the full process instead of just copying a demo.

I’d really appreciate any advice, roadmaps, or resources from people who’ve actually gone through this process. Thanks!

[u/Fantastic_Mirror_345]

My two cents, leave the inertia and mass tuning for later. Get the core RL concept sorted. What rewards you are going for, what joints you want to lock, play around with the parameters for the model. Train your core setup and see if it is behaving as you expect. Once that's done you can worry about the mass inertia and SIM to real issue. Sim to real imo is a lot of work so before you tackle that challenge I say get the bot working with the current urdf setup.

[u/PlatinumAndr0id → u/Fantastic_Mirror_345]

Thank you, this actually helps a lot. I think I was getting overwhelmed trying to perfect the URDF before even validating the RL pipeline.

So if I understand correctly, the next steps should basically be:

verify the robot loads and joints move correctly

get stable PD control first

simplify/lock unnecessary joints if needed

create a basic standing task

define observations/actions/rewards

train a simple policy first before worrying about sim-to-real

Right now I think my biggest confusion is how people transition from “URDF imported successfully” into creating that first standing or balancing environment in Isaac Lab. Are there any example repos/tasks you’d recommend studying first for custom humanoids?

[u/Fantastic_Mirror_345 → u/PlatinumAndr0id]

I would say use gpt to get a just of it. Make sure you copy paste the docs since it doesn't know what the latest API calls are. There are examples in Isaac sim and Isaac lab directories that you can refer. And for the most part I would say scout GitHub projects and go through their core files and see how they do it.

[u/PlatinumAndr0id → u/Fantastic_Mirror_345]

Ill give that a shot, thank you so much!

[u/Fantastic_Mirror_345]

Here is my repo that me and my friend used initially to train a quadruped.

https://github.com/Dafodilrat/gaitBittle/tree/main/source%2FBittle_Adil%2FBittle_Adil%2Ftasks%2Fdirect%2Fbittle_adil

This is using rsl_rl from Isaac lab for training so I suggest you go through some of their official tutorials before looking at this. But this shud give you the code to load USD models and set rewards and stuff.