In the previous article, I assigned IDs to each motor and determined where each motor should be installed.
https://dev.to/takeofuture/trying-vla-part-1-preparing-lerobot-and-assigning-ids-to-the-motors-538g
Now it is finally time to start assembling the robot.
👉 All the parts required for assembly should already be included, so the only tool you really need is a screwdriver.
However, I strongly recommend using a magnetic screwdriver that can hold the screws in place against gravity.
Without one, installing some of the screws can be surprisingly difficult!
For the assembly process, I mainly referred to the following official documentation and videos.
https://huggingface.co/docs/lerobot/main/assemble_so101
https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/lerobot/Joint1_v2.mp4
One thing that may not be very obvious from the video is that I strongly recommend connecting the cable to the next motor before assembling the frame.
Once the motor is installed inside those small frame parts, connecting the cable becomes much more difficult. Looking at the structure, it makes sense — there is simply not much space left to work with afterward 💦.
In this article, I will not cover the entire assembly process. Instead, I will focus on Joint 1 and explain how I assembled it, including several places where I personally got stuck or had to redo the work.
First, each motor comes with a motor horn and screws like these.
An M3 screw has a diameter of 3 mm and, in this case, a length of 6 mm.
An M2 screw has a diameter of 2 mm — measured around the shaft directly below the screw head — and in this case also has a length of 6 mm. The M2 screws used here have a countersunk-style head.
Understanding screw specifications is actually quite useful when building robots like this.
It becomes especially important when planning a project or sourcing replacement parts. At the very least, it is worth asking your LLM assistant about screw standards and making sure you understand them before starting.
This kind of basic mechanical knowledge will become useful again if you build other robots, drones, or similar hardware projects in the future.
If possible, I also recommend learning some basic soldering and how to repair power cables. If you accidentally pull a wire too hard and disconnect or damage it, knowing how to solder can allow you to repair at least some of those problems yourself.
Installing the Motor Horn — Pay Attention to the Orientation!!!
Now let's install the motor horn.
There is one important thing to be careful about at this stage.
When I first installed the horn, I pushed it onto the motor and secured it with an M3x6mm screw like this.
However, the orientation of the horn must match the screw positions of the frame part. Otherwise, you may have to remove it and reinstall it later.
At first, I followed the orientation shown in the video, where the screw holes looked like a diamond shape.
However, I eventually had to redo it because the screw positions on my frame part did not match that orientation.
Push the horn slightly onto the motor shaft, and then secure it using the M3 screw.
The important point is the orientation.
When looking at the four outer screw holes, I initially positioned them so that connecting the holes would form a diamond shape, similar to what appeared in the video.
For my frame, however, the holes needed to form a square instead.
This was my first mistake.
Install the horn at an angle where the four screw holes look like the red circles shown below — forming a square rather than a diamond.
More precisely, you should check the screw positions on your actual frame part at this stage and align the horn orientation accordingly.
The horn on the opposite side does not need to be secured with a screw.
You also do not necessarily need to install it at this stage. It may be easier to place it later while assembling the frame parts so that you can align the orientation correctly.
I will explain this part later, so you do not need to install it yet.
However, just like the other side, its orientation also needs to match the frame. In my case, it needed to be positioned as a square rather than a diamond.
I believe this depends on the frame parts you ordered or printed with a 3D printer.
The screw-hole positions may differ slightly depending on the specific parts you have.
Therefore, before tightening everything, check the screw-hole layout of your own frame and adjust the motor horn orientation accordingly.
Installing the Motor
TIP 1: First, test-fit the parts before tightening any screws.
TIP 2: Connect Motor 1 and Motor 2 before installing Motor 1 into the frame.
I personally struggled because I did not follow TIP 2.
Before installing the first motor into the frame, I strongly recommend connecting the first motor to the second motor.
At this stage, before installing any screws, check that the motor can be pushed properly into the frame part, as shown in the assembly video.
I think it is safer to verify the fit first and only then install the screws.
Do not force the parts too hard.
If you apply too much pressure, you may damage the threaded parts of the frame, strip the screw head, or make the screw difficult or impossible to remove later.
Before installing screws into the motor, first check whether the following frame part fits properly.
The official video installs the screws first, but based on my experience, I recommend checking the fit of the frame part beforehand.
Without tightening the screws, first check that the frame part fits correctly.
Then check whether the motor screw holes align with the screw positions of the frame.
The following image shows one of my mistakes, where the screw-hole orientation was offset by about 45 degrees.
This happened because I followed the orientation shown in the video without first checking the actual frame part.
So before tightening the horn, look carefully at your frame and determine how the screw holes need to be aligned.
I followed the screw-hole orientation in the video and ended up with the wrong position.
So I corrected the orientation.
Again, this may vary depending on the frame parts you are using!
Once you confirm that everything fits correctly, you can tighten the screws.
To be honest, considering that this robot is mainly intended for education and experimentation, if the frame itself holds the motor firmly enough, it may not always be necessary to tighten every screw extremely firmly.
Because of the quality of some screws and 3D-printed frame parts, applying too much force can potentially strip the screw head or damage the threaded hole.
If that happens, removing the screw later can become very difficult.
So first confirm that everything fits properly, and only then secure it with screws.
If you discover, as I did, that the screw holes do not align correctly, one option is to redo the motor horn orientation.
Another possibility, depending on how securely the motor is already held by the frame, may be to leave one side without screws rather than forcing a badly aligned screw into place.
Next, after securing the motor with the M3x6mm screws, install the next frame part.
This is the part with a small protruding section on the upper-right side.
There is another part with a very similar shape, so be careful not to confuse them.
As mentioned earlier, I recommend connecting the cable to the next motor before installing the motor into the frame.
In my case, I assembled the frame first without connecting the cable.
As a result, I had to do the wiring afterward in a very narrow space, which made the work slightly more difficult.
If I had connected the cable beforehand, the assembly would have been much easier.
Rather than simply following the assembly video step by step, I recommend checking the following three points first. Doing this can significantly reduce the amount of rework.
- Check the orientation of the motor horn screw holes against the screw positions on the actual frame parts.
- Push the motor into the frame and test-fit the next part before tightening the screws.
- Before installing Motor 1 into the frame, connect the power/data cable between Motor 1 and Motor 2.
That's it!
In the next article, I’ll finish assembling the robot arm, secure it to the desk, and complete the calibration.
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