Measuring forces in tendons

Hello,

I want to measure the tension in a tendon attached to an otherwise free body. In lieu of a `tendonfrc` sensor, I'm trying to use force sensors at the tendon attachment sites, with dummy bodies containing the sites.

I expect to see the same force reading from both sensors, with opposite signs, but I'm getting 0 output. I've tried a few configurations and cannot manage to read tendon forces at all by this method. I have obviously misunderstood something.


```xml

```

The nesting works as expected in the following example with no tendon:

```xml

```