I am trying to write a Lua script for my rover to FOLLOW a flying copter. My copter SYSID = 12, and I set rover FOLL_SYSID = 12. Here is a part of my current code:
-- check key parameters
function check_parameters()
--[[
parameter values which are auto-set on startup
--]]
local key_params = {
FOLL_ENABLE = 1,
FOLL_OFS_TYPE = 1,
}
for p, v in pairs(key_params) do
local current = param:get(p)
assert(current, string.format("Parameter %s not found", p))
if math.abs(v - current) > 0.001 then
param:set_and_save(p, v)
gcs:send_text(MAV_SEVERITY.INFO, string.format("Parameter %s set to %.2f was %.2f", p, v, current))
end
end
end
-- update target position and velocity
function update_target()
if not follow:have_target() then
if have_target then
gcs:send_text(MAV_SEVERITY.WARNING, "No target")
arming:set_aux_auth_failed(auth_id, "Follow: no target")
end
have_target = false
return
end
if not have_target then
gcs:send_text(MAV_SEVERITY.INFO, "Have target")
arming:set_aux_auth_passed(auth_id)
end
have_target = true
target_pos, target_velocity = follow:get_target_location_and_velocity_ofs()
end
However, I am getting the following error:
3/12/2025 5:53:35 PM : Internal Error: ./scripts/servo.lua:134: attempt to index a nil value (global 'follow')
How do I properly initialize the follow object for the rover to follow the flying copter? Or Is there a specific setup or configuration required to enable the follow functionality in ArduPilot Lua scripting?
I would appreciate any advice or suggestions to resolve this issue.
Thank you in advance!
For a reason unknown to me, the devs have chosen to limit the follow binding to Copter or Plane.
@rmackay9 could perhaps elaborate on the rationale.
I don’t think it’d be problematic to simply enable the binding for Rover, but you’d need to set up a build environment and make the change yourself unless Randy or another dev see fit to enable the follow binding for Rover.
@Yuri_Rage Thanks for your response! I’d love to hear from other developers about why the ‘follow’ feature isn’t supported for Rover in Lua scripts, or if there’s a way to modify it to make it work more easily.
I don’t think that there’s any reason why we can’t enable this for Rover so I think it’s just a small change to add Rover to that list of available vehicles.
I could raise a PR to change that or anyone else could as well I think
P.S. I’ve moved this to the Rover-4.6 category instead of “General”
Thank you so much for your work! I’m currently using firmware version 4.5.7.
The reason I didn’t use Rover’s Follow mode is that I want the rover to move to a point calculated by optimizing the positions of several copters. To achieve this, I use a Lua script for control. Following a flying copter is simply a test case to validate the Lua script.
Regarding the Rover follow feature using Lua scripting — previously, I only tested whether follow:have_target() would return true, which worked fine.
Now that the official Rover 4.6 release is out, I’ve installed it on my rover to run the full follow behavior. However, I noticed that although follow:have_target() still returns true, other functions like follow:get_target_location_and_velocity_ofs() and follow:get_target_location_and_velocity() almost always return nil.
Occasionally, the target position appears once (as shown in the attached image), but most of the time it’s nil.
