Z-axis issues, Express: heavy fall, stuttering, stalls

kegli · March 12, 2021, 4:33pm

I am trying to get my Express to work out of the box. I’ve spent some time now trying to get the Z-axis to function properly [Y works great; X is close but I’m going for one thing at a time here.]

The hardware on the Z axis is struggling to say the least. Sometimes it can move mostly up or down, but never all the way. The load is quite high and seems to be labouring.

One issue is just that in neutral, non functioning mode, the whole Z axis can sometimes just…fall? It spins with gravity right to the bottom. So I tighten the wheels and check the spacers, whether tightened or loosened, it still happens.
In both up and down directions, it will occasionally do a 3 move stutter and give me a relative movement error. Not always, but sometimes.
If it ever actually moves more than say 300mm without a stutter, it sure sounds like she’s struggling. Like the motor can’t handle the weight.

Thanks for your time, I’ll listen to any advice.

kegli · March 12, 2021, 4:35pm

zload

RickCarlino · March 12, 2021, 6:29pm

@kegli We have a feature called “Always Power Motors” to solve this problem. The reason this happens is that the weight of the Z-Axis is enough to pull the axis to the ground over time. By applying power to the z-axis at all times, it is possible to resist gravity:

Rory or Marc will reach out to you soon with regards to the other issues.

kegli · April 21, 2021, 2:26pm

Rick, in my picture above yours you can see I have it on as well.

Esbenman · May 18, 2023, 9:29am

I have the same problem, is there a solution to this?

kegli · May 18, 2023, 1:35pm

It was a while ago. I was lucky enough to have the FarmBot team video conference with me and solve some problems, but the gist of it was:

There was a lot of tinkering to get the exact current and speed for the motor to limit load
I was instructed to use a graphite lubricant (Jigaloo) on the main Z screw (this was pretty messy)

Capture439×528 40.5 KB

Esbenman · June 13, 2023, 7:51am

Thanks a lot! I wonder why it has to be so difficult, seems the stepper motor is not the right one for the task. I have not gotten mine to work yet, I also most of the days I have time to look at this problem run into problems with the message broker not connecting, and then I cannot operate the robot.
Thanks again!

ranguard · October 28, 2023, 9:59am

Having tried several things with the Farm bot team (very helpful) the best setup for express z-axis seems to be

Motor always powered…
Stall detection off for day to day operations
Stall detection on for find home (but currently no UI way of doing this)

Ideally I want the find home to happen at boot, but the closest I could get was to create a lua sequence which runs periodically as part of other sequences…

See code / docs / limitations (e.g env values existing between reboots) at:

jsimmonds · October 30, 2023, 7:33am

Hi @ranguard
In your sequence which runs on boot you could use the provided Lua function find_home(axis?) which performs “find home” on a specified axis.

From the FarmBot docs =>

edit

I’ll try to find the easiest way of turning axis stall detection ON or OFF

ps

If you didn’t know about the “Seqence-On-Boot” feature in FBOS, here’s where to find it

ranguard · October 30, 2023, 1:24pm

Hi @jsimmonds,

Thanks for the reply…

I have code to find_home and enable / disable stall detection:

github.com

ranguard/farmbot-leo-utils/blob/main/sequences/find_home_periodically/find_home_periodically.lua

function shouldSkipHomeCheck()
    local time_check = env("HOME_CHECK_AFTER")
    -- toast("shouldSkipHomeCheck time_check value = " .. time_check)
    if time_check then
        -- has the time check expired?
        local now = os.time();
        if now > tonumber(time_check) then
            return 0
        end
    else
        -- It was not set previously so run now
        return 0
    end
    -- Assume we are skipping the check
    return 1
end

function runHomeCheck(zStallMax)
    send_message("info", "Running home possition checks", "toast")

This file has been truncated. show original

But I didn’t know about the sequence-on-boot! - though interestingly that seems to not allow sequences with variables (even with default values)… but I can hard code those - so this is great thank you.

ranguard · November 3, 2023, 11:48am

I’ve updated

There is now one version that can be run at boot time and another for periodic checking.

I can’t publish this as a sequence for others as it contains Lua - but happy for it to be made available
by farmbot team if they feel of use