I’m having some problems with the x-axis drivetrain (in other words the gantry). When moving the gantry, the belts become stuck underneath the V-wheels in the direction of travel. Please see the pictures below.
I have made sure that my x-axis tracks are straight - I have even removed the second track to only use one… I have checked that the gantry is square. I tried changing the orientation of the pulley to ensure that the belt runs vertically.
What is strange is that the y-axis movement of the z-axis assembly works perfectly.
Just my off-the-top-of-my-head thoughts:
1). Is it possible that the belt is twisted one revolution (or more) inside the vertical gantry beam?
2). Could the belt be tensioned too much? (too tight)
I loosened the tension of the belts and that seemed to fix the problem. I’ll take a video of the bot when I’ve hooked up all the electronics and post it for some more input.
@olafclarson
I seem to be having somewhat of the same issue.
My belt is riding up the side of the wheel much like your picture, but not as much.
Can you provide more detail on how much tension you reduced to, please?
A short video clip that shows deflection may be a easy way to show this.
Also, I am concerned that with all the “dialing in” of the FarmBot, I may have degraded the belt (lots of “slipping” in the early days), so I will order replacement belts ASAP.
I have a similar problem with my X-axis belts: After some distance of movement (about 20cm) they graually move to one side of the track and start rubbing at the sides of the v groove. That increases the friction a lot and also leads to wear.
I think the problem arises because the belts have slight imperfections and the left side has a little bit less flex than the right side. In the v groove they have room to twist a little and tuck themselves under the aluminium of one side. The problem was less prominent when the bot was new so I guess the fact that they get wet when it rains plays a role. After the belt ist offset to the right side it rubs against the right side of the track when the belt gets pulled towards the wheel. At first I dismissed this small misalignment as irrelevant but I think the increased friction is responsible for a lot of stalls during the movement of my X-axis.
I had the idea to print an alignment block which gets screwed down in between the belts. Any reasons why this could be a bad idea?
Any other ideas how this problem could be addressed?
Beside of that I’d check if the pulleys on the motors are centered in relation to the wheels. If they are not center to the wheels they can affect the centering of the belt on the wheels even while they are about 50cm away from them.
I installed my printed part on the left side of the gantry. At first glance it seems to work. I think I added some friction to the whole System because the plastic part slightly touches the wheel.
I increased the clearance to 0.5mm and the printer is currently producing the modified part for the right side of the gantry. If this works better I will reprint the left side as well. I will let you know when I have new results.
The new part is in use for four days now. It certainly increases friction but the motor is able to handle that. The problems with belts shifting underneath the wheels seems to be gone.
I would like the whole thing to have less friction overall because the Nema 17 motors are hardly able to move the gantry without additional breaks. Please let me know if you have any ideas for an improved part.
I like the 3D printed alignment block. It is a very good design.
The belts are wearing down because they may not be perfectly aligned in the track. You may need to slightly increase the tension on the belt and fix it in place so that it is located directly in the center of the gap in the track. Some of our users have glued the belts to exactly the center of the track.
Also, you may need to adjust the location of your X-Axis pulleys so that they are not pulling the belts out of alignment within the track.
Any deviation from the center of the track may cause belt wear.
In the cad design the belts are fixed with a kind of sleeve going around the two layers of interlocking belts. I was unable to find such a part in the FarmBot shop and also on any other machine parts onlineshop I checked. I previously had good results with zipties around both belts and I used this technique for my FarmBot. This generally works but as the zipties do not fit entirely inside the groove the belt is slightly raised at the first and last 5cm of the track. The Gantry wheels easily press the belt down into the track if they approach the end. But this movement might slightly change their position sideways. Maybe I should design a belt tensioner and endstop block which centers the belt more rigidly…
