ORD Bot heat bed problems

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ORD Bot heat bed problems

Postby Tomas1337 » Thu Feb 28, 2013 9:15 am

Hi, guys.

We've been building our ORDBOT for quitesome time now and have encountered numerous problems, but we've got the hang of most of them already. Now I'm stumped. My prints almost always warp and lift! Even if what we're printing is fast and small. One suspect is the draft but I've somewhat enclosed our printer already. I think its the heatbed not getting hot enough and then not maintaining its temperature. My heatbed takes a long time to heat up can only rise to around 100C (I'm using ABS) and when the print starts it goes down to around 80 or even 70. I think this temperature difference is a major factor in the warping. Is there a problem in my heatbed? or power supply? I have a 12W 300W Powersupply that came with the kit.
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Re: ORD Bot heat bed problems

Postby cvoinescu » Thu Feb 28, 2013 11:54 am

Measure the voltage directly on the heated bed terminals, and on the controller terminals, and on the power supply, to determine where the drop is.

(Personally, I think that trying to handle 10-12 A is too much trouble, and that it would be so much simpler to switch everything but the fans to 24 V.)

Do you have a fan? Is it cooling your heated bed? Can it be turned off? For ABS, you don't need a fan on the print, except perhaps for bridges. If your extruder needs a fan, make sure it doesn't cool the heated bed (add a baffle or something like that to redirect the airflow).

You can add insulation on the underside of the heated bed to help it heat up faster. At a bare minimum, there should be an air gap there, but insulation helps a lot.
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Re: ORD Bot heat bed problems

Postby bdring » Thu Feb 28, 2013 1:22 pm

I second the recommendation of checking the voltage at the bed while it is on. If you use a thinner wire gauge, you might have a large voltage drop across the wire. The wire will get warm too.

Does you power supply roughly look like this one?

$T2eC16Z,!zEE9s3!YlV+BQfQgBEFgw~~60_3.JPG


If so try adjusting the pot until you see about 12.5V on the terminals of the bed while it is on.

I added a note on this to the Wiki
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Re: ORD Bot heat bed problems

Postby Tomas1337 » Fri Mar 01, 2013 11:05 am

Hi, guys.

Thank for the replies and suggestion.
I've measured the voltage at the heatbed terminals and they're at 12.95V but still not getting to the right temperatures and not staying at a set temperature.

I do have an extruder fan and I will do the suggestion of adding the baffles for the redirection of the airflow.

Also, I have added silicone pads underneath the heatbed with a small airgap in between. It helped, but not so much.
And yes that is my power supply as seen on the picture.

Could a factor be my software? I'm running on Sprinter but almost everyone here I see is using Marlin.

Thanks guys. I really appreciate the help. Almost coming to 4 months of this thing! :)
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Re: ORD Bot heat bed problems

Postby Zat German » Fri Mar 01, 2013 12:08 pm

What heated bed do you have?
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Re: ORD Bot heat bed problems

Postby bdring » Fri Mar 01, 2013 2:03 pm

The firmware does not matter, assuming they are setup the same. I would suggest bit-banging rather than PID. PID will hold the temp closer. Bit-bang should be within a few degrees. Bit-banging will make sure it stays on full until it reaches temp.
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Re: ORD Bot heat bed problems

Postby brnrd » Fri Mar 01, 2013 5:33 pm

Some details on the heat bed would help. I suspect that the resistance might be too high resulting in not enough power.
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Re: ORD Bot heat bed problems

Postby Tomas1337 » Sun Mar 03, 2013 11:43 am

The heatbed that came with the kit is a LAVAL HBP v1.0
I have gotten it to reach 110 within a few minutes. I did this by removing the target temperature in the gcode and just set the temperature on the pronterface console.
Prints still lift though.

My investigation so far has lead me to think that the primary suspect is the airflow of the extruder fan. I put a small string of cotton below the hotend and turned the fan on. The air of the extruder fan kept pushing it out of the way.
The other solution I thought was to take out the extruder fan completely but that only lead to my extruder getting jammed. I think I really need to create an enclosure and isolate the airflow to the hot end.

Thanks for the suggestion guys! I'll update you as soon as I can
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Re: ORD Bot heat bed problems

Postby brnrd » Sun Mar 03, 2013 5:34 pm

I don't know that heat bed. But, the important thing is the resistance of the bed. Then you can calculate how much power you're able to put into it (V^2/R). Depending on the temperature of your room, you need around 130 W for ABS.

I suggest trying to tackle the problem in a steps instead of trying to diagnose it by printing test pieces. First, turn off the extruder fan and set the bed temperature in proterface to 110C. Does it reach a stable reading? Are you sure that the surface temperature of your bed is the same as the thermistor reading? This can be off if your firmware is set for the wrong thermistor. It also will usually be off since your thermistor is probably not mounted on the surface. If you have an IR thermometer, you can use it if you put tape (blue tape works) on top of glass, if that's what you have. You might need to set you bed to a slightly higher temperature to account for the difference.

Then, turn on your extruder fan and see how much your bed temperature reading drops. Also, monitor the voltage from your power supply and at the heated bed terminal through the process. Since you mentioned that the bed temperature drops to 80C when the extruder fan is on, it can also be due to a voltage drop in addition to the air flow.
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Re: ORD Bot heat bed problems

Postby bdring » Sun Mar 03, 2013 5:48 pm

Is it the blue Lava bed?

I have a couple early versions and they have a lot of trouble reaching temperature. I don't use currently use them. I think the resistance is too high on them. Crank up the voltage about another volt :)
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