Solidoodle Design Deficiencies (Page 1 of 2)

What needs to be changed in the firmware? Just move up to a higher rated (wattage) resistor, with same resistance?

Edit: I mean I see why they didn't move up, the properly rated one is $10 more, but you could use two 50W 6 ohm resistors in parallel and be within spec for only $3 more, and have more even bed heating.

@elmoret

You are correct, firmware tweak is only needed for a resistance change. Even if this happens it's only one value.

Sweet!

danny, I did the exact same thing. Im thinking that they should rotate that board 180 degrees to protect that cable. And whoever though that those electronics didn't need a cover is delusional (though that's apparently being fixed).

To me, the door is poorly done. The adhesive that held the magnet on was more effective than the magnet itself at holding the door shut, and both failed in less than one day. Also, the hole used to open the door looks incredibly cheap, and I feel like it should be replaced for a knob. This is a 100 dollar upgrade, they can spend an extra dollar to make it right.

Im still not sold on the Z-axis being 5/16-18 rod, but since I broke mine a week ago i haven't been able to further test it. This likely has cost repercussions so I wouldn't change it.

I think part of the solidoodles price point strategy is to produce a basic printing machine that works very well for the price, want a door knob .. print one, want an electronics case .. print one. I can see the amount of time it would take to print the larger parts like a electronics case would be better served printing required parts to get solidoodles out of the factory ASAP and fill the backlog. I would rather have a lower cost device I can print parts for in the colour I want than a more expensive one that I may have had to wait longer for.

My magnet adhesive also failed day one, though its not come off since, my case was only $50 though ? Considered a neo magnet but its not strong enough through the door and too strong if attached to the front of the acrylic.

Part of the fun of having a 3d printer for me is the upgrade process, this was made by hobbyists for hobbyists. Want a more complete machine there are plenty of $2000 options that may or may not print as well.

The USB cable, you need to remember its there and its all good, only move case back a small amount and lift. I agree it could be better protected .. again though its a printable solution. I was thinking of a small frame that screwed between the two board mounts and provided protection under the USB cable so the metal case will hit that before touching the USB cable.

see, now you have made me check your homework.. and you are simplifying the driver design decision too much. awfully impressive first post, i am sure made people feel disappointed in their device based on your opinion. heres mine..

pololu recomends the 1A max along with a max supply voltage of 35v. we are using 12v, the reduction in supply voltage by 300% should more than compensate an increase of current by 30% over a recomendation by a module maker.
the actual chip maker does not mention 1A anywhere, 32C/W on a 4 layer. how about hanging panelolu out to dry for not putting it on a 4 layer pcb as per manufacturer recomendations .. at the end of the day, thats all it is .. recomendations. no maximums have been exceeded anywhere.
You then build it, test it and base decisions based on how many units overheat, mine has never skipped a step yet that I know of. that would be a symptom of excess current, not a number in a pdf.

i would certainly chuck in fans to assist cooling though, probably add some sort of heatsink to boot if I go the rear cover.

resistor spec .. same deal, you are over simplifying the data, max rating is 50W at 25C .. big deal, that is a continuous power, it is regulated in this case, the power is not 50W but 0W well before resistor is compromised. not the same thing as 50W continuous, no where does the data state how the device is to be used, i am sure that having a PID controller and a thermocouple on it would make the manufacturers happy.
manufacturer specs are spot heat not to exceed 200C. they don't .. spec not exceeded.

. there is such a thing as over engineering something,  its not going into space or doing life support though, if it works .. do it.
What would NASA charge if they made this ?

disclaimer, I am not an engineer and do not claim to be. these are my opinions based on 40 plus years of professional electronics.

Plenty of people are seeing 100% duty cycles on the resistor to hit 105C. Then that is 48W at 105C, far beyond max spec. (50W at 25C). This has resulted in bed failures, at least 3 that I know of so far, in less than 3 months.

Pololu isn't to blame here, they clearly state that due to the PCB choice they made, they recommend 1A max. That is what I am operating off of, not the A4988's spec sheet. Not to mention there's half a dozen people that I know of with skipping steps unless the electronics are cooled. From Pololu's site:

These are being configured to draw 1.33A. That's beyond spec. Plain and simple. Pololu makes no allowances for supply voltage variation permitting more current.

It's just poor design, man. These things are being designed with factors of safety less than 1! How about the steppers being overdriven? No comments?

It's just not good engineering practice. I'd be fired in a heartbeat, even if it wasn't "for life support or going into space".

At the end of the day, the Solidoodle 2 could have been redesigned such that all parts were within manufacturer spec for less than $20 more. I for one would have happily paid that to know that everything was operating within manufacturer specifications.

the spec says 50W at 25C and mounted on a heatsink, well my ambient is about 25 and the resistor is on a heatsink (I would hazard a guess and say the build platform is around 1.5C/W.), operating temp is then around 105C max .. spec exceeded ? debateable, certainly not in the extreme way you are making out. its certainly at limits .. some having died is not a good thing, but I imagine those that fail are going to do so early though due to poor internal heatsinking of the resistor overheating a portion. If it survives a decent burn in period, it should be pretty trustworthy.

I haven't revisted the data .. but from memory the only thing the specs indicate regarding temperature is that spot heat does not exceed 200C.

the polulu driver say 'but to supply more than approximately 1 A per coil' .. seems a bit vague to me .. not really set in stone that one. As I said, mine has not skipped a step using the default settings, not twiddled any pots. not even looked at the currents. again .. at the limits but exceeded ?

not looked at the motor data yet .. i will later.

Yes, I have my printer.

Fix it by putting cooling on the electronics, upgrading the bed resistor once it fails so it doesn't fail again, using motors that are rated for the necessary torque, instead of overdriving smaller ones.

You are correct that the SD doesn't operate at 35v, but that does not mean you can push the Pololu controllers harder. Let me explain why.

The primary source of heat on the A4988 chip is from the mosfet on resistance. It is roughly 400mohms. The drivers modulate such that average current is whatever is specified, in this case 1.33A.

If you drive with a higher voltage, the power dissipated while the mosfets are on is greater, but the duty cycle is signifigantly less to achieve 1A average. Thus, heat dissipation is not a function of supply voltage. That is why there is no derating in the specifications with regard to supply voltage. It does not work like a LM7805 or other linear power chip. It works a lot more like a switching mode power supply. I can explain further if you are interested.

You are absolutely correct that one could print slower at less current. However, Solidoodle's own recommendations are beyond factory spec. So, if I desire to operate the product I purchased at the level for which it as advertised to perform, parts are being stressed beyond design max, over 30% in some cases. I feel like that is worth mentioning on a forum so people can be aware of it, and turn it down or add cooling if they so choose. It's worth mentioning also that Solidoodle provides no warranty, so when you smoke a bed resistor or A4988 or stepper motor down the road, you might be out of luck.

Something like adding more bed resistors, that's not a design deficiency, because it works as is, and will work indefinitely as is. No specifications were exceeded, and a tradeoff was made between uniformity and cost.

How about the manufacturer of the Sanguinololu specifically saying the traces are too small for heated beds, and SD putting the heated bed on there anyway without reinforcement in the way of jumpers? Ian's practically caught fire... You can't say this isn't a big deal!

Maybe it's just me. I know I couldn't sign off on some of these decisions, from an engineering ethics point of view, but maybe that's unreasonable. Who knows.

Don't get me wrong, I don't regret the purchase. I think it's great and I've enjoyed it a lot. I just think that with a little more thought, and $20/unit, it could be designed such that everything is within spec.

what I meant was:

If this thread is going to be repeating the same thing over and over and over. then there is not a lot of point in writing anything else.

Perhaps the 4layer board for stepper driver is something that they'll consider in future, but saying the same thing over and over isn't any more likely to make that happen.

exaggerating and saying that the machine nearly burned someone's house down won't make it happen either.

for the electronics, the only real advice is add a fan.
the bed resistor, kind of is what it is, not guaranteed to fail, in most cases not failing, but probably prone to premature failure.

What I meant was, if there is a problem then by all means let's suggest a fix, but getting fixated on one small part isn't really helpful to anyone.

Hey I was just reading through the A498 drivers but I think one 1 point was missed. Although the formula for current load is correct. The Full step mode limits the current to 70% of that

http://www.pololu.com/catalog/product/2128

So:
X axis: 1.11A
Y axis: 1.3A
Z axis: 1.25A
Extruder: 0.48A

is correct but that is then driving the coils at 70% in full step mode

X motor: .77A
Y motor: .91A
Z motor: .875A

so they are witihin the specs of the motor or close to the 1A. But the the A4988 is rated only to 1AM without cooling! so hence its over driving and full duty cycle should higher loads at the motor.

so they are not being over driven per-se buut right at max and with full duty cycle yes on hairy edge of motors.

and the boards are all at over limit without cooling!

So to clarify they did not totally miss the boat at 30% over load LOL