Is Ramps / Arduino / Polulu's - Fragile?

Hi,

Looking at the forums it would seem like the RAMPS system is a bit sensitive or fragile.

Do you need to handle these electronics "extra" cautiously, or is it just a few isolated issues arising in the forums?

It won't change my selection as I already have components, (must wait for x-mass to assemble).

Any thoughts...

Rich

Pololus don't like having the motors plugged in or removed with any power to the board.
I've personally never lost a driver on 3 ramps boards, but if you start mis-wiring things all bets are off.

I'm interested in what you perceive to be the the fragility?

Posts kind of like these.....

shorted stepper driver by finger?

X axis motor not moving under RAMPS 1.4 test firmware

This might just be a perception as I noted....

It's exposed electronics, and there is nothing to stop you plugging things in wrong, so I guess compared to your average off the shelf electronics component, it's fragile.
From what I see, most of the failures from known working boards are people miss wiring, shorting things, or disconnecting/connecting motor wires with power (either USB or external).
Though there were a few Chinese sourced pololus reported to burst into flames.
I certainly don't think the RAMPS/Pololu combination is any more "fragile" than the alternatives.

I don't think RAMPS is fragile.

There are a few design decisions that cause issues, and a few general issues (with many types of electronics, not specific to RAMPS) that cause confusion.

1. PTC Polyfuses.
I think anyone reading this forum by now knows of my hate of the PTC polyfuses. To summarise: The 11A polyfuse isn't always up to the job (some beds draw close to 12A), and tops out at about 16-18V (useless if you want to run 24V heated beds). They generate a HUGE amount of heat when near their operating current, and if they're touching at all, one will trip before the other due to the combined heat (they work on heat and each current limit trips at a different internal temp). In extreme over-current situations, they can actually catch fire (I have seen this first hand - put 12V @ 24A through an 11A polyfuse and watch it catch fire), which isn't protecting anyone! Car blade fuses (on board, like RAMBo does) or in-line fuses in the cabling are a much better solution.

2. Output screw terminals (D8, D9 & D10).
The standard (el-cheapo) screw connectors have 3 main failings: A. The generic connectors have a tendency to fail after a small number of uses (if they're going to fail). B. They usually aren't designed for the high current of the heated bed. C. When doing them up with a screw driver, you can easily apply too much torque to the connector and bend/break a pin that solders to the board, which can lead to an intermittent connection. On the boards I've done, I've hacked in the same connectors used for power (the screw terminals with the quick disconnect connector built into them - which are specced on the original electronics, but not on some of the cheaper ones where they sacrifice quality for cost). Required me filing the edge off a connector body to get it to fit. Using the same connectors as the power connector means you get the option for quick-disconnect as well, which is useful when debugging. Changing this properly (so there is no hack) requires a small change to the connector pin locations on the PCB to avoid them interfering with the power connector.

3. FET's.
The standard STP55NF06L FET's that were on the original electronics are just not quite up to the job of running the heated bed (the high-stress case). IMO the FDP8870's or the IRLB8743 are a much better choice. FWIW: Looking at E14 here in Australia, the IRLB8743 is actually 4 cents cheaper than the STP55NF06L's in 1-off qty's, so it no longer makes sense to use the older FET's even on a cost comparison basis.

4. Capacitors.
If you decide you want to assemble/solder your own RAMPS, then you will most likely find the capacitors are the hardest to source part. Here in Australia, we had a huge issue and eventually had to order them from Digikey (neither E14 and RS have them in the values needed). They also don't like a lot of heat, so using the "toaster over" method of SMD component soldering can lead to them exploding. We ended up hand-soldering them after doing all the resistors/LED's in the SMD oven. Personally I'd like to go back to through-hole caps, which have fewer issues.

5. Motor cables.
The placement of the motor cables is a pain in the rear, coming from the centre of the board. Add to that the annoying standard pin header connectors (see more below) and it leads to all sorts of issues, plus makes it annoying to cool with a fan (cables in the way of airflow).

That's the RAMPS specific stuff. Onto the more general stuff.

A. Pololu's.
They're OK as long as you don't abuse them. They do need adequate heatsinking, and to get that you really do need a fan on it. The whole board design does not lend itself to really good heatsinking though. I personally use Arctic Alumina Thermal Adhesive to glue on my heatsinks. It's not that cheap (I found some for > $8 US), but the 7ish grams you get goes a VERY LONG WAY. I use the Alumina one as it's not only non-conductive, but non-capacitive. Also, as others note, do not remove the connectors to the motors while power is applied. I replace all the motor connectors on the PCB with Molex locking connectors, to avoid the motors being disconnected accidentally. They use the same type of pins on the PCB, but have a locking arrangement on them. You have to cut off the old connectors from your cable and replace those, but IMO it's worth it. I list that here, as MOST Pololu boards I've seen do not have locking connectors on the motors (not just RAMPS), so it's not specific to RAMPS at all. FWIW: It's even possible to rip the plastic shroud off the locking connector and the standard pins you have on the PCB, and just put the locking part on the existing pins (no desolder/resolder of the PCB pins). I might post some pics later about how to do it if people are interested.

B. Power supplies and power loss.
This applies to most electronics. The decision to use 12V (which does have it's reasons, notably availability), especially for the heated bed, tends to cause problems with current. Anything high current (eg: Heated bed) leads to a large power loss due to cable resistance. Without changing the voltage, you need to use fairly large/thick or high quality (and therefore expensive) cabling to avoid it. Using a higher voltage like 24V for the bed reduces the current for the same power (1/2 the current for 24V), and leads to much less power lost (between the board and the PSU, between the board and the heated bed, and across your output FET). JohnnyR made the right decision early off to run a separate supply input for the heated bed, but then stuffed things up by putting in that stupid polyfuse, which can't handle 24V. Added to this a lack of 24V options for heating your bed (no PCB heated bed for sale that does 24V AFAIK, so the MendelMax stick-on heated bed element for 24V seems to be the only real option at the moment short of making your own).

That's most of the issues IMO. There are probably a few more but this is just off the top of my head.

Wow Cefiar,

I was not trying to get you or anyone fired up...
I have the RAMPS 1.4 board (waiting for x-mass), and was trying to get a feel for the issues.
It seems that you have most of these listed.

Do you like the board?

Richard

Well I use RAMPS on a number of machines. Two of them is are 1.2a boards, and the rest are 1.4 boards. If I didn't like the basic idea, I wouldn't be using them.

I'm hoping to get some free time over Christmas and "hopefully" get around to designing a slightly larger, more friendly version of RAMPS. Plan is to stick to pretty much the same schematic, same pinouts (if at all possible) and similar aux I/O pinouts so that expansion devices (like SD Card adapters) don't need to be "re-engineered".

Basically something sort of half way between RAMPS and RAMBo (which has the Mega as part of the board). Also want to spec decent parts. IMO this is one of the things that hurts RAMPS the most, as while the 'cheaper' parts work say 90% of the time, it's the 10% that have problems that cause real frustration.

I'd rather spend the $3-5 more, and know that I won't have to deal with anywhere near as many issues.

Cool,

Thanks for all of the comments.

I am hopeing that I will be running by January.

Richard

Quote
Cefiar
I replace all the motor connectors on the PCB with Molex locking connectors, to avoid the motors being disconnected accidentally. They use the same type of pins on the PCB, but have a locking arrangement on them. You have to cut off the old connectors from your cable and replace those, but IMO it's worth it. I list that here, as MOST Pololu boards I've seen do not have locking connectors on the motors (not just RAMPS), so it's not specific to RAMPS at all. FWIW: It's even possible to rip the plastic shroud off the locking connector and the standard pins you have on the PCB, and just put the locking part on the existing pins (no desolder/resolder of the PCB pins). I might post some pics later about how to do it if people are interested.

I would be interested to see how you do this.