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cdsteinkuehler
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modmaker
I'm cranking op volume and the price has gone down from EUR 117 for the BeBoPr+ to EUR 84 already for a single BeBoPr++. When buying three boards the price is EUR 74 each. These boards include an accurate ADC to replace the crap version on the BeagleBone.
Great news, and those are great prices! Keep us all updated on the options for purchase, and I'll get my blog cape page updated if you send me details. Do you have any plans for a US distributor?
I'll start making announcements soon, first build up some stock. I don't want to sell vapour-ware.
No distributors yet. I intend to facilitate group buys via the BeBoPr forum. This way the shipping costs can be split and the best price can be reached. Anyone willing to take some stock is welcome though.
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cdsteinkuehler
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modmaker
Your BOM does not include prices so it's hard to make a fair comparison and people here seem to focus on PCB cost only.
My cost for one board right now is about $100 US, but that's parts only, qty 1, buying parts for one board from DigiKey ($70) with PCB from OSH Park ($26 ea), and probalby another $5-$15 in parts that I got sampled or have on-hand (the stack-through connectors and a couple TI parts). As I mentioned to someone else, at this point buying a pre-built BeBoPr is still the best way to go (and could easily continue to be). If I was selling boards (and I don't plan to), I likely wouldn't be able to match your 117 EU for assembled units, much less the 84 EU price of the ++, certainly not without getting into buying lots for 50-100 boards at a time...and I don't want to get into the board business. I honestly did this design as much to test out KiCAD (it's workable, but _painful_ to use for production designs in it's current state) and run some larger boards through OSH Park and some off-shore vendors as anything else.
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modmaker
What complexity do you mean exactly? I see original BeBoPr features being integrated in the latest RAMPS designs (E.g. mergency stop and analog input protection), so RAMPS seems to be getting more complex with each new design.
Yes, the CRAMPS (and the RAMPS-FD it's based on) are more compelx than the inital RAMPS board (which was mostly just a PCB with various connectors), but it is still simpler in design than the BeBoPr or Replicape. Specifically, I'm referring to things like:
5V power: This is provided by the BeBoPr/Replicape, but the CRAMPS requires you provide 5V to the BeagleBone or populate a header with an optional 5V regulator module.
I think it's part of the charm of the BeBoPr that you need only one supply. And now that you can use anything between 12 and 24 Volts it's even more attractive. The original Replicape did not have this feature and it was added later, so I'm not the only one seeing the benefits. But I agree that it's probably 'too complicated' for the average RAMPS design(er).
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cdsteinkuehler
FET Drive: The CRAMPS/RAMPS-FD uses the same logic-level FETs with 5V drive as used on the RAMPS. I've never much cared for this solution and it means more expensive FETs and larger packages to dissipate the resulting heat from not using a 10-12V gate drive. But the RAMPS-FD folks didn't like my "poor-man's" FET drive suggestions, and I'm sticking with the 74ACT drivers they settled on. They are readily available and inexpensive, the only drawback is the 5V gate drive. :-/
Initially I thought that the cheap logic level design would suffice too. But heat could cause a problem in situations where people were not careful enough. That's why I re-designed the PWM output stages. The BeBoPr++ is now capable of directly switching a 10A load (e.g. a HBP) higher without burning the FETs from the board. The thermal picture below shows the BeBoPr++ switching 10A at 40 kHz (98% duty cycle). At this frequency the temperature rise of the FETs is around 22 degrees C above ambient, of which 5-6 degrees is caused by switching losses. The fuse is by far the hottest component in the area, but that one is meant to self destruct X(
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cdsteinkuehler
I/O Protection: The CRAMPS does what I would classify as minimal protection. It should be possible to hook 5V signals up to some pins, but overal it will be much easier to fry your BeagleBone using a CRAMPS board than a BeBoPr.
Frying the BeagleBone is less of an issue since the BBB. It's so dirt cheap, at least if you can get one :X
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cdsteinkuehler
ADC: As you mentioned, the on-chip ADC on the BeagleBone "lacks performance" :) The CRAMPS design uses the on-chip ADC (and inherits all the noise and other problems that brings with it), and has what I would define as minimal input protection. I'd feel much better with op-amps in the circuit, but those cost money and aren't on the RAMPS-FD BOM (another goal is to try and get some RAMPS/RAMPS-FD vendors to build the CRAMPS too, so having a very similar parts BOM is important...I don't want to get in the building boards business).
I've been testing and packing a batch of BeBoPr++ boards now. Is a pleasure to see these ADC values after all the troubles with the BeagleBone's ADC. I'm now getting stable and reproducable measurements on all the boards. Not even a single bit of noise. The BeagleBone's ADC is now free to use for a touch-screen, as was probably intended. I think TI can do a better job and fix the driver, but maybe they have a silicon problem and this will be all we get. Most micro-controllers ADCs perform much better.
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cdsteinkuehler
Overall, I see room for a spectrum of products. There are several low-cost CNC capes available, I did the CRAMPS board because I'm hoping it can fill this segment for the 3D printer folks. The next step up would be a board like the BeBoPr++ or Replicape, followed by something like an FPGA daughtercard (none are currently available, but a few designs are in the works). Note that my perspective is focused on using LinuxCNC as the control software. I know you have your software, and Elias has something he's using with the Replicape (I honestly have yet to test out either...I should do that sometime!). Choice of software can dramtically affect the decision of hardware to buy...for instance the BeBoPr is the *ONLY* board currently supported by LinuxCNC. Even my CRAMPS design doesn't have any working example configurations yet, and it will probably be some time until the Replicape is supported, since it requires use of various hardware interfaces (I2C and SPI controllers) I haven't written LinuxCNC HAL drivers for yet.