I'm interested in Buwizz PCB and components. Can someone share good photos of the Buwizz PCB (both sides)? It will be very cool to see Buwizz 2.0 but older versions will also be good.
5@mindstormsboi This community isn't solely focused on official LEGO elements. From the tour page: "we're working together to build a library of detailed answers to every question about LEGO bricks and compatible building systems"– jncraton ♦May 31, 2020 at 19:38
@jncraton Nevermind, should've googled before flagging.– mindstormsboiMay 31, 2020 at 19:40
I don't have this part, so I can't directly give you the photos that you are looking for, but there is at least one teardown video floating around that we can use to see what is inside the BuWizz 2.0 module.
The module contains 2x 850mAh LiPo batteries:
The top of the PCB looks something like this:
I wasn't able to find an image showing the back of the PCB
System on a chip
From the above images, we can see that the main microprocessor is a Cypress PSoC 4200 series. Looking at the datasheet, we see that is a BLE-enabled system on a chip running at 48MHz with 128KiB of flash.
There are at least 4 DRV8833 chips present on the PCB. This chip is a dual H-bridge. The datasheet for the part indicates that each channel can handle 1.5A RMS/DC or 2A peak. The specs for the BuWizz indicate:
- Max continuous current per channel: 4 A
- Max instantaneous current per channel: 6.5 A
- Max continuous power per channel: 36 W (HIGH speed mode)
- Max instantaneous power per channel: 55 W (HIGH speed mode)
- Max total power: 45 W
- SLOW: 5.2 V
- NORMAL: 7.2 V
- FAST: 9.2 V
- LUDICROUS: 11.2 V
I'm not sure how 4A per channel is achieved safely using the DRV8833. Given that 4 dual H-bridges are included, it is safe to assume that each chip is driving each output using both H-bridges in parallel, but according the the datasheet, this still only gets us to 3A RMS/DC per channel.
My hunch is that they are simply driving these parts harder than intended. We can see that they are using them at 11.2 volts, while the datasheet recommends a max operating voltage of 10.8 volts. It's worth noting that the max quoted continuous power per channel (36W) is very close to what you would get from a parallel configuration running at 11.2V (11.2V * 3A = 33.6W).
The BuWizz has carved out a niche for itself by going well beyond recommend operating power (the LEGO PF battery box tops out at 9V * .8A = 7.2W or less than a quarter of the BuWizz), so I wouldn't be surprised if they are running the motor drivers a bit hot.
Thank you very much! I already see this video, very useful but I am very interesting on their power supply components. They say in specs: 4A per channel, 6.5A MAX per channel - I want to know how :) Motor drivers is popular DRV8833 Jun 1, 2020 at 6:58
1@AloyanDmitry That makes sense. I've updated my answer with some thoughts on the motor driver specifically.– jncraton ♦Jun 1, 2020 at 14:38
Thank you for detailed update. It is very useful! But I talking about DC-DC converter used on this PCB. So, as we can see dc-dc contains one inductor (222 squire). Inductor is small and use about 1MHz (not sure). Bigger frequency require smaller inductors, but we talk about Boost converter from 3.7-4.2v (in battery) to 11.2v 3A = 33.6W so inductor for 33.6W should be bigger. So if we load 2-3 channels we got only 1A or 0.5A per channel. My decision: this device can give 9v 2A max (and only to one channel per time), in 11v current will be less Jun 1, 2020 at 17:02
@AloyanDmitry That's a good point. I don't know enough about this stuff off the top of my head to speak to inductor sizing vs frequency vs power here. However, this device does include 2 LiPo batteries, likely to be used in series, so the nominal voltage may be ~7.2 volts. The battery voltage may be used directly for the motors in "normal" mode.– jncraton ♦Jun 1, 2020 at 19:27
As we see, in PCB only 2 battery polygons, it mean they connected parallel and don't have any balancing staff (like in BMS boards). Using 2 batteries without balancing is too dangerous (we talking about kid toy (yeah kid... ha ha... all know it not for kids :D)) Also buwizz use usb charger and we don't see any additional converter from 5v to 8.6v (2 lipo in serial give 8.6v). All talking about parallel connection. Also, if some one interesting, I working on OpenSource/OpenHardware controller for Technic wibrick.wilix.org Any help are welcome :) Jun 2, 2020 at 17:00