:) Exactly what I've done some weeks ago, but only 2 notes, remember? You even said you could raise the PWM frequency to cover 2 or 3 octaves.
I've used a 4 Ohm lamp. It could be a 4 Ohm loudspeaker, like those used in cars. 16 W RMS. Or more usual 8 Ohm loudspeakers, 8 W RMS. 2 SBrick ports and you have 2x8 Watt, quite a lot of noise if inside a room.
First of all, there's no need to worry.
Both the SBrick and the IR receiver drives the motors with PWM or Pulse Width Modulated voltage.
Both devices work by turning the voltage on and off once in about every thousandth of a second, so in each cycle the motor is on for some time, and off for some. The more the motor is on, the more torque and power it can deliver.
Certain parts of a motor can vibrate, and give off a tweeting sound that is the loudest when the motor is driven with 50% duty cycle e.g. it is on for 50% of the time.
We did our best to support LEGO's M motor, and we did great, since we can drive more M motors per channel than the IR can, and the overall current carrying capacity of the SBrick is much higher than the same figure in case of the IR receiver.
This alsomeans that SBrick might turn on the motors more quickly than the IR recever, and therefore the noise might me louder.
Moreover, the IR receiver only applies PWM duty cycles other than 0 and 100% (where there's no noise, but this is the case with SBrick too) if you use it with a 8879 remote.
Additionally, SBrick can utilize 255 PWM levels. The first 20-30 levels are not really useful with PF motors, since they won't even start. At these levels, there is no motor noise to cover the beeping. Once the motors are running at a reasonable rate, their noise usually masks the tweeting.
If you're really annoyed by the noise, I can do a few experiments to either lower the PWM frequency (lower sounds are harder to radiate, and are masked better by the motors), or increase it (with a bit of luck, above the ~20 KHz limit of the human ear). Since this can affect power efficiency (higher the frequency, higher the switching loss, there's more heat), such parameter should be allow tweaking (let the user to override it).
(Hm, I've looked at the code, and the lowest frequency is about 490Hz, the highest is well above 100KHz. DRV8833's rise and fall time is 160 & 180ns, so it might be able to work at that frequency.)
The SBrick can withstand 3A in one port. Thats for sure.
And it can also withstand a total intake of 6A, my last video shows it at 5.7A
But in middle is not so linear... my last video shows SBrick driving a resistive load of 4 Ohm at each port. With my battery, that should mean 2A per port. Just one port: yes, 2A. Two ports: 90% (1.8A each) of that. 3 ports: 80% (1.6A each. And 4 ports: 70% (1.4A each).
So you want 2x1.8A continuously? Yes, you can. You want 2x1.6A with some peaks up to 2A simultanously? Yes, I think you can, perhaps even more. You want 2x1.6A with some peaks up to 3A in ONE of the ports? Yes, you can. But 2x2A continuously... I have my doubts.
Had you considered 4 L-motors? They stall at 18 N.cm with 1.3A so 4xL equals 72 N.cm and 5.2A... and more rpms.
Thats an interesting explanation, and good thoughts......... thanks!
A 2 cell LiPo is probably the best solution. If I build "light" enough 2 XL motors maybe do the job.
I just tend to build very sturdy, and therefore my models get too heavy most of the time.
Gearing down 3 : 5 would help for the torque........sacrificing the already poor rpm of an XL motor.
So the sbrick can withstand up to 2A at each port you would say? Or at least at 2 ports...
4 XL + 1 Servo? Like 2 XL in 1st port, 2 XL in 2nd port, servo in 3rd port and 4th port free or for liights?
Philo says each XL consumes 1.8A @ 9V when stalled (but also a 40 N.cm torque, almost all you need).
It's not easy to stall a XL motor. If you use 2 XL in one SBrick port and 2 XL in another port you might just need 2A in each port, 4A total.
Both the rechargeable battery and the battery pack have an overcurrent protection (around 0.8A). That's way both seem «just too weak». There are people modding their batteries to remove the protection but that's dangerous (at least with the PF LiPo batery) because it's a small battery and probably not suitable for high current demans.
You could also:
- connect several Power Functions batteries/battery packs in parallel (if you use 2, each one cuts at 0.8A but you get 1.6A). But for 4A you'll need 5 batteries, that's quite a lot
- use a 2-cell LiPo or simillar RC battery (~7.4V) from RC Hobby Shops, they can withstand very high currents (mine is just 1500 mAh but can withstand 37.5 A!)
Please note that although it's possible to use one SBrick with 4A that's quite a lot. A better option would be to use 2 Sbricks (I don't receive money from Vengit :) ) and put one XL in its own port - you end with 3 unused ports but you'll get better power and thermal distribution. You can use the same 2-cell LiPo battery, just split power cables with an Y.
Thanks, for the fast answers.
I need to power 4 XL motors for propulsion (hard-coupled with knop wheels, for 58 Ncm torque)
and a servo motor for steering......... and was thinking of a "stronger" power source.
The rechargeable battery from Lego is just too weak, and the 9 Volt Battery version is a hassle to get out the AA cells for recharge.
If anyone has a good power source solution for the sbrick with 4 XL motors let me know :-)
By the way, when will the sbrick App for windows phones be ready?
Yupp, a 3-cell LiPo will probably blow the SBrick when it's fully charged.
Howevet more voltage doesn't necessary means more dissipation inside the brick, since the motor drivers are MOSFET switches. They are either turned off (zero current) or on (very little voltage drop). The switch time and therefore the dissipatoin during switching ARE dependent on the voltage though, but I don't think that's significant.
The two things that will likely kill your bricks are:
- Overvoltage
- High current for a long time period.
The latter seems strange, since the SBrick does have overcurrent protection, AND protection from thermal runaway.
But if you would run your brick just under the OCP level (probably on multiple ports and / or powered from the bottom C1/C2 pins (the ones with diodes)), the electronics could heat up, and soften or melt the plastic, since the glass transition temperature of ABS (105°C) is lower than the overtemperature protection in the DRV8833 drivers (150-180°C, 160 typical).
Be careful with high currents.
To aid hacking & developing unusual applications, the new firmware will contain a thermometer function and customizable thermal protection.
[blockquote]Stefan H. said:Can I connect the sbrick to a 3 cell 11,1 Voltage LiPo Akku (as power source) without harming it?[/blockquote]
You shouldn't. A full charged LiPo shows slightly more voltage than is "nominal" value - in my latests "SBrick Heavy Load" videos I've used a 2 cell 7.4V LiCoO and it shows 8.2V when fresh.
If you're going to use less than 3A overall, you can add two 1N5401 diodes to your 3 cell battery so you drop 1.3 to 1.6 Volt (and up to 5 Watt!).
There's also another issue: heat. The reason you want a 3 cell is also high current, right? 11V x 3A = 33 Watt, 11V x 5A = 55 Watt. You risk toasting your SBrick.
Hello,
I just got my first sbrick by mail. Can I connect the sbrick to a 3 cell 11,1 Voltage LiPo Akku (as power source) without harming it?
Thanks
Cheers
Steff
I tried to get some statistics here:
https://social.sbrick.com/forums/topic/68/device-sbrick-connection-compatibility-statistics
But here on forums there is just a subset of owners (maybe 40? while just play store lists 500+ installs) and only a subset replied (thanks there), so there is not a big variety.
In the last KS newsletter or somewhere here there was a mention of planned bug report for the app, but that might be quite some time in future and still will only voer people with specific issues.
My suggestion would be to create a online survey (using free sites or own homepage) with few question about the app and connectivity and distribute it through the newsletter. To motivate people one could use some reward, like a set of professionaly made profiles for future profile maker.
[blockquote]Technicmaster0 . said:But better good hardware than good software. The software can be updated, the hardware can't.
The people just have to be more patient. This is a kickstarter project. It was almost clear that not everything would work as expected.[/blockquote]
I agree that it's a good thing it is the software and not the hardware for exactly the reason you specify; the software can be updated.
However, as far as I recall there has not been much information shared about the software and its possible issues. The Kickstarter information suggested all was fine and good to go, the information on the hardware was extensive and decent feedback was given about the molds, tests, orders for the chips, et cetera. But for the software no limitations were suggested except for the fact that the beta mobile apps were released to the app stores in November. To quote from the Kickstarter emails: "The IOS app beta is already available in the App Store and is called SBrick; ;) The Android app beta will be out in November, with Windows following hard on their heels in December."
Personally I would expect from Beta software that I can at least work with it a bit. Sure, it may have glitches, it may crash when you do certain things. It may show some unexpected behaviour. But as several voices have already stated: users are stuck at the point they can't use it at all. All the additional features which it might have become worthless if you can't connect to the Sbrick as that is the superlative of "It was almost clear that not everything would work as expected."
But you are right, we have to be more patient. I'm confident that in the end when all these teething issues have been resolved it will be an amazing product altogether.
[blockquote]Jeroen Stap said:
In my opinion it seems that the KS project has been undertaken with great knowledge of both HW and SW, but the team has underestimated the SW development trickeries when it comes to supporting things on a wide variaty of devices. Also, as soon as the HW was delivered, everyone´s expectations were raised: "the HW looks great, why isn't the SW of the same quality?" It´s really frustrating to have the device in posession for a while now without being able to use it at all.
I would like to see a page where users could check and perhaps also update their experiences per device, in order to get a clear overview of what works and what doesn't.
[/blockquote]
But better good hardware than good software. The software can be updated, the hardware can't.
The people just have to be more patient. This is a kickstarter project. It was almost clear that not everything would work as expected.
In my opinion it seems that the KS project has been undertaken with great knowledge of both HW and SW, but the team has underestimated the SW development trickeries when it comes to supporting things on a wide variaty of devices. Also, as soon as the HW was delivered, everyone´s expectations were raised: "the HW looks great, why isn't the SW of the same quality?" It´s really frustrating to have the device in posession for a while now without being able to use it at all.
I would like to see a page where users could check and perhaps also update their experiences per device, in order to get a clear overview of what works and what doesn't.
The HW seems solid, but only time and hundreds of Wh passed through it will tell ... and this is the best news (together with option to run in with 3rd party apps - like nRF control panel)
The compatibility with broad scope of different devices is always a challenge - we have a product at work that 'should' run on most current devices and its a never ending fight. Even more if the Sbrick uses a feature (BLE) that is quite young in terms of adaptation.
But the SW is a mess or better say the disparity compared to the 'equality' as presented in the KS campaign. There is no priority announced for any of the platforms, even the need for 4.3+ android is not mentioned. So saying "iOS is a little better but at best is still beta" is a bitter understatement if one group can play with the working profiles (see that all the youtube videos returned for sbrick use only iOS profiles), another is left with mostly useless alpha test profiles (even missing the pledged ones) and last one (WM) cannot do anything now.
Although I would not use such strong words Steve, I understand the reason.
More so, if the SBrick team shown thorugh constant updates on the HW production, how even delays can be communicated and explained...
I mean, how hard would it be to hardcode to 'market' the profiles that iOS guys have since v3.0 from November to the Android app ?
Steve, I'm also a customer. A paying customer who also paid to be a beta tester. And a satisfied one.
I feel your pains, honestly. But SBrick is a crowdfunding product. Vengit went from almost zero to a full physical product in 4 months. It's a good product, there are already several people using it, you can find many videos here at social.sbrick.com or at youtube. And yes, the software component is very poor but it is alpha (Android at least, I thing iOS is a little better but at best is still beta). They are also releasing the protocol so it's just a matter of time until 3rd party apps show up (I've been using python and linux, raspberry pi, LEGO Mindstorms EV3 to control it almost from the first day I received my beta SBrick).
Could it be better? Yes, it could. And it will be. Just give it a few weeks more and give it some help and support.
Thanks for the help and the good idea!
About forum usability on android:
I can use it on stock browser, after blank page loaded, I click on "ask for desktop site" in the browser's menu. Then it reloads the page and after I can read/write. But it still very slow because of the f*** pile of JavaScript. :)