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Sbrick and 5292 RC-Motor

    • 99 posts
    November 12, 2015 9:23 PM CET
    • 99 posts
    November 12, 2015 8:09 AM CET

    Coming soon...

    I have measured, with several cameras, the real speed of two test chassis equipped with two RC Buggy motors:

    - One based on the Lego RC Unit

    - One based on the SBrick

    Video and results will be posted soon :)


    This post was edited by Marc Jaouen at November 12, 2015 4:10 PM CET
    • 99 posts
    September 5, 2015 10:26 AM CEST

    An illustration of the concept in this quick-made video:

    https://social.sbrick.com/videos/9334/219

    • 87 posts
    September 2, 2015 2:55 AM CEST

    Sorry, did not understand you had already modded the PF battery.

    Old 9V-type cable isolation is very poor, new PF cable isolation is somewhat better... but when using a few Amps even the PF metal contacts tend to get to hot, so if you don't burn the cable isolation you melt the plug.

    If you really want more power, consider using RC car/plane batteries. I used a 2S 7.4V LiCoO2 1500 mAh battery for my early SBrick stress tests, costs 1/4 of a LEGO LiPo and lasts 2x more (but you also need a charger). It has 25C capacity so in theory you can get 37.5 A (play safe, please).

    • 99 posts
    September 2, 2015 12:30 AM CEST

    Jorge, I have bypassed the current limiters a while ago: that's why I can use the 5292 with a correct power, and that's why I can use 2 motors at the same time with one BB only ;)

    I have kept a standard BB of each type with their limiters, and have modded one of each (large modele and small model).

    As for the cords, you're right : during my attempt the other evening, the plastic isolation of one of my old 5306bc015 cords was like cooked and was falling apart !!!! I'm going to replace that by loudspeaker cord (you know, the type used in cars stereo) or something similar: I have tons of wires and components at home, but of course, it was the cord I needed that was missing !!!

    What I don't like about LiPo batteries, apart from their cost (60€ in France), is their lower voltage compared to standard batteries: you lose 18% voltage just to save 30g, it's not that interesting.

    What I don't like about standard batteries is that they don't last long: after 10 or 15 minutes, you clearly feel the power diminishing !

    • 87 posts
    August 30, 2015 12:06 AM CEST

    Sorry for you disappointment but that behavior is expected when using Power Function batteries because they have internal protection to cut at ~800 mA, much less than what a single RC motor can consume.

    You could disable the internal protection (search in Eurobricks forum) or make your own PF battery with something like a RC 2S LiPo and half of a PF cable. Be carefull, wire diameter of PF cables cannot hold much more than 2A, could melt with 2 LEGO RC motors at full power.

    But I like your relay idea, gave me some ideas for the future :)

    • 99 posts
    August 29, 2015 11:25 PM CEST

    Before I can publish the corresponding video, the result is both disappointing and very interesting...

    No speed record. As a matter of fact, the 2 RC Buggy motors directly connected to the plain DC of the Battery Box do not run better than with one SBrick using PWM control.

    The interesting point is that a single SBrick can drive 2 motors with a maximal efficiency. Using 2 Sbricks for 2 motors does not, in a first approach, provide more power: if one can build a faster car, it's because of the mechanical design, not because of the electric power management.

    I must now complete this benchmark with a car built with the Lego RC Unit, but based on what I've measured tonight, there's no reason why the speed should be higher.

    • 99 posts
    August 28, 2015 10:34 PM CEST

    Hope I will break another record this week-end : I have built a relay with an M motor activating a 8869 control switch. I can thus send the plain 9V DC current of the battery box to a pair of 5292 motors, instead of the PWM signal.

    It's a binary control: 0V or 9V, that can't even set the car in rear mode, but by experience, the only interesting mode for a fast car is full forward speed :)

    • 99 posts
    July 27, 2015 10:14 PM CEST

    I have reached 14,8km/h with a test chassis : https://social.sbrick.com/albums/view/259

    The interesting point is that one Sbrick can drive 2 RC Buggy motors. Yet:

    - with the same small wheels (41896 wheels with 41897 tyres) as my Ferrari, the speed was the same: 10km/h. I have used here the larger 44772 wheels fit with 44771 ZR tyres.

    - this speed was possible only because of the very light chassis (623g without the phone, 820g with the smartphone used to measure the speed).

    When you see what RM8 has done with 2 SBricks and his amazing Baja Truck (https://www.youtube.com/watch?v=4vaaO1WTCio), it is clear that the global output power of the SBrick is the limit: it cannot drive the 2 motors at full power.

    I plan to add a MOS-FET H Bridge, its the classic way to add power to a low-current PWM source. Shouldn't cost much, and will be easy to house in a small lego box...

     

    Edit : the proof that you need one Sbrick per RC BUggy motor to get the full power out of them:

    https://www.youtube.com/watch?v=w7vHOpuCZ9w

    24km/h !!!!!

    Guess why my wife considers she's the only adult in this home - lol !


    This post was edited by Marc Jaouen at July 30, 2015 5:56 PM CEST
    • 99 posts
    July 14, 2015 11:56 PM CEST

    I have 2 RC Buggy motors now and have tested 1 SBrick driving these 2 motors (one per port). Assigning the same acceleration to 2 different ports (or 3, or 4) is straightforward and it works perfectly. I must now build a test chassis to test that in real conditions :)

    As for battery boxes, a few thoughts:

    - The current trend is to use LiPo batteries, but they deliver 7.4V only while standard non rechargeable batteries deliver 9V. Saving 30g on one hand while losing 20% power is not that interesting... I use standard Duracell batteries and that works fine. I get a better power over weight ratio, and it doesn't cost that much when you know the price of the 8878 (60€ in France, plus 30€ for the wallwart).

    - I have bypassed the current limiter of one of my 88000 BB's, that's what I use for cars with one 5292 motor.

    - The large 8881 has also a current limiter but I didn't experience any cutdown issues with my first test chassis (http://www.mocpages.com/moc.php/410964) that had one 5292 motor.

    - I have a red-switch battery box (I bought one for a few euros a while ago). it's a  semi-rare item that was sold in 2006 in two sets : a large helicopter (4895) and... the 8287 "Motor Box" that contained a 5292 motor plus a bunch of technic parts. The current limiter may have a higher limit and may handle 2 motors - to be tested.


    This post was edited by Marc Jaouen at July 14, 2015 11:57 PM CEST
    • 167 posts
    May 7, 2015 4:44 PM CEST

    Paralleling LEGO LiPos could be a bad idea. Different speed setting on their dial is esentially will cause a short circuit (for a brief moment 1000 times a second). Also, parallelling  differently charged LiPos can result in very high currents. I don't know exactly how well LEGO lipos are protected against shorts, but I've managed to kill two battery packs by momentarily shorting the power leads.

    However if you can manage it safely or replace the LEGO batteries with a DIY solution, you very well can drive two RC motors with a single SBrick. There's one MOC sitting in the office window right now, and it uses an unprotected LiPo battery (1P2S, Turingy, 1500mAh If I remember correctly).

    SBrick can easily deal with the high (~2-3A) surge current the RCs are drawing on start, and once running they don't draw that much current at all if the model runs on a smooth surface, and there are not too many gears (too much friction) between the wheels and the motors. I suggest connecting the RCs directly to the wheels with a rigid axle, and using a thin silicon lubricant where friction is present. Our modely is almost too much fun to play with :D

    • 2 posts
    May 3, 2015 3:23 PM CEST

    Is it safe for one Sbrick to have 2 Lego lipos attached to the power input and 2 RC motors on 2 different ports?

  • February 20, 2015 11:21 PM CET

    Thanks guys, specially for reminding me of overheating issues. I'm hoping to get 600 mAh batteries in a few months, but for now I'll just stay with small scale models (1 motor) or figure out how to use 2 channels (1 per motor). I'm stuck with Android anyway (no iOS device) so I also have to wait for the app to get a bit better, it's still quite tricky to get it to work... but I can wait, I'm having my 2nd baby any day now :D

    • 198 posts
    February 20, 2015 1:14 AM CET

    You can assign the same control for muliple ports on one (or more) sbrick in the app. It's a little help when you plan to use muliple power source in your creations. :)

    • 87 posts
    February 20, 2015 1:00 AM CET

    2x 9V Motors? That's probably more than 3A, the SBrick cuts power at 3A (per port) that's why you see "just a few miliseconds and stop" (also amazing you get 3A with just PP3-style batteries... a 250 mAh will last less than 5 minutes at 3A but watch its temperature... it might explode).

    You'll have to wait for multi-port support.

    Until that happens you can try reducing power consumption to just 2.8~2.9A. You can do that applying 6~7 Volt instead of 8~9 like you're doing now - adding something like a power diode or resistor in serial with the motors or using a 4 AA battery pack with a PP3 plug to connect to your MiniZip.

    But if you're using 2 RC motors in one port I think you don't want to reduce power at all :)

  • February 19, 2015 11:58 PM CET

    Yes! And while you're at it, why not create a modern replacement for the 5292 motor? Seriously :)

    But for now, I'm using 2 MiniZip with 9V NiMh batteries, 1x 200 mAh and 1x 250 mAh. Not the best worldwide, but the best I could get locally at a reasonable price.

    1x 5292 motor works well, but it seems like 2 motors on 1 channel makes something freak out and motors won't even start, or maybe just try for a few milliseconds and stop.

    I'm OK with dedicating 1 channel per motor, but can you please make it easy (in the Profile Designer) to assign multiple channels to 1 control?

    I'd like to use the joystick and have "acceleration" use channels B & D together -- then channel A for steering and C for something else, e.g. PF lights.

    Or, if I can make this work with both motors in 1 channel, please let me know how.

    Thanks!

    • 87 posts
    February 10, 2015 4:53 PM CET

    [blockquote]Lénárd Pásztor said:

    We also thinking about creating a battery that designed to use with SBrick.

    [/blockquote]

    Oh boy, that would be great! Something like the Power Functions LiPo battery with built-in charging circuit and a plug to connect a common wall adapter power supply (like the PF) but with a 5~6A limitation instead of just 800 mA.

    And several sizes, like S (just 500 mAh to be used withou cable, just plugable to the bottom of the SBrick, with the same horizontal dimensions of the Sbrick) and L (say 5000 mAh)

    I buy it, tired of cutting and soldering LiPo cables and power Function cables.

    • 198 posts
    February 10, 2015 4:36 PM CET

    I think the best way is to replace the LEGO battery to a custom one. LEGO batteries limiting the outputs by design.

    We also thinking about creating a battery that designed to use with SBrick.

    • 33 posts
    February 10, 2015 4:25 PM CET

    Hi,

    i just wonder, what options we can have to "speed up" the 9398 crawler truck (the orange-black masic model). It would be more spectacular if it could travel faster, while keeping the climbing capabilities or torque at least as good as it is today.

    Do I have to install stronger motors? If yes, would SBrick provide enough current for them?

    Or, do I have to replace the battery unit only with a more powerful one? How Sbrick would behave then?

    Any guidance is much appreciated!

     

    Peter

     

    • 87 posts
    February 2, 2015 3:50 PM CET

    If you're not familliar with this kind of hacking or if you want to stick with LEGO only (besides the SBrick, of course)  you can use several LEGO Power Function Batteries in parallel like here:

    https://www.youtube.com/watch?v=lba1u_IQIK0

    8each LEGO Power Functions battery - LiPo or AA or AAA) has protection that limits maximum current to 800 mA. With 2 in parallel you can have 1600 mA, 3 = 2400 mA...

    • 198 posts
    February 2, 2015 12:46 PM CET

    Hi Michael,

     

    Yes, you can use the RC motor with SBrick. Once the SBrick package has not contani extension wire, you need to buy it at the LEGO(R) store if you don't have one.

    About the power sources.. The LEGO power sources contains limits on current, so if you want the maximum performance you shoud connect your SBrick with a custom LiPO battery.

    • 2 posts
    February 2, 2015 12:06 PM CET

    Hi,

     

    I'm all new into power functions and RCing Lego sets. I would like to go all Sbrick and dont bother with the classic PF infrared control at all.

    Before I buy an sbrick, I wanted to know if I can control the speed of an 5292 RC-Motor with the Sbrick (thus having a better control than a simple a full-on/full-off control of this motor).

    I watched the vidio of the Super car with the sbrick, it appears that slow speeds are possible, I just want to be sure.

    Are there other issues I would need to address? Cables, power supply?

    Thanks in advance,

    Micha

     


    This post was edited by Michael Koehler at February 2, 2015 12:06 PM CET