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Software / New robotics simulation and control software v2021
« Last post by HomeXYZ on December 30, 2020, 07:25:44 PM »
Here is a link to the new robotics simulation & control software version 2021:

Short video presentation: https://youtu.be/rpVpEJulcpA
Official website: https://www.babacad.com/Robotics
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Electronics / Re: 12v dc motor off and on continuously
« Last post by bdk6 on December 23, 2020, 05:36:53 AM »
There are several ways you can handle this.  The two ways you have mentioned, using a fan or a resistor in series with the motor, will both work but aren't necessarily best.  They both work by limiting the total current that can be drawn from the power supply.  But they limit it ALL the time instead of just on startup and they waste power when the motor is running.

Ideally what you want is to limit the current only during the time the motor is starting.  There are different ways to do that.  Perhaps the simplest is to use an "inrush limiting thermistor."  A thermistor is a resistor that changes value depending on temperature.  This specific type is designed to lower resistance when it heats up so that the initial surge of current heats it up then it lowers resistance.  That is probably your best bet.  Google for "inrush limiting thermistor" and you'll get notes on how to use them as well as places to buy them.

But, no matter what method you use one of the first things you need to determine is how much current the motor actually needs when running.  You didn't mention what the motor is doing (what load it has) which is important.  The amount of current it uses depends partly on the load.  The motor may have a data plate that says, or you may be able to find specs online.  Or, if you have a multimeter that measures about 10 amps you can just measure the current.  You will need that information to determine ANY type of current limiting unless you just want to continue "cut and try" which I don't recommend.

A few notes on what you've done so far.  The fan you used has a max current draw (usually listed on the fan) that applies when it gets its full 12V.  Your fan + motor circuit can NEVER draw more current than that. (That's not quite true.  The fan is a motor with its own inrush current.  But it's likely smaller.)   It is likely much lower than the max of the motor.  In addition, the voltage then divides between the fan and the motor.  You can measure that while its running.  Let's say they divide evently, each getting six volts.  Now your motor is running on 6V instead of 12.  It is likely the motor is getting somewhat less than six.  The resistor does the same thing but without an inrush current for the resistor. 

If you want to use a plain resistor, a little Ohm's Law goes a long way.  If you aren't familiar with Ohm's Law you should look it up.  It is a foundation of electronics.  Here is a brief overview:
I = V/R        Current through a resistor (I) is Voltage (V) divided by the Resistance (R)
R = V/I         Rearranged to find the resistance from the known voltage and current
V = I * R       Rearranged again to find voltage from current and resistance
So let's say you want to limit the inrush current to 3 amps with a resistor.  Use 12V and 3 A to get 12/3 = 4 Ohms.  A four ohm resistor in series with the motor will make sure the circuit never draws more current than the  power supply can handle.  Resistors also have a power rating: how much power they can turn itno heat without damage.  Common values for small resistors on circuit boards are 1/10 Watt, 1/8 Watt, or 1/4 Watt.  You will most likely need one much larger.  The full load on startup will be 3 amps and 12 V.  Power is volts times amps.  So that means 36 Watts.  However, once it starts running the motor will take some voltage and limit the current even more.  The resistor can take an overload for a short time while the motor starts.  But you need to know what the steady power rating needs to be.   Again, you need to find out how much current the motor draws.

This has been a lot of information and most likely confusing.  If you have any questions, just ask.
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Electronics / 12v dc motor off and on continuously
« Last post by DanieSpreeth on December 22, 2020, 01:37:23 AM »
Hey Guys!

Hope someone can assist me here... I have a 12V DC motor that works fine when connected to a battery source, but when connecting it to a 12V 3A wall adapter, it starts and stops repeatedly.

After a lot a searching online I did figure out its because the "draw current" when starting is too high when starting the motor causing the power supply to cut out. To confirm this I also added another 12v fan in series which causes the motor to work, but of course the 12V is now being split to the motor and fan (also just a motor really) and I both dont want to run both all the time and think it might not be good to run 2 x 12v motors in series with a 12v psu - but I might be wrong - if it is safe and Im happy with the reduced speed can I run it like that?

I also seen it mighty be possible to add one or more resistors (in series) which might also fix the issue, but I have no idea which resistor to use nor how many (Im an out-of-work software developer learning electronics). Should this be the best fix, how do select the right resistors? I have tried a few already but to no avail - I suspect they might not provide enough resistance (could be too much as well - again I have no idea).

Without purchasing an expensive new PSU that can handle the current, is there another solution that someone can possible explain to me please?

Thanks in advance for the help!
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Software / LifeAI artificial intelligence system
« Last post by jeremiahg on December 15, 2020, 02:24:58 AM »
LifeAI is an artificial intelligence system that simulates key processes of our minds, such as organizing data into concepts and categories, planning actions based on their predicted outcome, and communication.

  • Open source, C++
  • Object detection and recognition
  • Concept forming with properties and visuals
  • Categorization of concepts based on their similarities
  • Action planning that factors in prediction and utility
  • A messaging system that allows data to be entered and retrieved through natural conversation

Here is a recent demonstration I made of LifeAI applied to a robot named Cozmo
 https://youtu.be/K_C48_MlvBU

Visit http://www.lifeai.com for more information.
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Mechanics and Construction / Re: Robot horse neck
« Last post by bdk6 on December 09, 2020, 07:27:22 PM »
I can't fully answer your questions, but maybe offer some tips and advice.  First off, NEMA 17 doesn't mean much except the size of the mount.  https://kurz.com/wp-content/uploads/2019/03/LEESON-Frame-Sizes.pdf
Within any mount size the electrical and mechanical aspects (power, speed, torque) can vary a lot.  So specifying NEMA 17 tells you pretty much nothing about its capabilities.  Second, if you don't need precise positioning, which I suspect you don't, I would recommend some kind of linkage instead of direct drive.  Cables of some sort would be great.  You can put the motors wherever works best and put loads on the motor bearings the way they were intended.  Third, springs would work but I think a counterbalancing weight would be better.  You can set it up in whatever way works best.  For instance, you can make it so the head is pretty well balanced or you can set it up so the counterweight pulls the head up until the motor pulls it down.  That way gravity is helping you in most cases.  Most steppers don't provide a lot of torque.  Cables can be attached in whatever position gives you the best strength vs speed compromise -- assuming the steppers have enough torque to move it at all.  The circuit you use to drive the steppers as well as the type of steppers you use will have influence on the torque and power available.
Hope this hekps
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You are 100% correct and I love the RD->DC tutorial in the link you posted.  Well done! 
In my many hours of research I found a prefab TReX Jr which seems to do the same thing. 
Thank you again.
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The picture you uploaded appears to be corrupt and I can't open it, but I'll attempt to do some guesswork without it.

From what I am guessing, is that your receiver is outputting signals for a servo, but you are trying to hook up a dc motor to it instead.  This isn't going to work for what you are trying.  To make it work, you need something to convert your servo signal into something appropriate for a DC motor.  Example Here (there are several things you can do to accomplish this.)

If I'm wrong in my guess, let us know: 
  • What kind of motor are you trying to hook up?
  • What (if any) circuitry you are using between the receiver and the motor.
  • What you want the motor to do (Stop/Start?  Start and move proportionally up to full speed?  Reverse to Forward and all speed in between?  Act like a servo?
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Mechanics and Construction / Robot horse neck
« Last post by SvdSinner on December 07, 2020, 12:44:56 PM »
My 14yo daughter and I are building a robot horse.  I'm working on the mechanism to allow the neck to raise, lower, and move side to side.  My idea is to use 3 linear actuators in a triangle to create the motion.  the ends of the actuators will be free to swivel.  I am constraining the lower actuators to not point down (from the torso) and the upper actuator from not pointing up.   See the attached image of my first iteration of the mechanism.  (I'm new and couldn't figure out how to display the attached image inline)

Upon completing this first drawing, I worry that the weight of the neck might damage the stepper motors or the threaded rods due to high radial and axial loading.  (The neck and head frame weigh 3.9lbs bare and the head will eventually add 5-7 servos and a speaker, and it will eventually be covered in "fur".  The torque of just the frame is currently 3.3ft/lbs.  The center of the head and the weight of its future mechanisms is about 18" from the base of the neck, which adds an additional 3ft/lbs torque.  That means a static axial load of 8ish pounds on the top threaded rod and 4ish pounds on the bottom two.  Dynamic forces as the horse moves will be much higher.)  I am trying to figure out how to better support the weight of the front without hurting the steppers or the threaded rod.  I'd like the joint to be strong enough to prevent it from breaking the first time a child tries to pull down on the head.

Some ideas I've thought of (but am not fully sure of their value): 
  • I can move the mounts on the torso further towards the top and bottom (while keeping the mounts on the neck in the same position) to trade off some radial load for more axial load.
  • I can add a 608 bearing to the lead screws (mocked up on the bottom two steppers) to increase support.
  • I could/ "hang" the neck with some tension springs to off-set the weight of the head/neck.  I don't have much experience making custom springs, but I realize they would need to have a certain tension so that they don't make the axial forces worse.


1)  Does anyone know the rough limitations of Nema 17 steppers as far as axial/radial load? 
2)  How much radial would 608 bearing to be able to handle?  (It obviously isn't a thrust bearing, but is designed for some axial forces.)  For cost reasons, I'd rather use 1 (or more) cheap 608 bearings than dedicated thrust bearings, if possible.
3)  Any suggestions on how best to bear the weight and torque of the neck/head in a mechanism like this? 
4)  Any major flaws of this mechanism that I'm not seeing?
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Software / Re: Anyone tried Windows 7 for robots?
« Last post by elwishtwo on November 25, 2020, 11:21:28 AM »
I have downloaded the community edition but unable to install it. Itís asking for the .net framework. I tried installing the .net framework 4.5 / 4.6. None of them are getting installed on my system which is windows 7 . Have Installed SP1 as well. Could you please support me about what is to be done next.
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Electronics / Re: charging two diffrent types batteries with one charger
« Last post by bdk6 on November 24, 2020, 06:16:00 AM »
Every type of battery has different charging requirements.  Lead Acid and LiPo are VERY different.  Each should have a charger especially designed for it.
You don't state what type of "charger" you are using.  I have a feeling it isn't intended for either type of battery.
LiPo batteries are subject to catch fire or even explode if charged improperly.  Lead acid is less dangerous but can still be damaged or destroyed.
I HIGHLY recommend you buy appropriate chargers designed for each type and use ONLY those.

There is a great deal of information on batteries and charging here: https://batteryuniversity.com/
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