Let's Make Robots!

How many 9g servos can an USB handle.

I need some confirmation to be sure - USB 2.0 can supply 500mA, and typical small 9g servos draw like 150mA, right? That means it's safe to have an arduino powering 3x 9g servos, running off an USB port..?
Also, how important is it to have an electrolytic capacitor in the start of power supply chain, to store current? At least in this particular case - how much will it help protect the USB port? Or if all motors are stalled, capacitor will run out of stored power, and the USB port can still be damaged?

BEAM Robotics

I am building a three wheeled, light sensing BEAM robot as part of an engineering project, but my knowledge on electronics is very poor. I was wondering if someone could help me with the circuit. My robot is going to be light sensing with a touch sensor around its perimeter so that it can avoid obstacles.

Trouble Collecting


First day joining LMR. Love this site! I found a number of robots that I would like to follow the progress on. But when I click on the Collect link I get a HTTP error 200... I am using Google Chrome has anyone had this before?

Really sorry if this is this wrong spot for posting this, I did a search and came up empty...

ganging servos together

I am in the design phase of building a robot arm roughly 40 cm long that can pick up several pounds ( 1 kg for easy math).  To get a 40 kg-cm torque servo is a pretty expensive servo ($60 at pololu.com although anywhere else anyone knows something cheaper, please share!). 

Has anyone ever tried to gang several servos of the same brand and type together to work in concert?  I was going to put a balancing weight on the far end which will help, but still calls for a pretty expensive servo (30 kg-cm)

How to calculate how much weight my servo can handle?

I have a Tower Pro 9g Micro Servo (SG90) and it's datasheet says it's stall torque is (Stall Torque at 4.8 volts = 16.7 oz/in (1.2 kg/cm)), but as I haven't learned physics, I don't know how to calculate how much weight it can handle stacked on top of the arm/horn.

Can't upload any pictures

Hi there,

I can't upload any pictures for some reason. This is what I see when  I open the upload window:

Directory error! - files/userpics/u21387

Anybody an idea?

I'm trying to put up a write-up about my BoBtheBiped...



Can you make a logo for LMR 3D Print Club?

A 3D print Club needs a logo. and yes, of course it needs to be downloadable, so it can be printed out ;)

There is no prize other than fame and glory - but it would be a great help if you could make a nice and cool 3D printable logo, and link to it / share it in the comments below.

Thank you very much :)

More info about LMR 3D Print Club ->

Damage Assessment on the Kossel

Well, I ran into my first real fail of cheap parts.  Apparently the RAMPS 1.4 board I bought has two defective mosfets.  I'd like to take the blame and say I blew them, but I was being insanely careful.

And after inspecting the mosfets I've found physical damage to them.  Sigh.

Do we want a LMR WhatsApp or WeChat group?

A while back I asked Frits what he would think about a WhatsApp or a WeChat group for LMR. 

Recent events about WhatsApp may change a lot but I guess that's a reasonable question if we want a 24/7 chat for LMR or not. The SB is ok for the use on a computer and the SB app is doing it's job as well but it's still not an optimal solution.

What I would like to read below is your opinion about that idea. Do we need a group and if yes, how we are going to do that?