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Electronics / Re: decoupling capacitors for encoder
« Last post by mstacho on Today at 09:38:29 AM »
Good suggestions.  A cap between the two lines (and another try with a cap to ground) helped, but it turns out that the problem wasn't the interrupts at all.  The circuit was connected to motors and the motors were giving HUGE voltage spikes into the arduino (hence why the caps helped, I assume that the encoder signals weren't the issue).  However, curiously, once the motor was put onto another circuit (but was still in close proximity to everything else), the spikes remained.  Could this be RF interference or is it more likely to be a wayward wire shorting something out?

With permanent magnet DC motors at a high duty cycle (or constant on), if the motor is turning slowly the current is much higher than when they are turning fast. So, if you load up the motor and force them to turn slowly many will overheat and potentially burn out due to the excess current.

It sounds like this is what is happening with your system - the motors do not have enough torque to get your device moving fast enough to allow the motors to spin at their rated speed. You can change your gear ratio to allow the motors to spin faster or you can get more powerful motors.
Misc / Motoman Robots - Just In
« Last post by PTD on Today at 07:34:22 AM »
HGR Industrial Surplus currently has 9 Motoman Robots and/or Robot Accessories in stock. You may follow this link for any additional information: http://bit.ly/1toWtK2

To view all robots that we currently have in stock you may follow this link: http://bit.ly/1yM2KRy
Change in plans -- after reworking the motor selection process, and gaining a greater appreciation of my lack of knowledge, the J-Bot ver. 1.0 will use Pololu 6V motors product # 2275 and Pololu motor driver product # 1451with the following specs:

motors: 6V 130RPM @ 450mA Free Run with 130 oz-in 6A stall

motor driver: 5.5-24V, continuous current 12A (peak 30A), 2.5-5V logic levels (will work with Pi) PWM up to 20kHz

My circuit building activities will be limited to a GPIO breakout board for the Pi that is fitted with both opto-coupling and level shifters for output and voltage dividers for input.

At this point I finally feel comfortable enough with my plan to proceed with construction/assembly.



OK, not sure if this is best place to ask but figure best place to start. I built a RC Lawnmower. The electrical is very simple. I used the Sabertooth 2x25A Motor driver by Dimension Engineering. I am also using MY1016 "scooter" motors. Ratings are 24V 280W 15.5A @ 2750RPM. There is a 30A Automotive Switch on + to the driver board to kill circuit. I used 12V battery source at first (one car battery) and it did oooooK I guess but was slow and no power. I put car battery 2 in series and it made difference but still week. Also, motors got so hot they were blowing smoke... Gear ratio is 1:5 right now. Maybe I'm wrong, but two of these motors should have some umph behind it, but I get stuck in a rut... and using 24V they're smoking after about 15 min of use. Help? This thing is gear the same as the scooter 5:1. Just frustrated as all this time and money put in this and now I'm stumped.

Here is link to album of my mower if anyone is curious and wants to see what I'm working with.

Electronics / Re: decoupling capacitors for encoder
« Last post by waltr on Yesterday at 12:48:49 PM »
If the encoder signals have noise then the cap would help buut a cap on each line to it common (ground?) line would typically be better.
How long are the lines to the encoders?
Are they in a noisy environment (attached to motors)?

Are you running the Atmega's UART for serial or using 'soft serial"?
I would use the UART and write interrupt driven UART routines so that the processor runs as little code as possible for serial.
Electronics / decoupling capacitors for encoder
« Last post by mstacho on Yesterday at 11:58:33 AM »
Hi all,

I'm working on an encoder-to-arduino interface.  I have arduino Unos, which means that its two interrupt pins are right next to each other.  I am using a quadrature encoder with 200 counts per revolution, rotating at around 200 rpm.  This is apparently *really* fast for an arduino (40K interrupts per second) especially when also using serial.  My arduino tends to crap out (it freezes and serial is not longer sent), and this problem occurs arbitrarily (it may happen in one second of turning it on, it may take a full minute). 

I've soldered a decoupling cap. between the two interrupt pins and this *appears* to fix the problem, but I'm not sure if the problem actually got fixed or if I just magically happened to get it to work for a few days and it will fail again.  Does it make any sense at all that a capacitor between two digital pins that are beside each other and toggling rapidly would help?  Would that setup (without the cap) be a recipe for killing the circuit, or could it be something else?

Misc / [ForSale] RoboWorx.com - Premium Robotics Domain For Sale
« Last post by bjsvwx on Yesterday at 11:45:49 AM »

- Premium Robotics Domain For Sale
- One off opportunity
- Please make any serious offers by PM
- Once sale is finalized, transaction through Escrow.com
- Robots.com, RobotWorx.com are already developed domains with big companies
Electronics / AC battery recharging system without disconnecting
« Last post by ramblebot on October 29, 2014, 05:04:25 PM »
Ive been scratching my head on this for awhile. So I have an arduino telepresence bot project and I need to come up with a method of remotely recharging the batteries without someone manually doing it. I was thinking of a roomba style AC contact point but I need some advice on the best way to go.
The format is an rover 5 chassis with an arduino uno r3 + L293D Motor Shield , at first i tried 6x 1.2v NiMH 2400mah AA's but the voltage didnt seem high enough for the motors (Motor rated voltage: 7.2V) which seemed sluggish so I added another 2 AA's and it seems to be fine voltage wise. All up 8 AA's now.

So I need to remotely recharge these, being telepresence i cant manually open up the robot to pull the batteries out and recharge them every time so I wanted to come up with a relatively cheap way to recharge them via an AC point. The first bit of advice I got was that Lipos are no good for recharging while still pulling power to the arduino which needs to stay on through everything. I gather a charge controller circuit is required however most of the ones ive seen eg http://www.adafruit.com/products/259 are for sub 5v.   Id like 12-24hrs running time between recharges. If someone can suggest a good relatively cheap way to go id be very grateful.

I had a rough/cheap idea, I bought an 8 bay AA recharging bank like this http://www.ebay.com/itm/131218125319 and I was thinking of placing all the batteries within it and then running a wire from each + and negative to the +/- on the motorshield. The AC power cable goes to the contact station to recharge the batteries and the power should continue into the motor shield. I was planning to put a diode on each AA + wire to make sure they dont all connect up at the motorshield and trip the charger which seems to cut out when the batteries reach a certain voltage.

Apologies for my lack of basic battery / power knowledge.

Misc / [advertisement] New Gripper Kits!
« Last post by ServoCity on October 29, 2014, 01:23:54 PM »
Parallel Gripper Kit A - $14.99
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Standard Gripper Kit A - $9.99
Adding to our line of grippers, is the Horizontal Standard Gripper Kit A! This gripper is a sleek and simple kit that is great for all kinds of robotic applications. The grippers have a maximum width of 4.20 and contoured design to help hold on to larger objects. By incorporating the Actobotics 0.770 hub pattern into the back plate you can easily attach nearly any Actobotics component to the assembled kit. Designed for use with any standard size Hitec or Futaba servo (sold separately). The kit is easy to assemble and requires only a Phillips Head Screwdriver. Compatible with standard size Hitec or Futaba servos (sold separately).


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