Our Pet Robots

Guido Mifune

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Dear SERVO,

I built the photovore described in the BEAM article and the Nv neuron, but it didn't work correctly. It stayed on only when IN was connected to Vcc. I searched the Internet and quickly found that the capacitor in the neuron WASN'T POLARIZED, so I substituted a non-polar one and it worked perfectly — as described in the article. I'm not mad — just glad it works, but I would like to know what caused that error. It's still a cool circuit, though.

D. McGrath via Internet

Tom Gray and Wolfgang Goerlich respond:

Regarding the substitution of a non-polar one — which worked — there are a few things to keep in mind. In the Nv timer project, polarized caps should give good results. We've used tantalum caps and electrolytic caps — both of which are polarized — and they work fine. With a polarized capacitor, you have to pay attention to how it is placed in the circuit. For the Nv in that project, the capacitor's anode (+) goes to the PIC, and the cathode (-) goes to the bias point.

Regarding the statement, "it stayed on only when IN was connected to Vcc," — good observation! All Nv Neurons

Congratulations to Daryl Sandberg and Larry Geib for winning the 2004 SRS/SERVO Magazine Robo-Magellan Competition. Their autonomous robot navigated the farthest distance at Robothon's diminutive, DARPA Grand Challenge-inspired course.

perform that way. If you let go of the switch, the input is pulled low and the Nv shuts off. You have to hold the switch down (or something else to tie the input high) until the Nv times out. This effect is particularly noticeable with Nvs that have longer time-outs. Since polarized capacitors tend to have a higher capacitance than their non-polarized counterparts, you would most likely encounter this situation with a polarized cap.

.sauEiëfii

Our resident expert on all things

robotic is merely an Email away. [email protected]

Tap into the sum of all human knowledge and get your questions answered here! From software algorithms to material selection, Mr. Roboto strives to meet you where you are - and what more would you expect from a complex service droid?

.I have a power supply problem with my robot and I am hoping you can help me. I am using a BASIC Stamp 2 in my robot and it resets from time to know it is resetting because I have an LED that turns on for a second when the power is first turned on. I am using four Sharp GP2D12 infrared sensors with four LEDS to tell me which sensors are seeing the objects. The motors are modified Tower Hobbies TS53 servos. I am using a separate 6 V battery pack for the servos and a 9 V battery for the rest of the robot. I am using an LM2940 voltage regulator to power all the electronics. The regulator is supposed to be rated for 1 amp and, according to my calculations, the total current draw in my robot is around 280 mA — which is well below this rating — but my microcontroller resets from time to time. Some friends told me to put a big capacitor next to the voltage regulator, so I tried adding a 1,000 p,f capacitor to the voltage regulator, but that doesn't help. Do you have any other suggestions?

Figure 1. Solutions Cubed Easy RaÍÍer Matar and Encoder.

Figure 1. Solutions Cubed Easy RaÍÍer Matar and Encoder.

Pete Miles

^.First off, these Sharp sensors advertise an "average" current draw of about 35 ma, which can be very misleading. I have measured that these sensors have peak current draws of 200 ma when the infrared LEDs turn on and off. With four of these on your robot, they can be drawing up to 800 ma, which can really tax the ability of the voltage regulator to maintain the output voltage to the microcontroller.

I recently had this same problem with one of my sumo robots and found a very simple solution to this problem. Use two different voltage regulators: one regulator to power the BASIC Stamp and the other to supply power for the rest of the robot's electronics. In fact, all you have to do is use the onboard voltage regulator that is on the BASIC Stamp. By doing this, any momentary voltage drops from the sensors and support electronics will only affect those systems, themselves; they won't cause the BASIC Stamp to reset (assuming that the current draw is not high enough to drop the battery voltage below the dropout voltage of the regulator).

When I did this, I connected the Vin pin (not the Vdd pin) on the BASIC Stamp directly to the positive terminal on the 9 V battery and the voltage input pin of the voltage regulator was directly wired to the positive terminal of the 9 V battery. I did this so that the power sources branched out from the battery to minimize voltage drops from the different components in the system.

.My robot uses regular R/C car wheels and hubs mounted directly on the shafts of some gear motors got from Jameco. The problem I am having is that crews keep working themselves loose after a couple of days, no matter how tight I make them. Is there anything I can do to keep them in place — other than gluing them?

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