Wednesday, February 27, 2008

B9 Electronics: The Inside Story Part 1 - Tread Section

The electronics of a B9 can be as simple or as complicated as you want to make it. To assist me I visitied (several times) to boost my electronic knowledge and skills. There are a lot of sites like this one but I wouldnt let my fear or lack of knowledge hinder me in getting my robot to do what I want him to do. After all, WHO is the master here? Me or him??
Well, anyway, to facilitate this blog discussion I will be going over various systems in am or will be using in my robot. Because this is usually a touchy and potentially complicated subject I will be dividing it up into several parts. As a single point of reference the RC transmitter and receiver I am using is the Spektrum Dx7 with the AR7000 receiver with fail safes set (at binding) to zero forward velocity, forward hip set to "slump" and contact closure set to announce "Warning, Warning, remote control connection lost".
What makes a B9 go? Money....I mean Motors. BIG Motors! See the heading called "New Drive Section" below. Two (2) NPC Br81 and Br82 24v wheel chair motors with Two (2) 6" 65 durometer rubber wheels for traction and shock absorption. Two (2) Gel Cell 12v 33ah ("Marine" or "Deep Cycle") batteries, plenty of 10 gauge stranded wire and a Vantec motor controller RDFR23 along with a 24v DC power supply (yes, you can plug him in and drive him around with a really long extension cord if you had to).
I started by wiring the two (2) 12v batteries in series to achieve 24v. You do that by taking the positive of 1 battery and connect it to the negative pole of the OTHER battery. Once that was done, you attach wires to the unused poles of the 2 batteries and connect them to a central, resettable fuse block and distribution panel in the left tread section. [I originally had this area in the hip section but then realized how much of a PIA it would be just to reset a blown fuse (pulling the torso off and resetting the fuse would require at least 2 people probably 3, etc)].
The Vantec controller connects to the RC receiver with 2 servo like connections; 1 marked with a "T" for throttle and another with a "S" for steering. Plug those into the corresponding slots on the receiver and you are ready to learn how to drive your "bucket of bolts". [As a side note make sure you do not adjust your power curve for forward or reverse throttle. Try it out at its default setting first. You don't want your "bubble headed booby" popping wheelies or doing somersaults!] The website for the Vantec Manual is this: Take a look at that as it gives you detailed information on how to setup your controller for proper operation. I will also wire in and use one of the switches in the programing bay to turn off the motors for safety reasons and to concerse battery power.
Because the soil sampler will be in the right tread section, you want to take into account that a power feed will need to go to that tread section. Do not forget to put a fuse in line for the soil sampler. Also, the soil sampler is powered by a 12v 3 rpm motor. Since my power system is 24v I have to either draw off of 1 12v battery (which isn't recommended because it will cause an uneven drain on your primary batteries) or have some load balancer in place. The other obvious option would be to have a separate 12v battery that could be used for the bulb lights, neon and sound amplifier. I will option for a separate 12v 12ah battery. This should give me a full days capacity at shows and special events (I am only looking for 8 hrs of use). There was another consideration. I could change the motor of the soil sampler to a 24v geared Tsukasa electronics company motor. I seriously thought of that but then considered the issues with the lights in the torso and a further breakdown from 12v to various other voltages. I found a power distribution board that starts with a 12v source. It breaks down voltages for your RC receiver and other components like the 3.3v for the teeth lights, 6 volts for the belly, finger and brain lights and 5 volts for the RC receiver. Therefore I opted to stay with a separate 12v battery that I will keep in the CSS by one of the vents (so I can R&R quickly or just charge it easily).

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