what do I need?
roughwire
Posts: 78
I'm about to·start a new project·in which I pretty much just want to a giant boe bot. I love my little bs2 and board of ed. I would love to make something like a giant one, because I like the compatable sensors and stuff. But the only thing is instead of small servos I would want to use some sort of big DC motors. Now am I correct in saying that I can't run much more power than a little 9V battery? I would want it so I could run a car batt. through it and use the sensors the same, and instead of servos, they'll be motors. Is it possible or should I get some differnt kind of curcuit board?
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MIKE
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MIKE
Comments
Although most Stamp development boards will run off a 12V supply, it's much better to have a separate regulator that runs off the 12-14V battery and produces 8V, then use this for all of the logic boards that have their own +5V regulators. It helps isolate the logic from the noise from the motors that gets on the battery circuit and it reduces the heat that the logic board regulators have to get rid of. You could easily use an LM7808 which is cheap and rugged and could supply 1A at 8V. You should have filtering (a choke and capacitor) ahead of the LM7808. Radio Shack sells chokes for use in automobiles for noise suppression. The choke would be between the regulator and the battery circuit. The capacitor should be a 0.33uF ceramic and at least a 100uF electrolytic rated at 35V in parallel close to the regulator input terminals. The output should have a 0.1uF ceramic capacitor across it close to the regulator and the regulator will need a heat sink which you could also get from Radio Shack if you want.
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MIKE
Vern
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Another option might be a big NiMH battery pack. They are much more finicky about how they are recharged though, lead-acid batteries are comparatively simple to recharge.
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- Rick
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You can get some· "F" size nicad's they are a little bit longer than a "D" size
Battery· They start at 7 amp hr i think i have seem them at up to 14 amp hr
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Here is one link................http://www.bbmbattery.com/NiCad.htm
I only posted the battery sizes for not the prices
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There are more than one place that· you buy these batterys
When do a web search F size nicads
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·I have used these battery before and they are very good battery
The one's from Sanyo they are from Japan
The one from China do not tend to be good battery they dont last long
I have not order for them before
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If this help you out let me know and i will look for them agian
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··Thanks for any·
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Sam
Post Edited (sam_sam_sam) : 4/13/2007 9:25:07 PM GMT
Motor size: don't underestimate the power of a gear head motor. My first large robot I used windshield wiper motors they were so powerful I could sit on the bot and it would still move. The power consumption was so high I drained my larger battery with in an hour. find a nice gear head motor, and keep in mind that if you gear it down further you'll gain even more torque. on my 2nd bot I used motors about 1/2 the size of the first and they are still over kill but the price was right. My motors draw just over 4 amps with load which I have found pushes it into a different price range for motor drivers. If you can find some that are 2-3 amp max your motor driver will cost much less I'm currently using relays to control the motors but that's just a temporary fix. keep in mind most sites list no load amperage. and with DC motors the amperage goes up with torque.
Battery size: I bought a Marine Battery (think car battery that can handle being drained multiple times) from a local battery store it measures 7"x5"x6" it's a really good battery but I had it sized for the first motors and it's over kill for my current project. The cost was $89.00
Wheels: I use lawnmower wheels from Home Depot. They are fairly cheap and are easily connected. They have 4", 6" and 8". Remember to factor in wheel diameter when calculating desired speed. for the front wheel I used a caster. I originally used a 2" caster wheel. I had to block it down quite far which made it unstable and because of poor weight distribution the caster wouldn't roll over objects very well. I changed to a 4" caster and had much better luck with it.
Chassis: I built the chassis for my first bot about 8 years ago and decided it was time to use it. I made it out of 1" flat steel. and welded a box frame. it was way over kill my son enjoyed sitting on this bot as it drove around, this bot was a tank. Home Depot sells flat steel and aluminum that can be bolted or welded. I have found plastic to be a really good medium to work with, light weight and cheap. I use 3/8" sheets to do most of what I make. I connect tiers of it by threaded rod.
Sensors: I used some welding wire to make some bump sensors I don't actually have them connected yet so I can't tell you how well they'll work. I have a Ping ultra sonic range finder mounted on a servo. and also have IRPD sensors. Google TTT IRPd. it's a good source for the IRPD. Inexpensive also.
Because my battery weighed a ton, placement was critical to the bots performance when driving and turning. I originally had it too far forward and it would lose traction easily, and as mentioned above wouldn't go over the smallest bumps. Carpet was not an option until I went with a larger caster because the 2" caster would dig too far into the carpet. place most of the weight over the main drive axle.
This is a pricey venture. I didn't quite know what I was getting into when I started. my current project is about 40% complete and I'm into it well over $200.00 I'd make sure you have the funds and warn the wife as to avoid unwanted shock, and hysteria.
What I failed to do the first time but nailed the on the 2nd bot is calculate desired speed. I knew that I was going to use 6" wheels I then decided that I wanted the bot to go about a foot per second, which is actually pretty fast. the math is pretty straight forward so I won't list it but I worked backwards from the wheel circumference to calculate the needed RPM to obtain desired speed. I found a motor that ran at 96 RMP (about 4 times too fast) and reduced it through a #25 1:4 chain drive train to reduce the speed which added a lot of torque. I kept trying to be a real engineer and calculate the exact motor size and torque desired but every time I did I only found new motors that cost $80+, I settled for a slightly over sized motor for $17ea.
The hardest thing you will run into is connecting the motor to the wheel/gear/sprocket. I have access to a lathe which helped out a ton. All of the sprockets that I found were 1/4" shaft size... intended to be drilled larger as needed. I had to bore out one sprocket slightly to fit the motor and bore out another to fit the 1/2 wheel shaft diameter. there is more than one way to grandmas house, so remember the K.I.S.S. method. and
good luck .
sorry for being long winded!
Dave
check out my site it's not quite ready for the public but what the heck!
http://www.powerroad.com/davesrobolab/Security Robot.htm
Post Edited (Dgswaner) : 4/14/2007 7:08:31 PM GMT