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Possible Rad Project, What Do I Need!?!

Comments made by my parents suggest i'm getting a rad for my birthday june 14(celebrating sooner)
So I want to have a plan in place for what ill need to make the rad.

Diagram of possible rad


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#2  
Still don't know what ill need.

Im thinking ill extend the neck to add pan and tilt abilities.

So what i'm thinking is:
Head- 2 normal/ 2 micro servos(micro or normal?), camera

Arms- 2 normal/2 micro servos(Micro or normal?)


What should I do with the gun? How could I control it?

And should I add micro servos to the shoulders to make it possible for it to grab things?

Dylan.
United Kingdom
#31  
Melvin runs for hours on one charge. In fact, it has been at least a month since I last charged him (a lot of that time he has been off but I have also done a lot with the LCD and script testing, sneezing, sleeping, blinking etc.)

However, one thing you need to be aware of is that LiPo batteries do not like undervoltage, i.e. if it drops below 3v per cell the battery wont charge again. It's a good idea to add in a LiPo monitor circuit & script and possibly an auto cutoff.
#32  
that's what I don't like about lipo batteries. they require a fair bit of safety.:P
United Kingdom
#33  
But they are cheap and you will only let one undervolt before you realise what you need to do:)

Charging needs safety but follow the instructions and it's safe, I charge mine unattended because I'm that confident - so confident I risk £135,000 (~$205,000) of house. I do use a fire proof charging bag mind you, I'm not that stupid:D

Go with LiPo, I cannot recommend them enough.
#34  
as ive said, I normally put my trust into ni-mh batteries. I cant entirely trust lipo batteries as I feel that just using, then charging, then using, then charging without any extra supplies or work is normal. lipos as you said I need a fire-proof bag, and I can't allow under voltage(what is that by the way) at all. I don't feel that its worth my while to deal with these batteries.(or time bombs, what ever you think.)
United Kingdom
#35  
Under voltage is when you run the battery too long and the voltage drops below around 3v (I think it's .7 or 2.8 actually, I work on 3v to be safe). Basically, when you use a battery the voltage will drop when it's discharging, the lower the voltage the lower the power left in it. So LiPo start off at 4.2v per cell, over their discharge this drops, which is how you can measure the charge left in it.

If you use the script and circuit I did the tutorial for you will know when you need to charge, throw in the auto disconnect circuit (I haven't tested it yet but the theory should work and I have seen similar circuits on other forums) and you're safe. Use a decent charger with safety cut offs (most chargers unless you buy very cheap from dodgy places) and charging is safe, I didn't used to use the charging bag, I only use it now because it come free when I bought my last 2 LiPos. It's now part of Melvin so it's no extra hassle.

FYI, short out a NiMh battery, +ve to -ve with no load and tell me they are safe:D - Do not do that really!
#36  
@techno pro , under voltage means you run the battery till its completely dead. With a lipo its found to be best for long life ( hundreds of charge cycles) to not let them completely go dead before they are charged again. the recommended voltage is 3.7 volts per cell. 4.18-4.2 volts is considered full charge. A lipo requires the same safety and respect you "should" be giving a NiMH battery when charging. So please don't buy a NiMH battery just to ignore the basics in charging / discharging safety.
United Kingdom
#37  
3.7v? I thought it was 2.7v or 5.4v for a 2S...
#38  
The "2s" designation indicates the amount of cells. 2x 3.7 = 7.2 volt battery base voltage 8.4 charged. 3s is 3x3.7 volts =11.1 volts base voltage and so on..
United Kingdom
#39  
I may have misunderstood. When you said 3.7v is that the lowest voltage to take it to? Before it starts to damage the cells? Because I thought it was around 2.7v when it undervolted. If its 3.7v I need to change my scripts.
#40  
At 2.7 volts you have already reduced your batteries overall life. The goal is never under 3.7. 3.4 its not the end of the world but also not the healthiest level for your battery. I believe turnigy considers the cells permanantly damaged and should not be used in a aircraft at risk of failure at 2.4-2.6 volts. The lower you go under 3.7 the worse it affects the ability to retain charge. After even one significant under volt scenario you have reduced the mah capacity forever. It has to do with the lithium beginning to form crystals.
#41  
Hey if you cut it off at 2.7 then at least its above the "permanently damaged and reduced capacity" point;)
#42  
There's are tons of arguments about how much each under volt affects the overall life. Here on rcgroups they suggest you have reduced your battery life to 80 percent at 3.5 volts but I don't think they have tests to confirm that.
http://www.rcgroups.com/forums/showthread.php?t=190495
I have read of people using them in planes and running them down to 3.1 volts but then they only get around 30 to 40 cycles of life through them which to me sure feels like a significant impact on the longevity of a lipo.

@rich it doesn't sound like you have been through more than a cycle or two , just adjust it for 3.7 volts in the future and you will max the possible future life out of them. Happy batteries lol
United Kingdom
#43  
Undervolt batteries will not charge, at least not on any decent charger, they will error and refuse to try.

Just checked it on google and a bunch of RC forums and 2.7v is the absolute minimum, most claim 3v so even the cheaper LiPos don't undervolt. Retail protection circuits hard cut off at 3.0v and soft cut off at 3.3v. Everything I found suggests a low level cut off at 3.3-3.4v

Where did you get the 3.7v from since everything I just read (and remember reading when I was making the LiPo monitor script) seems to say otherwise (3.3v to give that wriggle room before damaging the cells).

In case it's not apparent, I'm not arguing it:) It's just I have provided people with scripts etc. for shutting off or warning on LiPos and since it's other people's batteries I want to make sure it's all OK. I'm not worried about my battery, I have only charged it once and then I don't think it was even that low. What I don't want is to have a lot of angry people coming on because of a script I provided
#44  
how can I tell that a lipo battery is going to undervolt and how can I prevent it the cheapest way?
United Kingdom
#45  
Use the lipo circuit and monitor I did a tutorial on (it's linked to in an earlier post here).

It's a very cheap and simple circuit, one cell connects directly to one ADC port the other goes through a voltage divider (3 resistors), with a diode for over voltage protection on the ADC port (optional, but recommended). Then a script runs and checks the voltage every x ms, the discharge rate isn't too bad so every 500ms or even 1s would be fine. If it's getting low it tells you, it can shut down things or even disconnect the EZ-B from the PC. It doesn't shut off the battery though so you will need to disconnect or charge it relatively quickly depending on min voltage level set.

Or, you can get balance port monitors that plug in to the balance port, report the voltage and buzz when low. They are cheap and stand alone, but don't shut the battery off.

Or try the auto shutoff circuit I posted, but I haven't had chance to test it yet. This one will shut off power to everything on low voltage but does draw current itself so eventually will undervolt the battery (would take a fair amount of time, like hours or maybe even days).

Melvin uses the monitor circuit and reports the voltage on the LCD in a similar way to the battery icon on a phone. The only time I undervolted a battery was when I forgot to disconnect it and didn't touch it for weeks.
#46  
Rich built a circuit and can show you how to monitor it on your ezb. He's very talented with script.

@Rich, I use to be into rc cars and planes. I've always stayed with the 3.7 volt rating from the factories but lots of individual hobbiest like to push the equipment as far as they can before something noticeably bad happens. 3.7 is what I have stayed with and worked very well to maximize battery life. I use to work for horizon hobbies and we tested all kinds of stuff , even melted just about every lipo bag too. To be safe I would have the script stop at 3.7 volt. Thats my suggestion. I realize that others claim various voltages but for me its safe over sorry lol.
United Kingdom
#47  
That's good enough for me:) I'm not 100% sure what I put in the script anyway, I know it's a variable at the start so the user can set it themselves if they want to risk going lower but it's always good to have good values as defaults.

Edit: Just checked, it's set at 3.7v for low and 3.5v critical anyway which should be OK depending on the current draw of the robot and circumstance.
#48  
now for me to do all that, slim. I barely understood half of what I just read. Yes lipo batteries are awesome for life, but the care you have to take with them is to far out of what I think of as my standard.

I would love to use lipo batteries but I just dont have the patience and/or understanding to work with them.

@jstarne, Ni-mh batteries you can drain completely, and charge from anywhere in its power level.

On another note, what is the next best battery?
#49  
I thought that NiMH batteries should not be discharged lower than 1 volt. When a group of cell are wired in series and one cell drops below 1 volt it may not recover and charge with the proper polarity. In other words the cell becomes reversed.

A good second choice would be Sealed Lead Acid (SLA) batteries.
#50  
I don't know robot_Doc. I put my trust in ni-mh batteries anyways.

Here are the Final plans for the rad.

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