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H-Bridge Recommendations And Voltage

I am going to need 2 H-Bridges for my robot, one for forward, reverse and turns. and one for raising and lowering the robot. Do they make an H-Bridge that can do dual functions or do I have to use 2 bridges. I am trying to keep the amount of boards in the robot to a minimum.

Second question is the motors on this robot are 7.2v and I know I can get a re-chargeable battery that is also 7.2v at 3800 mah, I am still tying to understand the voltage thing. Is 3800 mah the same as 3.5 ah and how long does a 3800 mah generally run on a full charge. I see allot of batteries out there with different mah ratings so it would be better to understand these ratings. I don't want to get something that although is the same voltage but a higher mah rating and burn out the motors or the EZ-B

Thanks for the help and just so everyone can see the robot platform I am using here is a video of it.

*confused*

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Synthiam
#1  
Milliamp Hour (mAh)

Milliamps Hour (mAh) is important because it's the easiest way to distinguish the strength or capacity of a battery. The higher the mAh, the longer the battery will last. Batteries with different mAh ratings are interchangeable. If your battery is rechargeable then the mAh rating is how long the battery will last per charge.

Milliamps Hour is 1/1000th of a Amp Hour, so a 1000mAh = 1.0Ah

Think of a cars gas tank. Voltage is how much gas is being used, and mAh is the size of the gas tank. The bigger the gas tank (mAh) rating the longer the device will run. If your battery is rechargeable, then think of the gas tank as refillable (rechargeable).


Hope this helps a little something i found on internet.
United Kingdom
#2  
If the load is 1A then a 3800mAh battery will run for 3.8h before running out. If the load is 3.8A it'll run for 1h before running out.

So work out your load in mA. Divide the battery rating by the load. i.e. 3800mAh/1000mA=3.8 Hours. 3800mAh/742mA=5.12 Hours. And so on.
#3  
Thanks for the great info everyone. Last question can I tie 2 batteries together to get a long run time and how would it need to be wired.
Thanks again
United Kingdom
#4  
Yes.

In parallel, red to red, black to black.
#6  
Watch your polarity designations........ Black leads are normally ( - ) and positive leads are ( + )
#8  
For your original question, there seem to be precious few 4 motor H-bridges out there, so the simplest would be 2 H-bridges. The one for raising/lowering you would want an R/C (vs serial) one so it looks to EZ-B like servos not a movement panel.

Another option (and one I will be investigating for my big bot that will have at least 1 5-motor arm) is to use R/C ESC's, which essentially turn a motor into a modified servo. It would be more devices (one per motor) but they are small and cheap. However, most need brushless motors, and most can't go directly from forward to reverse without a stop in between, so investigate and purchase carefully. I wish I knew more, but I have other priorities before I get to this, so I haven't looked too deeply yet.

Alan
#9  
There are only 2 motors for raising and lowering (1 per both front and 1 for both rear tracks). I may be wrong so please tell me, but if the R/L (raise/lower) motor in the front is on one of the H-Bridges connection and the rear R/L motor is on the other connection it would be no different then if I set it up like the forward and reverse-correct.
Thanks
#10  
Yes, sort of... You can only have one Movement Panel in an EZ-B project, so your drive wheels should be a movement panel, and your up down controls will need to be scripted or "servo" controls.

Alan
#11  
Thanks Alan, what RC one would you recommend, these are not brush-less motors.
#12  
I would let someone else make the recommendation. There are a lot of options, and I haven't personally used any yet (I have a Sabertooth 2x25 which is overkill for your environment. A 2x5 would work, but I am sure you can get a better price point.

See this thread for an interesting option: http://www.ez-robot.com/Community/Forum/posts.aspx?threadId=3475

Alan
#14  
Yes, that kind of thing would be perfect. I didn't mention earlier, but you can also use a 4-wire (really 5 with PWM) like the 2.5 amp controller that DJ sells, but it takes 5 digital ports where servo emulation only takes 2 for the same job.

Alan