Electrical questions about my robot

Hi Braedan,

The short answer to your first question is that one load will not affect a second load. In reality the motor may load the line and lower the voltage slightly which may slightly decrease the current to the LED but you may not notice it. This loading effect can be minimized but having low resistance wires and connections from the power supply to the loads. The position of the loads will not make much difference if the resistance of the supply lines is low. Think of how you can turn on multiple lights in your home with out a noticeable effect. Also note that when a large appliance turns on the lights may dim. This is the resistance of the supply lines having to be factored into the equation.

John

Hi Braedan,

I will think about your other questions. The battery type that you mention is very good for delivering higher current and for the ability to be recharged. 7 aH basically means that you can expect about 7 amps for one hour though reality will probably cut this down. The equipment that you hope to hook up to this battery is quite ambitious. The 100 Watt 12 volt motor alone will draw over 8 amps. I would recommend that you brush up on the math for figuring currents and wattage so you can plan ahead and not waste time and money on batteries or motors that are not compatible. Here is a link to a tutorial on Current and wattage calculations.

http://www.electronics-tutorials.ws/dccircuits/dcp_2.html

John

just a few thoughts, Braedan:

You should definitely use a buck converter for the circuits other than the motors. Since the motors will be 24 volts and other circuits will be 5 Volts, the basic power supply (batteries) will be two 12 volt batteries in series. By the way it is not a good idea to use lead acid in parallel since they will self discharge over a relatively short time compared to lithium for example. Since you will use a buck power converter for the lower voltages there will be no noticeable change in the LED brightness. A large capacitor will smooth out the power surges but it will probably not be a factor since the surges will be the result of the motor turn on and they are pretty tolerant to small voltage changes. This is especially true for stepper motors. 

Q1 - Ideally one load does not effect the other. In reality many things can happen. For instance, in your example provided, the motor, or any inductive load, will produce an EMF that will likely feedback onto the rail unless some form of protection is used. In your instance you would need to isolate the motor from the rest of the circuitry. Another situation is called LOADING. This is when you try to pull too much current from a supply, based on its power rating, and the output voltage drops. The more you experiment, the more you will see and learn. The more things you hook up to your rail, the more you have to be aware of what might be happening.

So.

i have been been doing some research and now know a little more about decoupling. I found this circuit (attached in image) for decoupling an IC. I was wondering if this could be repeated for all 37 IR sensors in place of the IC shown in the circuit. If not could you recommend an new circuit diagram, or maybe better capacitor choices for my needs, thank you!

website:De-coupling

Sorry I couldn't post  the images but they are on the website I linked.

Hi Braedan,

You have an ambitious plan and I highly suggest you find someone local to help you with the electronics.

Most drive circuits use either a constant current device and or a nice capacitor bank to keep spikes along the voltage lines to a minimum.

I am not sure why you need the 36 sensors, but I need to ask if you intend to keep them all working at the same time?

If you have the time budget, you can set up a sensor firing sequence, which will greatly reduce you current demand and reduce any interference as the various devices pull in their current.

I would use a capacitor on each sensor, probably just the 1 microfarad or so.  That will keep each sensor from experiencing induced spikes.

Make sure that you set up diodes around your motor leads to prevent induced currents as you use the motor.  A motor not only uses current, but it can generate current if the wheels continue to move after the power is shut off.  Very bad!

If you take some care in equalizing the load as I have suggested, your 12v battery should be up to the job, depending upon how often you use the motor.

I would also recommend that you use a microcontroller to establish use logic to step through the sensors and analyze the data as it comes in.

Keep in mind that each sensor will need time for the pulse to go out and return to get your distance measurement.

Over what distance are you expecting to measure?

The more information you provide us on your proposed circuit and circuit board implementation the more guidance we can provide you.

Is this a school project or just something you want to do?

DAB

Hi Braedan,

Your images came through just fine and the link you used went to a good article on decoupling. Yes if you put your sensors in place of the indicated IC you will provide the decoupling that is recommended. Getting the .1 uF caps close to each Sensor is important and make sure they are across the power supply leads and not attached to any of the signal leads unless recommended by the data sheets. The use of the 47 uF capacitor helps keep the volatge from dipping in the line when the sensor turns on. I would not use an individual 47 uF for each sensor as this will put 1700 uF of capacitance on the power supply rails and this would be excessive. Depending on the power supply or buck converter used to supply the 5 volts I would look at the recommended output capacitor size and provide this amount in 4 or five seperate caps. For example if the converter recommends 100 uF capacitor you could use (5) 22 uF caps. These larger caps should be electrolytic caps and the small 0.1 uF caps ahould be ceramic.

John

Hi Braedan,

The article that you linked to shows a picture of a small ceramic capacitor labeled 103 but he article talks about a 0.1 uF capacitor. I feel that the 0.1 uF is the correct size and the one marked 103 (which is actually 0.01 uF) may be a little small. Your data sheet may have a recommendation which is best followed.

John

I'm also curious about why there is a need for 37 IR sensors.

I've seen other robots use a servo with a single sensor mounted which covers the area ahead very well.

A lot of the sensors have an onboard regulator so it might be worth checking out one first.

Personally I'd be splitting the 5v rail up if you need to have that much load.

Your query about current and rails is best referenced back to water.

The river flows at a certain speed (ie voltage) and has a number of pump which draw 100 litres/minute (ie Amps).

If the river is not wide (or deep enough) then the flow will slow to a trickle (ie the voltage will drop).

If the river is wide enough to handle the pumps then there will be no effect.(ie your LED will shine just the same).

Every piece of wire has some resistance, and like a normal resistor as current is passed through this 'resistance' there is a corresponding voltage drop.

The aim is to ensure your distribution loss is minimal and this includes the wires and connectors.

Mark