Questions from a first time builder.

[TheGreenMonkey]

Hello all,

Firstly I would like to thank everyone here for the extensive guides and how-tos that are posted here. I have spent the last 15 hours lurking on the forums and guides. I come from a fairly strong RC-Car/Truck background and this will be my first foray into robotics(I think this counts).

The Project: A computer case mod that will entail a drivable chassis and a controllable turret mounted on top. The turret gun is a Vulcan Nerf Gun. This originally was going to be an RC project, but my roommate and I are really wanting to drive/shoot it with app on our Android OS phones using the Bluetooth connection. The project, I am estimating, will weigh about 30lbs. It will go about 2-5mph.

The Features I Would Like the Project to accomplish:
Locomotion- Chassis will have tank treds, so I need to be able to operate each track separately so it can turn.
Turret pivot and tilt- I would like the turret mount to be able to turn side to side in about 300 degree arc. The tilt feature is kind of secondary. Mainly because I am not sure on how to make a tilting, rotating mount. If I can figure it out though, I am looking at 10-15 degrees up and down.
Firing and Targeting- I want to be able to turn on and off a targeting laser that would be barrel mounted on the turret and to be able to fire the gun.

Plan:
First- Build project as a RC device first, to make sure all of the mechanics of the all of the features work correctly. I figure this is the best way to actually build the chassis and fabricate the motor mounts and housing properly instead of troubleshooting mechanical issues on top of my Bluetooth issues.
Second- Rewire the project to use Bluetooth controlled by a Bluetooth Dongle on a laptop.
Third- Develop phone app to emulate coding that was fine tuned on the computer. This would be my first attempt at making an app as well, but I'll cross that bridge when I come to it.

My Questions: Basically I am needing confirmation on what electronics I will need to accomplish a Bluetooth controlled device. From the Bluetooth How-To guide, I read that I would need a Bluetooth module, like this http://www.sparkfun.com/commerce/product_info.php?products_id=158 and a microcontroller. Is that all I need? Besides the obvious things like power supplies and motors. What kind of microcontroller do you suggest? Should I build one or are the ones that are already out there that would be easier/cheaper. Do I need any further electronics to control the locomotion and and turret or could I plug everything into the microcontroller? Also since the main portion of this build is a computer, do you think that the electric motors will affect anything inside the computer? Harddrives etc?

Thank you for your time, I know I wrote a lot. I just wanted to give a detailed breakdown, so that people can get exactly what I am going for.

-TheGreenMonkey

[Razor Concepts]

Arduino!

Computer USB > Arduino > peripherals (bluetooth, turret, etc etc)

You can simply search "arduino bluetooth" or "arduino servo" and get tons of examples, so if you can code reasonably, it shouldn't be too bad.

[Cristi_Neagu]

Axon!

Yeah... we could do this all day and not get far.
Best advice you can get about choosing a controller: have a look at the Axon (a helluva lot of functionality) or the Arduino (very good price from what i hear. There are other cheaper controllers on the market if these are too much for what you need. After you did some scouting, decide for yourself what works for you. Don't ask which one you should use because you won't get a clear picture. You should ask what features do individual controllers have to offer.

For the power supply, you should use the computer's power supply, but it will require some electronic magic because it delivers 12V and you need 7V or whereabouts for servos. A LDO regulator should be employed if the board you decide to use doesn't use one.

The turret will most likely be powered by a servo, which plugs directly into most boards. Also, the Bluetooth device plugs into an UART port (so your controller should have at least one).

For the motion part, i recommend DC motors because i don't think servos would be suitable for movin a large computer around. To drive DC motors you need H-bridges. You could build your own (some very good links on this forum, and Google produces good results as well), or you could buy one (Sabretooth would be a good place to start).

That should get you moving in the right direction. I don't know how good my ideas are, but i'm sure others will have a word to say about them

[Conscripted]

For the power supply, you should use the computer's power supply, but it will require some electronic magic because it delivers 12V and you need 7V or whereabouts for servos. A LDO regulator should be employed if the board you decide to use doesn't use one.

7V from a pc power supply shouldn't require any magic at all. I believe if you plug into the 5V and 12V connections you get a 7V difference in potential. No LDO regulator needed.

Good luck with your project. I would love to hear about your progress. I'm in the process of building a treaded chassi with a defender airsoft gun mounted on top. I've asked questions here on how to connect a laser to a microcontroller and power the firing motor.

Conscripted

[TheGreenMonkey]

Thank you for the replies!

Arduino!

Computer USB > Arduino > peripherals (bluetooth, turret, etc etc)

You can simply search "arduino bluetooth" or "arduino servo" and get tons of examples, so if you can code reasonably, it shouldn't be too bad.

I was actually looking at the arduino bluetooth, the only thing that I wanted to clarify about it was if the bluetooth was something that could be constantly communicated with, or if it was just for syncing purposes. I want to be able to control the  computer in realtime like an rc robot but using the bluetooth instead of radio.

Axon!

Yeah... we could do this all day and not get far.
Best advice you can get about choosing a controller: have a look at the Axon (a helluva lot of functionality) or the Arduino (very good price from what i hear. There are other cheaper controllers on the market if these are too much for what you need. After you did some scouting, decide for yourself what works for you. Don't ask which one you should use because you won't get a clear picture. You should ask what features do individual controllers have to offer.

For the power supply, you should use the computer's power supply, but it will require some electronic magic because it delivers 12V and you need 7V or whereabouts for servos. A LDO regulator should be employed if the board you decide to use doesn't use one.

The turret will most likely be powered by a servo, which plugs directly into most boards. Also, the Bluetooth device plugs into an UART port (so your controller should have at least one).

For the motion part, i recommend DC motors because i don't think servos would be suitable for movin a large computer around. To drive DC motors you need H-bridges. You could build your own (some very good links on this forum, and Google produces good results as well), or you could buy one (Sabretooth would be a good place to start).

That should get you moving in the right direction. I don't know how good my ideas are, but i'm sure others will have a word to say about them

I will do more research on the controller aspect to decide which best suits my needs. I can not use the computer's power supply because the computer will not be plugged in when it is moving. Thank you for bringing up the hbridges, for the motors, I had missed that. You had suggested a servo to control the turret pivot, the gun is roughly 6lbs unloaded would that be too much weight for a servo? Would I be better off using another dc motor?

For the power supply, you should use the computer's power supply, but it will require some electronic magic because it delivers 12V and you need 7V or whereabouts for servos. A LDO regulator should be employed if the board you decide to use doesn't use one.

7V from a pc power supply shouldn't require any magic at all. I believe if you plug into the 5V and 12V connections you get a 7V difference in potential. No LDO regulator needed.

Good luck with your project. I would love to hear about your progress. I'm in the process of building a treaded chassi with a defender airsoft gun mounted on top. I've asked questions here on how to connect a laser to a microcontroller and power the firing motor.

Conscripted

This build is more for transportation of the computer and mounted artillery :-p So the computer will not be powered on while the robot is in motion so I can not draw power from the computers power supply.

I plan keeping the gun detachable so the gun is going to retain its own power supply along with the laser. So I can't help with hooking up the firing motor laser to your microcontroller. I just want to be able to remotely fire the gun and turn on the laser. I do plan on doing a full picture/video build so you will be able to keep track of it.

[Conscripted]

I plan keeping the gun detachable so the gun is going to retain its own power supply along with the laser. So I can't help with hooking up the firing motor laser to your microcontroller. I just want to be able to remotely fire the gun and turn on the laser. I do plan on doing a full picture/video build so you will be able to keep track of it.

I've got it all worked out how I'm going to power my airsoft gun and laser. I only mentioned it so that you would be aware that that information is available here.

Bluetooth is often used as a "serial cable replacement". You can send data across the link the same as if it were a physical cable. There is a good video on this site where admin uses one to send commands to one of his projects. He sends a command by pushing a button on the keyboard. That information goes into hyper terminal and comes out the other end of the bluetooth link. What you send and how you can use it are dictated by your coding skill.

Keep us posted on your project. I know I'm interested
Conscripted

[Cristi_Neagu]

You had suggested a servo to control the turret pivot, the gun is roughly 6lbs unloaded would that be too much weight for a servo? Would I be better off using another dc motor?

Even though the full 6lbs of the turret won't be taken directly by the servo, the inertial load is quite large, meaning that the servo will have a hard time trying to move and stop the turret. I don't have that much experience with servos, but someone might suggest one strong enough to move your turret. If it doesn't work, you could either use a modified servo (with continuous rotation) coupled with a gear box, or a DC motor, most likely with a gearbox again.
The advantages of using a servo are:
- ease of control (to make it go left or right you just need to vary the duty cycle of the signal, which means just one control line; DC motors use at least 2, or 3 if you want PWM control)
- ease of wiring (you just plug it in your controller board; DC motors need an additional H-bridge along the way)
- autobraking (when you tell a servo to stay centered, it stays centered (i think); once you stop the power supply for a DC motor, it's free to spin every which way)

Obviously, if a servo isn't strong enough to move that turret (but using a gearbox, it should), you have to use a DC motor. It will take a bit more space on your controller, and require a H-bridge. If you're using a gearbox with it, the gear ratio might be big enough to ensure autobraking.

Now we just need someone with more servo experience to pitch in.

[Ro-Bot-X]

This servo should be strong enough. In fact, i think you can use a couple of them modified for continuous rotation to drive the PC around. At 6V, these servos will need 2A current at stall for 12kg.cm torque. Cheers!

[HyperNerd]

Does the PC have to have all its electronics in, or could you just use the case? If you only need the case, I suggest putting as much as you can inside the case to provide some protections from dust / small gravel etc.

As for remotely firing the gun, you best bet is probably to go with a powerful servo to press the trigger.

Now for a few questions:

How much force (roughly) is required to fire the gun?
Is it an electronic trigger (a button which activates a firing motor) or a mechanical trigger (trigger linked directly to the firing mechanism through levers)?
Do you want the gun to be fully operational when it is removed from the vehicle?

Looks to be a pretty awesome project, can't wait to see some pics of the build

 -HyperNerd

[Ro-Bot-X]

Do you need the robot to carry around it's own computer or just be sort of a carrier for any computer that needs to be transported? Do you have a computer already, or do you want to get one that suits the project? I am asking this because there are main boards available especially for embedded systems (look at the Mini and Micro ITX form factors) and they have a special ATX DC power source. Also, there are solid state hard drives and you can eliminate the DVD burner from the computer. You can find or build your own small case that is not too heavy so you don't need such powerful servos.

[HyperNerd]

Good point! A Micro ITX board would make the robot a whole lot lighter, and you could easily run one from some SLA or LiPo packs.

On another note, I did some research into the Nerf Vulcan, and it looks as though the gun weighs in at around 8 lbs (3.5 kg), which is very heavy for a small-ish robot to carry...

Also, to answer one of questions from my previous post, the Vulcan uses an electronic trigger, which means that it will be incredibly easy to modify for remote control: by opening up the case and soldering wires onto the trigger switch, a relay or MOSFET could trigger the gun electronically.

 -HyperNerd