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61
Mechanics and Construction / Re: Making an impossible to juggle juggling club
« Last post by MrPrezident on December 02, 2014, 05:06:35 PM »
I like the idea.  The simpler, the better.  However, I'm not sure that it would work so well.  The club spins when you throw it, so centrifugal force will push the center magnet toward the end.  I suspect that it would just hover near the end magnet the whole time.
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Electronics / Re: Accelerometer/gyro data to serial port using bluetooth.
« Last post by Seras on December 02, 2014, 03:29:57 PM »
How do you know where a resistor etc. is needed? And do you think it would be better
/easier to use serial data? (programming wise?)

Edit: Also it says this about the RFduino:
Low Supply Voltage   1.9V
Typical Supply Voltage   3V
High Supply Voltage   3.6V
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Electronics / Re: Accelerometer/gyro data to serial port using bluetooth.
« Last post by Gertlex on December 02, 2014, 03:20:53 PM »
Whoops. I completely missed that your image showed the RFDuino on the left. (I assumed it was just the layout for an MPU6050 breakout, and that you had pulled the image from a seller's site...)  I also wasn't aware the RFDuino wasn't just yet another Arduino form-factor board, heh.

Seems straight forward to just put one on top of the other, possibly with double-sided foam tape, and then solder the resistors/wires where they're needed.  I do this sort of thing commonly with my own projects.

Not sure if you can directly put, e.g. a 1S Lipo powering the RFDuino. If you can't, one solution might be this small board.

I'm not aware of a smaller MPU6050 breakout, unfortunately. But its .8" length seems like it shouldn't be too bad.
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Mechanics and Construction / Re: Making an impossible to juggle juggling club
« Last post by Schlayer on December 02, 2014, 01:26:39 PM »
This seems like an interesting project but I think there might be a far simpler solution than building a tiny robot weight mover: Magnets. I think you can probably accomplish a fair level of random center of mass movement by replacing your wooden dowel with a smooth, metal rod, and get strong disk magnets at either end of the rod and another strong disk magnet in the middle oriented to be repelled by both of the other two. Buy magnets with holes the diameter of your rod in the center so you can slide them easily all over the rod. Viola: a super-annoying-to handle-club whose center of mass semi-randomly bounces from one end of the rod to the other.
No need to worry about any fragile electronics and complicated random movement code!

http://www.mcmaster.com/#ring-magnets/=uunre1
http://www.magnet4sale.com/112-lb-holding-power-neodymium-cup-magnet-1-57-magnetic-round-base/
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Electronics / Re: Accelerometer/gyro data to serial port using bluetooth.
« Last post by Seras on December 02, 2014, 01:05:19 PM »
I haven't looked at how small the bluetooth adapters out there get, but I think they get on the order of the size of my last thumb section... I could see an approximately thumb tip sized sandwich of mpu6050 breakout | custom perfboard with basic MCU chip | bluetooth chip/board.

Other than that, I don't have a specific idea in mind, but am instead probing at your requirements to see how flexible they are...

Is bluetooth a requirement? I've had so-so results using bluetooth in practice, but also haven't personally used any wireless solutions of the size you're after.

What are you planning to do to power this small wireless IMU setup?

"The RFduino has Bluetooth 4.0 Low Energy built-in"

And it is pretty small so the only problem is to get an accelerometer on it and with its 7 io's it should be able to handle the signals from an mpu-6050 parallel?

Edit: Forgot the "What are you planning to do to power this small wireless IMU setup?" question.
I dunno just a small battery of at least 150 mAh would probably suffice for 3 hours run time?
66
Mechanics and Construction / Re: 3 wheel vs. 4 wheel, 2 motors vs. 3 motors,
« Last post by Schlayer on December 02, 2014, 11:59:34 AM »
For a first robot, I would recommend you definitely use differential drive and not go for 4 wheels. A sumo bot will need its powered wheels to be centered under as much of the robot's mass as possible for maximum traction; you might actually only want two wheels! You also would't want to add a third motor in any case, as the benefit would be minimal compared with the added complexity in your code for moving the robot. I have worked on a sumo robot project which ended up using two motors, one wheel each, and the front was just a super-sharp wedge that got underneath enemy robots and scooped them up so they lost traction. (That was radio controlled though.) If you need anything else, let me know.
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Mechanics and Construction / Re: Need Help with a Rear Wheel Drive Car Style Robot
« Last post by Schlayer on December 02, 2014, 11:47:13 AM »
The wheel/tire can always add a level of shock absorbing.

I have already tried to address this in part with my chosen wheels; they come with a sort of foam-rubber material moulded on as a tire and have different hardness-es. I got Shore 40A and 50A hardness wheels (1 pair each) and my skateboard wheels should have a hardness of roughly Shore 75A, which is not soft enough to 'give' much under such lightweight stresses. I have some ideas for adding suspension to just the front wheels already, should I stick to the skateboard wheels.

I'd be more concerned about what happens when you flip the car at 30 mph (or 10 mph even).

Yeah... I was thinking of buying some 1/8" aluminum dowels and bending/cutting them into a sort of roll cage, but there could be a more elegant solution. I will probably use foam tape to add a nice cushioned bumper in the front and rear for lower speed collisions. If you have a better idea for a body protection method, let me know!

(I'd suggest splitting up that giant paragraph into a few coherent pieces. I might have had ideas while reading it, but lost track of them in keeping track of where I was in that paragraph...)

This has been addressed, thanks for the warning.
68
Electronics / Audio Robots...
« Last post by dynamix on December 02, 2014, 07:15:50 AM »
ArcBotics Sparki Robot this is the name of the robot I am purchasing to begin. Mainly because it is for my daughter but i Also want to start learning and build my own robot moving forward. That's my introduction here, taking small steps into a much bigger world. What inspires me is the personalities of the robots in Star Wars. Now I know that is just a movie and I don't expect to get a speaker and mic attached to a robot and have an instant personality but that is my goal to learn how to program personality robots. My first personality robot goal is to make something similar to R2D2 meaning simple interactions and not deep conversation like C3P0. I am mainly curious right now what would I have to buy to attach to a robot that would give it a programmable audio channel. Mono is all I need and a decent speaker so you can hear the sound clearly. I don't expect to do this tomorrow and will start with the simple Sparki and move onto other simple kits before I attempt to do anything more creative. Thanks for your patience, I am a noob and any kits you recommend I'll definitely try. Also anything to improve my coding skills which is none right now but if theres books or college courses I'm in for the long haul.
69
Misc / Re: Solar robot question
« Last post by Schlayer on December 01, 2014, 11:00:24 PM »
I'm not a prolific programmer and as such I cannot possibly definitively say whether or not that last art is doable, but in terms of purely hardware limitations but probably is. As for the rest of your question, all you need to do is a little code magic!
Outdoor solar lights often include a little photovoltaic cell (the solar cell) with a photo-resistor or photo-transistor (the light sensor) in the middle. This setup provides two key things: 1) The light knows when it is dark and turns on only then. 2) When the light is not on, it is always due to the fact that there is enough ambient light for the battery to charge.
So, you have a micro controller and you programmed in some digging routines for one specific robot (we'll use a single one for this example since it's literally repeating the same thing for each). You set it up such that your robot will always be digging or, realistically, until the battery drains. Your battery is hooked up to a little solar cell/panel and to the controller so the electricity from the cell ONLY feeds into the battery and the battery ONLY feeds into the controller; the other servos, motors and whatnot will be powered from the controller since we're talking smallish scale toys without high current or voltage requirements.
The hard part: electronics theory.
Photo-resistors change their electrical resistance in response to ambient light levels. A photo-resistor starts out with high resistance in the dark and its resistance drops as the light level increases. Photo transistors also respond to light levels, but for your controller it's easier to deal with simple electrical resistance changes since Ohm's Law (V = I*R) since your controller should be able to measure precise voltage differences through the photo-resistor. Whatever type you buy, you'll need to use the controller to find some baselines for light levels affecting the resistance. What light level is low enough that your solar cell no longer generates any current? This can be considered your 'daybreak'. What light level is what you want to call 'night' and start your digging process? What light level will you call 'day' when you stop digging? All these will need to be experimentally determined and then used as arbitrary resistance values for your code.

If this seemed like a super dense block of nonsense, the key info is that you have to make your robots act like outdoor lights and respond to variances in light levels to determine when to be digging or recharging. If you wanna get more complicated, you might be able to figure out a way to check your matter voltage using the controller and set the robots to stop digging whenever they go below a certain voltage/get too discharged. This would be a nice feature in any case, but if you are using Lithium batteries it would be essential as they can get damaged beyond usability from being discharged too much, and if you try to charge a damaged Lithium battery it may melt or explode. This is not very good for flesh, and certainly not for your robots.
I strongly recommend Arduino for you controller boards as they use an easy language to program, run off any computer OS, and are pretty cheap and reliable.

Last thought: if you were to implement this whole day/night cycle idea in your robots, using the laser or other light source aimed at the robots would be pointless since it would trip the photo-resistors and make them all turn off again. Much simper than aiming a laser is just bathing the whole area with flood lights, though it would look far less cool. The you would't have to worry about ever turning the robots off so long as the lights can keep powering them!

If you have any questions, feel free to message me :) I'll probably get back to you within a few hours.
70
Electronics / Re: Accelerometer/gyro data to serial port using bluetooth.
« Last post by Gertlex on December 01, 2014, 07:48:31 PM »
I haven't looked at how small the bluetooth adapters out there get, but I think they get on the order of the size of my last thumb section... I could see an approximately thumb tip sized sandwich of mpu6050 breakout | custom perfboard with basic MCU chip | bluetooth chip/board.

Other than that, I don't have a specific idea in mind, but am instead probing at your requirements to see how flexible they are...

Is bluetooth a requirement? I've had so-so results using bluetooth in practice, but also haven't personally used any wireless solutions of the size you're after.

What are you planning to do to power this small wireless IMU setup?
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