Wobble Bot

Question

I have decided to build a single wheeled bot and im keeping it simple, since this is my 1st build. No arms, no servos(other than for the wheel), and no body covers. So, it will be no wider than the ez-b board and no taller than a tire, servo, board, gyros, and battery pack. I'm going to use two futaba gy401 gyros, one I have already purchased. My issue is this: I'm unsure of how I will attach the gyros to the server and then to the board. I have a design in mind, but I'm not sure how to design the wiring. Any help is appreciated.

Oh, and I want to control the bot with a wimote.

Thanks

jstarne1 · Answer

Alright cool, thanks for making a thread. Ok you want to do a smaller balance bot so you should be able to utilize some smaller gear. What do you have so far for your build?

CRich · Answer

I have the ez robot builder kit, some spare wire, connectors, sodering iron, and soder. I have purchased one gyro and a gear kit from vex robotics. Both are still on their way.

jstarne1 · Answer

Whats the gear kit for? Here is a physical layout pic.  This is a simple design , three circle solid pieces and one ring at the bottom. One shelf for batteries next shelf ezb and 2 h bridges and gyros. Top is left clean but thats a great place to piut a ez cam

CRich · Answer

I order the gear kit before I decided what I wanted to build. That looks like what I was thinking. What do you mean "3 circle sold pieces"? Why are there 4servos?

jstarne1 · Answer

I meant solid circles , another words no hole in the platform. The last piece goes around your ball. The servos are modified to be able to rotate continuously and controlled by an h bridge. L298n 2.5 amp in the ez robot store. Two servos rotate x axis and two the y axis.

CRich · Answer

Also, if I use the supplied servos (the ones that are in the kit) why do I need a h bridge?

jstarne1 · Answer

You need four so thats two more of the 10.99 servo  For your robot to have good grip on the ball you need a motor with a wheel on each end of the axis agianst the ball. So you have two already you just need two more to balance on the x and y axis.

CRich · Answer

Oh, lol. I get it now. Ok, so what do you think about using a racketball?

jstarne1 · Answer

Oh and if you want left right twist you could get and extra two servos but that. Axis is already balanced so it doesn't need a gyro. Im going to draw out how this plugs up. The reason why you need a h bridge is because the gyro connects directly to h bridge and will feed it signals to stay level. This does not require programming only adjustment of the gyro trim and sensitivity and you let it do its job. Then when ezb feeds it a signals the robot moves in that direction portional to the input signal to the gyro. Rc gyros are setup to be inline. Because the rc servos can be used straight up as a geared motor by removing their controller and soldering leads. This insures they arent drawing power from ezb and the h bridge and feed the servo power it needs to adjust quickly. Also I would run the servos at 6v

CRich · Answer

I have one h bridge. So, I need to order two more servos and one more h bridge

CRich · Answer

Ok, I'm following...so far. Twist or strafe would be kind of cool.

jstarne1 · Answer

Twisting? You ask and you shall recieve!

jstarne1 · Answer

Diagram make sense?

CRich · Answer

Yea, it does. So to be clear, I only need one h bridge, correct? I can use any port on the h bridge I want as long as I tell the software which one I'm using, correct? Where on the h bridge will the gyros hook into?

CRich · Answer

Is there a particular online store you use for structural components?

jstarne1 · Answer

Ill update the drawing. Yes 2 h bridges and if you want side to side twist you need to pick up two for that side to side motion. If you dont want side to side twist you wont need the second h bridge. Ok so heres parts list so far assuming you do the twist.. Ezb 6 cont servos (2 you already have) 2 l298n h bridge 2S lipo battery Ball caster ( for center load) 2 futuba rc gyros 6 servo spline tires ( you can use ones that come with ez robot cont servos but there are omniwheels that will allow twisting action smoother i believe) A ball, mini basketball works great at around 20 psi Servo ext cables , about 20 should do

CRich · Answer

Like these wheels: https://www.vexrobotics.com/products/accessories/motion/276-1902.html How many volts for the battery? Do you think the ball inside the caster be roughly the same size as the wheels I use?

CRich · Answer

Or, maybe these wheels. https://www.parallax.com/tabid/768/ProductID/647/Default.aspx With a 3/4" ball caster

jstarne1 · Answer

I like the ones from parallax because theres smaller gaps between rollers. However the vex are cheaper because they come in a two pack...... just get the vex those will work. The battery is 7.4 volts which is what 2s means. Also one part I forgot is a regulator to keep voltage to the motors 6 volts so they dont over heat. 7.4 volts of constant use could overheat them. Members here regularly use step down converters and so do I. You need 2 one for each h bridge. https://www.ebay.com/itm/DC-DC-Buck-Converter-Constant-Voltage-Voltmeter-Ampere-Meter-Greeen-LED-Display-/140873010255?pt=LH_DefaultDomain_0&hash=item20ccaf8c4f

jstarne1 · Answer

By the way a racketball is way to small to fit your equipment on. How about a glowing ball? 8 inches is ideal for a small bot but enough room to fit the wheels and such. Also servocity.com sell abs plastic but honestly I would go to home depot and cut all this out of 1/4 inch ply. Its light cheap, and easy to cut and glue on.

CRich · Answer

Ah, ok. So the step downs will go b/t the H-bridge and motors? I have access to a CO2 laser and plastic so I may cut it out of that. Lemme gather some parts and I will revive this thread once I begin to build.

CRich · Answer

Oh, and a glow in the dark ball is a cool idea too!

CRich · Answer

What amperage range does the battery need to be?

jstarne1 · Answer

A 20c battery or higher is fine. Nothing special. Also the step down converter is between batt and h bridges. It steps down input to the h bridge. Alright take pictures. We love seeing projects. -Josh

CRich · Answer

Ok, I have everything that I need. Now, I just need help figuring out the wiring. Especially with the 2 H-bridges ... Pls lemme know how to hook the h-bridges to the motors

jstarne1 · Answer

Hi could you take pics of all the hardware you have so I can help further? Thanks

CRich · Answer

CRich · Answer

i also have some structural components and wire, ect.

jstarne1 · Answer

Ok cool you got everything really quick! Ok so first thing is 4 of those continuous servos gotta be setup to wire to your h bridge. Theres a controller board inside them your going to remove and wire the red and black directly to the motors power tabs. Do this the same for 4 of those servos and be sure to connect in the same polarity so you dont have one go in reverse. Basically you are turning the servo into a quick geared motor. Test each one with direct 6 volts... once those are done onto the next step. Next you need to adjust your step down converters to be 6 volts on the dot. This will provide the regulated 6v to your modified servo motors. Once these are calibrated , next step

jstarne1 · Answer

Normally you connect the h bridge directly to ezb but you need to put the gyro inbetween each one to balance on that axis. Let me find the h bridge tutorial...

jstarne1 · Answer

Ill try to draw something but basically your plugging input into ezb and output onto h bridge . You will need to split the signal to both sets of input pins because both motors on each axis must move together and at the same time.

jstarne1 · Answer

Before installing the gyro consider using pwm control and interfacing that with wii mote. First things first get those 4 servos modified as just geared motors.

CRich · Answer

Ok, I should be able to tackle some of that this weekend. Thanks, I'll keep you updated!

mattbrailsford · Answer

Oh man, this project is so cool. Looking forward to see how it goes. Josh, could standard motors be used instead of servos if you are just running them as geared motors anyway?

jstarne1 · Answer

Sure you can use standard motors if they have enough torque. The continuous servos are so cheap its easier to use them for a small project like this.

CRich · Answer

motors wired Can you please elaborate or illustrate the next step?

CRich · Answer

In order to test the motors, do I need to hook them and the battery to the easy b? I do right?

jstarne1 · Answer

Yup they are not "high torque" servos so yes you can directly connect them to ezb right now. Get your wii mote working for right now. Ive gotta find an illistration for you to wire the gyro but theres lots to do before you gotta hook up the gyro like getting wiimote working and building a frame.

CRich · Answer

Gotcha. Alright then...I will work in that some. Thanks again

CRich · Answer

So i plugged the servos I mod'd in and they run non-stop. I cant override them; they only go 1 dir and 1 speed. Am I doing it wrong? I attached them to the board and pulled up a mod servo movement panel, but everything I tried failed to alter their performance.

CRich · Answer

LOL Nm, that was a dumb question, sry. I completely forgot about the H-bridge So I'm on to the wimote --- I'll let ya know when that gets the best of me

CRich

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