I had a little trouble understanding your question... It's 15kg/cm at the base of an arm... the longer the arm is the less the weight the servo can lift and the more stress on the arm itself... So the answer to your question is ... it depends....

Thanks Richard,

You explained the results of my test clearly. The Ezbits held up well with about a foot long extension with a wrench attached. The servos browned out the board when the angles tilted beyond 120 degrees from center for reasons that now make sense to me.

Here's a video of my first test:

I don't want to give up on this one quite yet because this would make a cool robotic platform. So I'm curious what other options might exist. It seems I'll need about a 1.5 KG weight on the end to tilt around?

Cheers,

Bill

It sounds like your having power issues and not weight issues. Try routing your power feed around the EZB and not through it. Also make sure you power source has enough current to deliver the needed amps required to operate both the EZB and the peek power current needs of the motors your using.

Hey , I was last to chime in but I am more than willing to help. First off if you don't mind me asking. Is this unicycle really one wheel or two wheels close together? If you are ok with a tiny bit of fabrication I can share some ideas of how to get this to move like you want. You will need a couple servo city gearboxes and either steel Plate or lead to make a weight. Basically if you mount a gearbox motor on each side of the unicycle aligned with the axle then put a disk on the servo gearbox. On that disc is a heavy weight maybe 3 to 5 pounds. When the servo gearbox turns forward the heavy weight moves forward of the center axis making it lean forward gradually. It should work fine in reverse to. The real trick I imagine is turning. I can draw it out and make a parts list If your interested in pursuing that idea.

@EEGbiofeedback First, great project idea... That arm (with the wrench) is a way too heavy for the servo at the fulcrum... Either you need to reduce the weight or get stronger servo(s). Another idea is to extend out from the back of the arm's fulcrum servo and use a spring (or counter weight) to help take some of the load of that servo...

Thanks jstarne for the suggestion. It seems it would work with one gearbox servo attached to a rotating plate for turns with one attached to that plate with the weight for forward and backward motion. Though at $100 for each gearbox servo from servo City, that would be too much to spend to see how easy this is to control this thing. So no need to make me a parts list. Yes it's two wheels side by side. This is likely to make turning twice as difficult over the ones with just one wheel. Currently to turn, you first get a little forward momentum and then lean. So I'm anticipating the turns would be a series of forward and backward movements until it has turned the desired angle. The auto positioning features in EzScript would simplify this significantly.

The idea of having heavier and lower weights would make this work with a basket above the weights, which was my intention for this. Currently the long vertical tail is prohibitive for that plan.

I do have two 24v wheelchair motors and a 43 amp dual H bridge. The AirWheel has no problem lugging my 180 lbs / 81.64 Kg up hill at about 10 mph / 16 kph. I'm not a very good fabricator but with some PVC and duct tape and a glue gun, I'm unstoppable.

Cheers,

Bill

Since it is two wheels , you should be able to hack it so that when you need to turn left that it " skid steers" one wheel reverse and other forward to twist in that direction

Jstarns, The two wheels are inseperable. They're linked by a single rim.

I've decided to scrap this project because it seems too impractical as a robotic platform. A robotic arm would always have to be counter balanced. If used as a cart, adding and removing things would send it flying out of control without sophisticated controls.

I'll try one last thing suggested above of powering the servos independently of the EZ B. This will prevent the brown out issue and supply more power to the servos. The supply I'm using is the 12v 1A from the Ez Shop.

I'll post a video of those results.

Thanks so much and merry Christmas,

Bill...

I tried one of these airwheels once. If you don't mind me asking, how many times did you break your nose when it flipped?

I would suggest adding some sort of metal bars close to the floor. That way when it flips it doesn't break the robot.

have you tried using two separate arms, one for the front of the wheel and the other for the back? you might be able to achieve a better weight distribution that way.

Hey Sudo,

Only crashed once while looking sideways trying to read my rated speed in a digital sign. Scrached knee only.

Putting a servo arm on the side would make it move forward and backward more efficient but turning would could be more of a challenge. However opposing pendulum motions on each of these ends could make it twist. HHHHmmmm...

I followed Dave's suggestion and powered the servos independently of the EZb per this diagram below:

The servos were much more responsive and browned out less but it still seemd to draw too much current from the 12 v 1A power supply causing the Ezb to reset.

I'm going to scrap this idea for my laundry cart bot for a more practicle 6 wheel machine. It'll be two wheelchair motors in the center with 4 swivel wheels on the corners. I'm using a high tech looking full tower computer case for the base. I'll be posting updates on this thread: synthiam.com/Community/Questions/6788

Thanks so much for all your support.

You guys are awsome! Bill