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Topic: Challenge: horizontally / inertially stabilize a pizza on motorcycle (Read 3583 times) previous topic - next topic

Retroplayer

I guess I am also one of those people that doesn't believe that a microcontroller is the solution for everything. Add me in for the gimball. A well balanced, bearinged and weighted gimball will react a million times faster than any closed loop micro/motor/sensor could ever respond.

jroorda

I should really clarify my previous post.  When I said the a doubted a car could turn fast enough to harm a pizza I meant purely rotationaly.  Imagine a pizza rotated about the middle so that it spins around.  Now imagine how fast one would need to spin this pizza or how hard one would have to accelerate its rotation to do it any harm.  I would imagine that it would need to be quite fast, and while his driving is amazing the maximum rotation rate is likely not in excess of 180 degrees a second.  Not near enough by itself to harm a pizza.

The issue is the sideways g-force that is generated in the turn.  This defiantly would harm a lowly pizza, but this sideways force is something the accelerometers can sense and your platform can realign to be straight down relative to the pizza.  As far as the pizza is concerned gravity just got a bit stronger, but any sideways force is countered by the force of gravity which is no longer straight down on the pizza.

A well weighted suspended platform could work well and would be simpler, but without damping you could get oscillations at its resonant point that could harm the pizza too.  After any sudden stop you would get a swing-set effect.  Damping would help, but it would also slow the response to a sudden impulse.  Good gimbals with a pair of positional servos could likely react faster than a simple pendulum without any noticeable oscillation. I would bet your main sensing loop could run at least a few hundred times a second making the system very low latency.  The limit would be the maximum rotation rate of your servos, but they can be quick as well.  Without the motor the platform is essentially a proportional controller.  If you do a little looking into controls theory you will find why a proportional, integral, derivative controller (PID) would result in faster rise times with much less oscillation. 

Retroplayer

I think the biggest destructive force is that a motorcycle leans in turns. This would essentially lift the pizza up (assuming the box is affixed to the bike), which reduces the friction and the pizza will basically continue trying to stay in place while the box is moving. For most other movements of the bike, the friction of the pizza is likely enough to keep it moving along with the box. The little plastic spacer they put in the middle of the pizza would help a little with keeping the pizza from lifting.

PeterH

I think the biggest problem in the moped/pizza scenario is that as the moped goes over bumps the pizza will sometimes have little/no contact with the pizza box - any time this happens while the moped is accelerating/braking or being thrown around sideways, the pizza will tend to shift and end up crumpled against the side of the box. Probably the best thing you can do is give the pizza box relatively soft vertical suspension with plenty of travel, and tell the rider not to accelerate or brake hard.
I only provide help via the forum - please do not contact me for private consultancy.

Dnos

Your location information is missing from your forum profile. I can make recommendation to a simple accelerometer but the shipping will be expensive if you are not on my part of the world.
I'm in Berkeley, Calif.

Dnos


I think the biggest destructive force is that a motorcycle leans in turns. This would essentially lift the pizza up (assuming the box is affixed to the bike), which reduces the friction and the pizza will basically continue trying to stay in place while the box is moving. For most other movements of the bike, the friction of the pizza is likely enough to keep it moving along with the box. The little plastic spacer they put in the middle of the pizza would help a little with keeping the pizza from lifting.


THe pizzas will be in a box, which will be in those insulated delivery bags, which will be in a plastic luggage box, which will be connected to a luggage rack on the back of a bike.

If you guys haven't seen this, here's a thread about using accelerometers, gyros, kalman filter, etc. http://arduino.cc/forum/index.php?topic=58048.0

Retroplayer


Quote
THe pizzas will be in a box, which will be in those insulated delivery bags, which will be in a plastic luggage box, which will be connected to a luggage rack on the back of a bike.

We all love theory, but have you actually just tried it on the bike to see what would happen?
Maybe there's no problem.


Yep. I'm out. Seems like over-engineering for something done more simply another way. But, I can realize that there is fun in learning all sorts of new things attempting this, so no harm in doing it. I just tend to try to stick to the KISS principle and this forum heading did mention "advice on feasibility."

Good luck, OP. It does sound like fun.

Dnos

I just tend to try to stick to the KISS principle and this forum heading did mention "advice on feasibility."

Good luck, OP. It does sound like fun.


I dont expect everyone here to speak english as a first language, so I'll just say that "feasibility" does not mean "shoot someone's project down" and then "Argue about the best reason not to do something." It means "How possible is it for something to be done." Nobody has said anything about the "feasibility" of this project. They just recommended that I do it their way with bowls of paint, weights, or some other device not including an Arduino.

For the most part this discussion has been guessing what happens to a pizza on the back of a motorbike. I'm tired of posting about this and having nobody read them so I'll just say this: IT DOES NOT MATTER. Forget about the pizza for a second, just help me build a platform that remains horizontal while the bike is at tilt.  THAT's the goal. You can tell me how dumb you think the idea is later. For now I know that the hardware required is the exact same hardware that this uses:
http://www.instructables.com/id/ArduRoller-balance-bot/

There are many other iterations of this same design, so I know creating what I want to create is 100% feasible, and has been done by many other people. Only difference is that nobody has  stuck one to  a bicycle or motorcycle


I'll ask oric_dan to please only post if there is something constructive to add to the subject.

Retroplayer

#23
Feb 05, 2013, 02:14 pm Last Edit: Feb 05, 2013, 02:21 pm by Retroplayer Reason: 1
Quote
You can tell me how dumb you think the idea is later.


I, personally, never said your idea was 'dumb.' I don't think it is at all. I am just of the opinion that there are much simpler ways to accomplish your goal and you are stuck doing it the way you want. There is nothing wrong with that, but you are asking others to go down the hard road with you when they know there are simpler ways or that in the end, it really isn't as much of a problem as you present. It's that simple. If you want to be stubborn about HOW you do it, you should reasonably expect that you may have to go it alone. That's all. I do that all the time, myself, and usually have to go it alone.

My unsolicited advice is to post specific parts of your project asking for help separately as you encounter problems. When you put out the whole thing at once, you are inviting comments on how to solve the overall problem, when you really want to do it a very particular way. So, post those 'particular ways' spearately to get advice on how to implement them.

There is alot of value in doing things the hard way. That's the best way to learn. Getting butt-hurt on a forum is a sure-fire way to stop people from trying to help as you just come across as stubborn and argumentative when you do that.

Again, my unsolicited advice. Take it or leave it.

Good luck with your project.

To make this a constructive post, if you don't view it as one, try starting here: http://blog.makezine.com/2010/04/28/ball-balance-machine/

Dnos

I'm not interested in arguing with you so please stop. Take the attitude somewhere else.

There is no "hard road" for you. You either can contribute to the hardware parts list or you can't. And i havent been stubborn. Your idea of adding a swinging counterweight to the back of a bike has some issues. The added weight, the uncontrollable momentum, the added height and width required for the mechanical gimbal would be a lot. The idea of using an arduino is simple because its already been done many times in many different ways. By making this thread I hoped to reach out to one of those people.

PeterH

I assume you can make/find a pivoting assembly and actuators capable of positioning it as fast as you need. Figuring out what 'horizontal' means is going to be the tricky bit and will require clever combination of gyro and accelerometer input. Maybe you can 'borrow' the code for this from an existing balance bot, but I suspect you'll find that most of them just go from sensor input to negative feedback directly without ever explicitly calculating the orientation of the vehicle. You might find that the Arduplane project gives you a better starting point, and if you also take one of the purpose-built Arduino clones and use the 'gimbal control' feature you can probably get it to do what you want with relatively little effort.

Obligatory disclaimer: I don't believe the behaviour you're trying to achieve will give you any benefit in the pizza delivery stakes. :)
I only provide help via the forum - please do not contact me for private consultancy.

oric_dan

Quote
Getting butt-hurt on a forum is a sure-fire way to stop people from trying to help as you just come across as stubborn and argumentative when you do that.

Some people just don't understand what a **public** forum is all about. Also, given the
reactions, I doubt pizza has anything to do with this, it sounds more like a senior project
assignment.

Dnos

Peter, the software can always be tweaked later. I'm right now unable to get to that point because I don't know what parts i need. There are many arduinos, shields, accelerometers, gyros, motor controllers to choose from. I wasnt thinking actuators, just one stepper motor. Ill look into it.
For purposes of simplicity I think I'll start by building this, then work on scaling it up http://revenanteagle.org/checksix/gyrocam

Oric, a public forum means anyone with an Internet connection can say and do whatever they want, act as an authority, or as a troll, with pure anonymity. I'm not sure why you're so proud of that. This is an arduino forum. One who posts on an arduino forum would expect help with arduinos. Not a bunch of people saying dont bother.

PeterH

If you research the Arduplane project you'll see they have some Arduino clones with integrated gyros and accelerometers, and open-source software to deal with the sensors and figure out what's happening. I understand that one of the options on this project supports a 'gymbal' mode which is designed to keep a camera mount on the drove at a constant orientation as the drone itself tilts and turns. That sounds very similar to what you're trying to achieve and I think it could form the basis of your sensing and control algorithm.

You still have to design your own hardware and decide what sort of actuators you're going to use. Perhaps you could find some really beefy model servos that would do the job, but that part's up to you. How you power and drive the actuator depends on what actuator you select. Perhaps you would consider making a small mockup using plain ordinary model RC servos to prove the concept, before you try to scale up to something suitable for your full solution.
I only provide help via the forum - please do not contact me for private consultancy.

oric_dan

Quote
One who posts on an arduino forum would expect help with arduinos. Not a bunch of people saying dont bother.

You really misinterpreted this entire thing. The problem was presented as a systems-level
problem, and most of the posts here were from people looking at it from that perspective.
There are at least 20 or 30 or more aspects involved in the first post on this thread.

You can't solve that kind of problem without taking a multi-faceted approach, and people
responding in the "Project Guidance" section generally understand that, so that's how they
approach solutions. Consider all the aspects, and different approaches, from the get-go.
There are 'many' aspects to a problem like this that may not be obvious at first glance.
They all have to be sorted out.

If all you had wanted was a p/n for a gyro or accelerometer, or which value resistor to use
in a ckt, then that would have been something other than how the so-called "Challenge"
was presented.

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