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Balancing scooter project


#1

So, I have been thinking about doing a balancing scooter/robot project for a while now, and I thought I’d post here to see if anyone has any experience with these things.

At least for right now, I don’t want to carry people, but I do want something that can carry somewhere around 10-15lbs, since I figure that’s a good weight for my laptop as well as some other stuff.

Questions:

  • What motors to use? I’d like to stay as far away from brushed motors as I possibly can, and I’m not really sure stepper motors will work for this. If I use a hobby brushless setup, I need to then worry about cogging at low speeds. That sortof leaves my last choice as a hobby RC car sensored brushless setup.

  • What wheels to use? I’d kinda like it to be a bit rugged, be able to go over grass and such.

  • Weight distribution? It seems like I have seen two ideals on this, one where there is a lot of weight at the top of scooter and one where there is a lot of weight at the bottom. Any input on this?

As for the base, I was just gonna made a flat platform out of PVC and mount the motors on that. I’d like to avoid gear/chain drivetrains as much as possible. as I have limited MechE resources (though I do have a CNC and full workshop occasionally provided by a friend), I’d like to keep the mechanical part of this as simple as possible.

The control theory part is easy, no questions about that at all.


#2

The first one is probably closest to what you need. Not sure why so $$ there. You can build to match if you can find cheaper. Pololu does not sell brushless (except steppers) motors at all because of the bad control at low speed and the stop/starts.


Just something cool.
http://web.mit.edu/first/scooter/


#3

Arrrrggh, brushed motors. Hate 'em.

I wonder how fine of control sensored brushless motors allow for…


#4

Chris, You can put sensors to regular brushless rc motor by yourself. There is a topic on endless sphere: http://endless-sphere.com/forums/viewtopic.php?f=30&t=15686

Since it’s 3 sensors and usualy it is 14 magnets in motor I suppose you get 3*14 = 42 commutations per motor revoliution.

Sensors also solves starting problems at low speed.


#5

So Chris, why the dislike of brushed motors? They are simple and work fine for many applications. No need to over complicate things.


#6

I absolutely hate DC brushed motors because of how much noise they/their controllers introduce into the current source part of the circuit.

If you put a DC brushed motor/controller on an application that sources current from a single point like a battery, you end up with all sorts of issues with noise leeching into the power for the controller board, unless you put filters in/a good SMPS.

In the past, I have had brushed motors that have generated so much noise that they have reset uC’s on the same current source circuit (albeit, behind separate voltage regs).

As for Rimvis, thanks for that link. I actually saw that video on Youtube, but I couldn’t find any details behind it. I might just do that then…


#7

[quote]If you put a DC brushed motor/controller on an application that sources current from a single point like a battery, you end up with all sorts of issues with noise leeching into the power for the controller board, unless you put filters in/a good SMPS.

In the past, I have had brushed motors that have generated so much noise that they have reset uC’s on the same current source circuit (albeit, behind separate voltage regs).
[/quote]

That is in no way unique to brushed motors. A good quality speed control on a brushed motor won’t produce any more noise than a brushless motor, induction motor, etc, etc. In fact a Variable Frequency Drive for a three phase motor is one the ‘noisiest’ there is.

I suspect that since brushed motors are cheap and have been around much longer there are a lot more ‘cheap’ brushed motor controllers available.

My point is don’t discount a brushed motor unless another technology offers a clear advantage in performance. All of engineering is about a price/performance tradeoff. Spending less on motors may let you get a better controller and have as good or better system for less money.


#8

Hey Jeff. I need to the see the larger version of that avatar pic :slight_smile:


#9

LOL. Looks like young Master Yoda. :slight_smile: