Self-Balancing Bot w/ 12V Parallax Wheels (attempt)
Got the motor mount and wheel kit from Parallax when saw it was half off:
https://www.parallax.com/product/motor-mount-wheel-kit-aluminum/
Also, got a caster to make a 3-wheel bot.
But, then saw a bunch of self-balancing bots and decided to try that first.
Here's the concept (see attached pic).
The construction is 1/2" HDPE and 1/4-20 hardware.
Just CNC'd the main board and it seems pretty solid, even with the giant hole in the middle for the battery.
How high up or how low to mount battery is perhaps the main question. Or, maybe if this battery is too big is another... Been reading that being top heavy is actually an advantage for self-balancing bots. But, think this SLA battery is beyond the pale, so lowering it via the giant hole. May try different amounts of lowering if this doesn't work.
Plan is to use P2 and BNO086 sensor in RVC mode to achieve balancing.
Might be a disaster, we'll see!
Comments
Hi,
"Steiner's theorem" https://en.wikipedia.org/wiki/Parallel_axis_theorem gives that the moment of inertia grows with the height in a quadratic way. As the moment of the weight corresponding to the deviation of a certain angle only grows linearly, it will be much more easy to balance, when you battery is mounted high. It is funny, that the long long rocket is a shape that is far more easy to balance than your shape. So if you succeed, the rocket will be easy-peasy for you next....
Christof
Hanno Sanders used cascaded PID
@Mickster I remember Hanno's bot from years ago...
Got the wheels assembled.
After looking at Arlo, thinking might be better to have motors on top. Mostly because of wiring...
The allowable rotation angle goes down a hair, but not much.
Ground clearance also about the same.
Pretty sure that bot is going to need to balanced to start out with. Need to add weight to the front...
That's the sort of thing that can be handled by an offset...added to the PID output. Same applies with vertical axes to compensate for gravity. I wouldn't needlessly increase the inertia...JMO
Think you can do an offset but then the platform wouldn't be level when balanced.
Funny that nobody seems to mention that anywhere, but pretty sure it's true.
Also read about needing to fuse in data from the accelerometer because rotation angle can drift over time.
Not seeing that with BNO086 in RVC mode though...
Seems rock solid.
BNO086 also seems to know about its absolute angular position, which is interesting.
It must be doing some kind of calibration at start up to figure that out.
Also read that one needs 300 RPM motors and enough torque.
These motors are rated at 95 RPM.
Thought that might be a problem for a second, but now thinking that the 300 RPM is for tiny robots.
This one is very massive and don't think it needs to move that fast.
Found an example on the web of a similar bot that worked.
Wasn't quite as massive as this one though, so think it good shape.
PID is wonderful. It can take care of everything. The offset can be adaptive.
One of the problems that I see with these hobby devices is low resolution feedback. You can't have too much.
I like those CUI modular encoders and 4096 line are available. This translates to 16384 quad counts/rev and we have Prop horsepower.
Oh heck, we are talking about servo motors, right, not steppers?
I not familiar with the product 😊
It’s just the parallax dc brushed motors from the Arlo bot
Going to use with parallax pwm MOSFET hbridge driver board
Hi, how did you model this? It would be great, if we could switch to FreeCad for all the mechanical designs. As we now see the version 1.0 https://freecad.org/index.php?lang=en
@ErNa FreeCad does look nice. Used SolidWorks for this because that's what we use at work...
That reminds me, I have to come up with an explanation why this is needed at work...
Main HDPE board was bowing a bit, so added a piece of t-track that was around.
Seems better now...
Liking the wheel supports. They certainly didn't cheap-out on this.