Calling bike physics/tech experts!

[bogan]

So I'm nearing completion of my electric bike project (electric bucket hopefully) so starting floating ideas for the next big project. Been thinking bout doing an autonomous bike project. Something like this



but better with a bit of luck

First step will be to adapt my learner bike (VT250) for remote control use. I reckon clutch, throttle, brake, will be easy enough (from theoretical perspective) to sort but steering will somewhat more difficult. It appears that the above guy uses a motor and encoder to steer, which appears to give a rather jerky steering system. I have different ideas, but would like to hear what you guys reckon first?

[Headbanger]

I have different ideas, but would like to hear what you guys reckon first?

I reckon you're a bit mad

[munster]

Looks interesting. Keen to know more about your electric bucket racer. I've been thinking about something similar for awhile. What sort of motor did you use (voltage, amps etc) and power controller?

[Urano]

i'm on an "almost" electric project too...
pretty interested in that, but maybe we're a bit out of topic.
i'd really like to keep in touch about that, anyway...

[Jonathan]

I reckon you can get inspiration from the fat armless Chinese guy.



All you need is a weight in the centre of the bike that leans to the left and right and is connected to the bars just as Mr Yeung there. He doesn't need to push, doesn't need to pull, just leans from side to side.

Guess it is just the same concept as above though...

[bogan]

To those enquiring about the electric, I'll put up a thread once thats done, hopefully it'll turn into a big one so all that have enquired will notice it.

Interesting thought Jonathan, though is the shifting weight important? as steering will shift the CM to start/adjust a turn anyway.

[CookMySock]

The problem with pushing on bars is, the push has to be a pressure not a displacement, so the task is either to engineer the servo to be a force system and then figure out the damping (the hard way IMO), or else use a displacement servo and get some torque feedback and do it all in software.

Steve

[bogan]

The problem with pushing on bars is, the push has to be a pressure not a displacement, so the task is either to engineer the servo to be a force system and then figure out the damping (the hard way IMO), or else use a displacement servo and get some torque feedback and do it all in software.

Steve

Exactly what I thought, however theres a third option, use a voice-coil actuator and position encoder

[R-Soul]

The problem with pushing on bars is, the push has to be a pressure not a displacement, so the task is either to engineer the servo to be a force system and then figure out the damping (the hard way IMO), or else use a displacement servo and get some torque feedback and do it all in software.

Steve

Why do you say it must be a pressure and not a displacement. (and I stand corrected on this but )If you are putting pressure on the bars, but not getting any displacement out of it, you are not going to be making a difference to the steering geometry or lean angle, and hence no difference to the steering itself?

[R-Soul]

How about a four wheeled bike like the 4by or the Yamaha prototype bike?

[bogan]

Why do you say it must be a pressure and not a displacement. (and I stand corrected on this but )If you are putting pressure on the bars, but not getting any displacement out of it, you are not going to be making a difference to the steering geometry or lean angle, and hence no difference to the steering itself?

think what he means (and what I mean), is control the pressure, not the displacement, most motors control displacement rather than pressure. The reason is to allow the bars to move about a little bit with bumps etc, and to avoid big forces that would be involved with a displacement based system.

How about a four wheeled bike like the 4by or the Yamaha prototype bike?

[CookMySock]

Exactly what I thought, however theres a third option, use a voice-coil actuator and position encoder

Yes that would be your 'force' rather than displacement servo, but that operates undamped, and now your software has an enormous task ahead of it figuring out what the fuck just happened after the littlest surface irregularity. It may be that you could use a variable steering damper and help it a little, but I think you will find the bars will just fling everywhere out of control.

The difference between force and displacement on a gyro is simple maths, so if you used a stepper motor with transmission, frame x,y,z sensor, measure bar torque (motor current?), I think you could easily calculate what was going to happen. The system would be naturally damped and the stepper could possibly even permit movement from an external shock to the steering if you chose to.

Interesting!

Steve

[Hoon]

RC bikes use a servo to control their steering so I can't see why that wouldn't work if scaled up. The servo steering horn would need to utilize some sort of spring/damping system to absorb bumps. I would leave the actual bump handling to the main sensor/steering feedback loop.
In fact I'd start off first with a 1:5 radio controlled bike, get my sensor/software/control side of things sorted first then scale up to a full version as testing could become a bit of a concern with an unpiloted motorcycle.

[bogan]

Yes that would be your 'force' rather than displacement servo, but that operates undamped, and now your software has an enormous task ahead of it figuring out what the fuck just happened after the littlest surface irregularity. It may be that you could use a variable steering damper and help it a little, but I think you will find the bars will just fling everywhere out of control.

The difference between force and displacement on a gyro is simple maths, so if you used a stepper motor with transmission, frame x,y,z sensor, measure bar torque (motor current?), I think you could easily calculate what was going to happen. The system would be naturally damped and the stepper could possibly even permit movement from an external shock to the steering if you chose to.

Interesting!

Steve

hmmm, think there is still some damping in a voice coil, as wires moving through magnetic feild, so could possibly control damping using the driver circuitry, will have to look into how much could be provided though. Also as the 'bars' are moved the encoder would pick that up and the force could be adjusted to compensate, or I could add a steering damper!

ah fuck, gtg, will look at ur second point later

[Maki]

Why do you say it must be a pressure and not a displacement. (and I stand corrected on this but )If you are putting pressure on the bars, but not getting any displacement out of it, you are not going to be making a difference to the steering geometry or lean angle, and hence no difference to the steering itself?

"I am a master of physics, I agree with dangerousbastard, no point in repeating what he said."