Calling bike physics/tech experts!

**bogan** · 16th April 2010, 16:45

Originally Posted by DangerousBastard

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.

steppers are generally used for non-feedback high precision position control (my guess is thats what the above guy uses), so having a bump upset the step count would remove that benefit though you could do as you say with a standard DC motor to measure current/torque just as well. Ill add that to the list of things to look into more:
Voice coil
DC motor
Pnuematics
is what I've got so far.
Yeh the XYZ sensor (I assume that means accelerometer) would be a plan for sensing lean angles, dunno if you remember the traction feedback device thread from bout a year ago? it went over a lot of that side of it.

Originally Posted by 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.

The steering on this is accomplished by changing the angle of the forks, not the turning of the forks. Are the newer ones like that?
Exactly. The "steering" action is actually free, for some small angle (about 15 degrees either side). When you steer the bike, the steering leans to the desired side, and then the chassis follows, leaning to the same side. Stability is produced with the spin of the front wheel, which acts as a flywheel, with the metal inside the front tire.

sounds like rc bikes use different steering technology to full size bikes, which doesn't sound at all transferable.

**paturoa** · 16th April 2010, 17:04

I think you'd need a (twin contra rotating?) gyro measured system too to determine lean and turning.

Would the damping ratio and pressure change with speed as the gyro effect of the front wheel increases?

I agree with the pressure not displacement, as to initiate the turn "counter steering" pressure is required, but the displacement is positive. Interesting control problem, as after the turn starts the pressure would increase as the bars turn the opposite way to the pressure as the turn commences.

Interesting to think this one through!

**bogan** · 16th April 2010, 17:11

Originally Posted by paturoa

I think you'd need a (twin contra rotating?) gyro measured system too to determine lean and turning.

Would the damping ratio and pressure change with speed as the gyro effect of the front wheel increases?

I agree with the pressure not displacement, as to initiate the turn "counter steering" pressure is required, but the displacement is positive. Interesting control problem, as after the turn starts the pressure would increase as the bars turn the opposite way to the pressure as the turn commences.

Interesting to think this one through!

Um, contra-rotating gyro would have no net gyro forces wouldn't it?

Pressures etc would increase with more speed, will have a lot of monitoring equipment on the bike so will be easy enough to factor in that increase, or program it to learn itself.

**gatch** · 16th April 2010, 17:16

How about a rail gun instead..

**bogan** · 16th April 2010, 18:08

Originally Posted by gatch

How about a rail gun instead..

nah, flatmate called dibs on that idea

**Ocean1** · 16th April 2010, 18:16

Originally Posted by bogan

Um, contra-rotating gyro would have no net gyro forces wouldn't it?

Don't believe so, google gyro platforms, (the physical frame for a gyroscopic compass).

In fact a gyro platform is likely the best way to establish a baseline for the bike control, some good examples in sports photographic systems... like this: http://www.aerialexposures.com/review.htm

**bogan** · 16th April 2010, 18:24

Originally Posted by Ocean1

Don't believe so, google gyro platforms, (the physical frame for a gyroscopic compass).

In fact a gyro platform is likely the best way to establish a baseline for the bike control, some good examples in sports photographic systems... like this: http://www.aerialexposures.com/review.htm

I was under the impression contra-rotating was two objects rotating on the same axis but in opposite directions, so the gyroscopic precessions would cancel out.

How would I use a gyro platform (one in you link has 3 gyros in it i'm guessing?) to establish a baseline? Do you mean use it as a gyro based tilt sensor?

**Ocean1** · 16th April 2010, 18:45

Originally Posted by bogan

I was under the impression contra-rotating was two objects rotating on the same axis but in opposite directions, so the gyroscopic precessions would cancel out.

It's all mass and it's all rotating, gyro platforms usually have two or more flywheels. Military platforms for weapons guidance are the top end, they spin up huge revs in order to keep the mass low.

Originally Posted by bogan

How would I use a gyro platform (one in you link has 3 gyros in it i'm guessing?) to establish a baseline? Do you mean use it as a gyro based tilt sensor?

Yes, connect X and Y axis transducers to the platform and feed the outputs to a PLC. The PLC controls the steering based on whatever parameters experimentation shows works. The programme could get a bit complex, and fairly counter-intuitive…

**grusomhat** · 16th April 2010, 18:46

Interesting thread. Keep the tech talk coming!

**bogan** · 16th April 2010, 18:54

Originally Posted by Ocean1

It's all mass and it's all rotating, gyro platforms usually have two or more flywheels. Military platforms for weapons guidance are the top end, they spin up huge revs in order to keep the mass low.

yeh but I'm pretty sure they will never be contra-rotating, in fact flywheel energy storage systems used in cars use contra-rotating discs so the gyroscopic effects are canceled out. Its also why motogp bikes (i think they do this now, or it could have just been an idea) have the crank turning the opposite way as the wheels.

Originally Posted by Ocean1

Yes, connect X and Y axis transducers to the platform and feed the outputs to a PLC. The PLC controls the steering based on whatever parameters experimentation shows works. The programme could get a bit complex, and fairly counter-intuitive…

Yeh I won't be using a PLC, computers are so cheap and they run C# (FTW), but was considering using a gyro tilt sensor, would get away with a single disc one as bikes heading is irrelevant at this stage. Could get massive precision out of it using air bearings for the frame and 4096 position magnetic encoders.

**CookMySock** · 16th April 2010, 19:18

Originally Posted by bogan

steppers are generally used for non-feedback high precision position control (my guess is thats what the above guy uses), so having a bump upset the step count would remove that benefit though you could do as you say with a standard DC motor to measure current/torque just as well. Ill add that to the list of things to look into more:
Voice coil
DC motor
Pnuematics
is what I've got so far.
Yeh the XYZ sensor (I assume that means accelerometer) would be a plan for sensing lean angles, dunno if you remember the traction feedback device thread from bout a year ago? it went over a lot of that side of it.

I'm a bit pissed, but steppers can do a lot more than position things with some processor behind them. Yes you will have to think in advance what will happen - theres no way you will be able to just fire some step commands at a corner, but I think in the end there is a lot more that can be accomplished.

You will have to hydraulic-damp any pneumatics or other force-based systems or bumps are going to be hell. Maybe at high speed it will be smooth, but at low speed it will flop around like a bitch.

With displacement servos you will need to measure steering system torque and follow the front wheel around with the stepper to set torque to the desired amount. So the steering input will be that torque you measured rather than the steering input you created. Clear as mud? So you don't talk to the stepper directly - the torque feedback loop does, and you just input what steering torque you want and the stepper ramps it up.

Steve

**Grasshopperus** · 16th April 2010, 19:28

I'd be keen to help out, obviously we'd need to set this up on a gsxr-1000 and make it do a lap of pukekohe or something.

I think you could avoid using a stepper motor by using a pulley system with to control the steering with a gyro and Ping-type sensors on either side of the body to figure out lean angle. It would work similar to the typical 'balancing bot' project that you see guys doing as basic microcontroller programming projects.

Then you could get hardout with a forward-facing laser scanner to map upcoming contours and such to anticipate bumps and dips or just make sure it doesn't run into anything.

It's not just the alcomohol talking, I'm keen.

**Ocean1** · 16th April 2010, 19:36

Originally Posted by bogan

yeh but I'm pretty sure they will never be contra-rotating, in fact flywheel energy storage systems used in cars use contra-rotating discs so the gyroscopic effects are canceled out. Its also why motogp bikes (i think they do this now, or it could have just been an idea) have the crank turning the opposite way as the wheels.

They do use contra-rotating flywheels. I’d say the aim is to eliminate precession issues (the 90deg deviation to external inputs) but retain the stability function.

Originally Posted by bogan

Yeh I won't be using a PLC, computers are so cheap and they run C# (FTW), but was considering using a gyro tilt sensor, would get away with a single disc one as bikes heading is irrelevant at this stage. Could get massive precision out of it using air bearings for the frame and 4096 position magnetic encoders.

A gyro is the easiest way to get attitude data, an accelerometer won’t work. Yup, get an old laptop for a donor. In fact you could build a tolerably good gyro from the hard drive…

Be much easier if you don’t mind recycling existing systems. Go see New Age Materials on Gracefield Rd and rummage through their stuff. Or Casa Modular Systems in Petone.