Steering - is by moving CoG to one side of the contact patch. Easier said than done - as leaning to one side causes the hoop to tip in opposite direction - & you continue straight on! In 1687 a smart cookie worked all this out. Look up his "Laws of Motion":-
Braking - is done very gently. Only possible from speed - with the help of boots with tough sliders. A successful World Record requires Feet Up during the measured distance.
Gyroscopic Effects & Handling This (& position of GoG) is what makes a monowheel work. Some people find a sweet combination by judgement (or luck) - we found it by testing the boundaries on many 'bad' permutations - & established a combination that works for us. It's unlikely that we've found the optimum?
Rotating Energy - is generated by Mass, Dia & Speed of the hoop, but also by the engine & other rotating parts, which all result in gyro effects. When we started on Silver, we had a lightweight (plastic) hoop, engine behind the rider, engine contra-rotating (with drive on Outer surface of the hoop) - and suffered a force we called 'Magnetic Attraction' - a new Monowheel force that would suck us into every obstacle on the airfield (usually plastic rubbish bins). We could get ourselves rolling, but on attempting to Steer Away from a bin, the damned thing would Turn In - Towards that bin? It was a nightmare!
We spent 18m changing all sorts of things. Including reversing the direction of travel with new seat & handlebar arrangement (so the engine was ahead). We explored weight of the hoop, swapped to metal hoops, and finally built a different transmission arrangement. This had Internal friction drive - which made the engine co-rotate with the direction of travel. Each step made a significant improvement - which we can now explain:-
Co-Rotating engine - essential. Gyro precession (that curious effect as you twist a flywheel) generates a force on the axle at 90deg to the turn. This is Steering & Lean - a very natural effect. Except when motor is running in opposite direction, its gyro torque cancels the gyro stability of your hoop. We never got properly feet up until our engine was co-rotating.
Hoop Mass - we explored this effect of filling our light plastic hoop with different density material (plastic beads, water & sand). Initially, the only way we could get underway was with the heaviest version - but soon as we were moving (maybe 10mph) we found it took a serious physical effort to make it lean & steer. We reverted to the lighter fillings, and eventually a high tensile steel hoop (very thin wall, lowest mass we could achieve). When WarHorse was doing 60mph, a change hoop from 15kg to 12kg made a significant improvement in ability to hold direction (which involves a tiny bit of steering to keep yourself on course).
Steering under Acel & Decel - because CoG is ahead of contact patch (under power), leaning places that CoG in the direction you want to go - and the wheel follows. But when slowing, you've pitched forward - putting CoG behind the contact patch. This means that trying to turn while coasting or slowing - actually moves the CoG away from the direction you want - and the wheel tries to tip you off. This means:- When Slowing - a monowheel looses it's (limited) steering control. It's counter intuitive, but if drifting off course Do Not Throttle Back. Instead, Wind On just a little power. Then you can place the font where you want to go - and regroup for slowing (if you have the space?)
Additional Gyro - many people tell us to add one. We tried - and didn't get on with it. Think we understand the reason - but have never gone back to explore. Probably something we should revisit. Would love to hear your experience?
Rolling Resistance - this one is Simple. It must be as Low as Possible. Excess drag in the drive means changing between Acel & Decel exaggerates the change in torque reaction, which increases the pitch change for your throttle change. When pushing your wheel around, the stator part must hang at BDC (instead of rising up as the hoop rolls). This drag also absorbs power, which reduces speed, increases heat & wear in your transmission. We don't like these, as they reduce life of moving parts, which leads to mechanical failure. Worst case scenario - Seizure, or Derailing.
Freewheel - Cannot stress how important this is if you are designing for over 20mph. We added them when we started tuning an engine to 3x its rated Speed & Power (way over its design point). It was not a case of 'If it failed' - but 'When it failed', and we've had engine cuts & failures on all of our machines (brown trouser moments!). Freewheels have Saved our Lives.
30mph Speed Wobble - every rider we know (who's exceeded 30mph) has experienced this scary effect. We think it's the Natural Frequency of the Spring-Mass system for a typical Tense rider & monowheel, generally between 25mph & 30mph. It causes resonance, that you 'Fight' with all your Strength. For us it comes at a lower speed when slowing.
You will meet this, first time you attempt to build speed - and you're holding on for dear life. Try to relax & press on. In time, you will find yourself driving through to a very rare experience - the calm world of Rock Solid Lateral stability at Speed! The wheel can do nothing but continue in the direction its going. At this point, all your effort is on a Smooth Throttle, while maintaining Course (the wind is pushing you), while keeping Feet Up, while thinking "How am I going to Slow this thing Down?" (perhaps not so calm?) You have to pass thru that same resonance, this time with the loss of stability from position of CoG. The secret is to relax again. Go Limp as this reduces the spring rate of your body. Use your Sliders, to add damping to that resonance.
Some Good News - you don't need physics to get thru 'The Wobble'. If your wheel has reasonable stability- you will learn how to 'Work with It' (instead of Fighting It) - and the smile gets bigger.