# Going round in circles with Ackerman

Got up at 6:30 AM to take the dog to day care. Went back to bed after not sleeping at all. So didn’t really start until gone 11. Got straight into it though. Still all physics related. Today I had to do something with Ackerman. Basically if you have a vehicle with turning wheels you want the outer wheel to turn at a shallower angle than the inner wheel. The question being, what is the angle? Well ok, if you take the steering angle to be the left wheel, so you are turning left. If the neutral steering position is at 0 then turning the wheel left will give you a negative angle. What you need to do is work out the intersection point of the wheel normal to the line of the rear axle. Which sounds more complicated than it actually is. Using basic trig, the angle at the wheel is half pi minus the wheel angle, so at 0 it will never intersect, then as it turns the opposite line length will get less. So using the tangent you know the wheel base and now the angle, so can work out the distance along the axle line. Now you know this, you have the centre point of the imaginary centre circle. If you then add on the axle width you have the adjacent, the opposite is just the wheel base. Using the arc tangent you can now work out the angle require to the right wheel. So what you are doing is producing two circles, one the inner wheel follows and the other the outer wheel follows, the object being that you then get less wheel scrub. This is called Ackerman steering.

Had another lot of cleaners turn up. They apparently got lost in Fishponds. I picked the dog up. Came back and did more physics stuff.

Did another Japanese lesson, still going well.

Had a bath as still feeling a little bit shit. Planning on drinking lots so I stand the chance of sleeping.