Lately I've been fiddling round with a new spreadsheet sent to me by Peter Eland that we can use to measure exactly what Ackerman angle we should have on the track arm of our trikes.
Do you know what Ackerman is? Simply it's the angle of the track arm set so the wheels don't scrub in a turn.
It isn't real clear how to use the spreadsheet if one hasn't had much to do with Excel but now I've figured it out it's pretty good and helpful for my machines. There are only 4 necessary numbers to gather.
Fill out these numbers replacing what is there for:
a - this is the distance from the centre of the trike (EG boom) to where the axle goes through the kingpin. When asked exactly where do you take the measurement point on the kingpin Peter replied 'Anybody's guess really - that's the trouble with modelling a 3D system in 2D. I would favour the intersection of the axle and kingpin axes - i.e. bottom red arrow in this pic with the axle on the bottom of the kingpin and top arrow in this one with the axle above the kingpin.
b - Track arm length from where the rose joint is mounted to the centre of the kingpin in a horizontal plane along the track arm.
C1 - angle of the track arm to the cross member. Hold a protractor and it's a bit of a guess but still close enough I recon.
i - wheelbase - measure from back wheel axle to the cross member but as the kingpins are sloped forwards to give castor you measure a bit forward of the crossmember to where the axles line up.
Now go over to the area on the right that says ideal Ackerman. The figures on the left show the turning radius of the trike and this is the turning circle the back wheel makes in the turn. I put the trike in the gutter out on the road and see how small a circle the back wheel will go round in. On the spreadsheet I use the number that closest resembles the best turning circle of the trike. You can choose new values yourself simply by typing over the values in that column.
Go across the line and it shows the error of the present setup you have with that tuning radius. To get the best angle of the track arm then go and adjust the C1 number till the error percent reads 0 for the best turning circle you have.
Hope this is clear. You may notice there isn't an ideal Ackerman then, it depends on how sharp a turn you want to do but it looks like if you get close enough to what you turn normally it's good enough.