escooter diy steering geometry problem

ors150

100 mW
Joined
Jan 7, 2018
Messages
49
Hello friends,
After building my own diy escooter ( it's amazing) ,
I'm having some problems with steering inputs ,
It feels like when ever I try to move left or right with the steering the scooter is really become unstable ( more speed more unstable steering)
I feel it's something with the geometry I have build for the steering,
I have tried to find some information about it but couldn't successed,
U maybe have any suggestions to what I should change in my front end?
Thanks alot
 

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SlowCo said:
IMG_20220208_174218.jpg

Your "rake" (steering/head tube angle) seems very "slack/lazy" and the trail very large.



motorcycle-rake-trail-offset-e1295912863770.png

ty alot for the answer,
so what should i change? ( i can change everthing if needed.) length the lower swing arm? or i should change also rake?
 
If there's any free play in the suspension pivots, also address that.
 
Chalo said:
If there's any free play in the suspension pivots, also address that.

nothing have freeplay, i really think its only a geometry problem that i need to understand more about it to start change something.
 
SlowCo said:
IMG_20220208_174218.jpg

Your "rake" (steering/head tube angle) seems very "slack/lazy" and the trail very large.



motorcycle-rake-trail-offset-e1295912863770.png

hey SlowCo ,
thanks for the reply , i have made an example of where my wheel bolt should be of course i will measure the trail and try to get it close as possible to 55mm to 75mm.
is it seems ok?
 

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I think the rake is not steep enough. More chopper than sportsbike.
So make the head tube angle sharper and rotate the (black) suspension downtube right under the head tube so it's parallel again. That will make the trail shorter also.
 
SlowCo said:
I think the rake is not steep enough. More chopper than sportsbike.
So make the head tube angle sharper and rotate the (black) suspension downtube right under the head tube so it's parallel again. That will make the trail shorter also.

Can you please send me a draw? I don't want to make mistakes again
Thanks alot
 
InkedTrail_LI.jpg


Steepen the head tube (search for photos of high speed scooters and try to replicate the head tube angle).
Then you'll need to re-weld the black front fork down tube so it is parallel again and won't hit the upward box section (green with holes). After that you can measure the trail and reposition the pivot point (bolt hole) of the front fork to get in the desired ball park. You might need to move the shock mount on the fork forwards to keep the suspension working correctly.
 
SlowCo said:
InkedTrail_LI.jpg


Steepen the head tube (search for photos of high speed scooters and try to replicate the head tube angle).
Then you'll need to re-weld the black front fork down tube so it is parallel again and won't hit the upward box section (green with holes). After that you can measure the trail and reposition the pivot point (bolt hole) of the front fork to get in the desired ball park. You might need to move the shock mount on the fork forwards to keep the suspension working correctly.

I see what u going for , u think that length the lower swing arm wont solve the issue?
 
SlowCo said:
It could make it better by only lengthening the fork. That is the least amount of work. So maybe try that first.

ok i will try i think to length the fork by 4 to 5 cm , i will look at it tonight
 
SlowCo said:
It could make it better by only lengthening the fork. That is the least amount of work. So maybe try that first.

ok i have an update , i have make the fork longer and now its on the right spot for the trail and feeling better steering but i dont like the look of it,
seems like a "chooper" like u said i think really the only solution is to cut the fork tube and remount it steeper and realign everything... alot of work but i dont wont to compromise
*the red mark is where the bolt of the wheel used to be*
 

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Yes, I think making the head tube angle steeper is the best way to go. A lot of work because all the other corrections you'll have to make. But it will give the best result overall.

If you look at high speed scooters the rake isn't even that much steeper and the trail is on the longer side:

Dualtron ultra.png
 
SlowCo said:
Yes, I think making the head tube angle steeper is the best way to go. A lot of work because all the other corrections you'll have to make. But it will give the best result overall.

If you look at high speed scooters the rake isn't even that much steeper and the trail is on the longer side:

Dualtron ultra.png

What you think is the angel on the head tube?
 
af0b6c1e2a25ba80286043df36374b82a5923dbf-1000x667.jpg


Autoped 1915
 
Hey guys i have found a video that explains about the trail very good , if any one is interested
there is a link:
https://www.youtube.com/watch?v=oXuq05tEk-Q&ab_channel=ZeroOneRacing

https://www.youtube.com/watch?v=Nmz1QJTDzO8&ab_channel=MikeonBikes
 
you need to get as much ground trail as possible. This swingarm design have a bult-in lack of rigidity compared to traditional bike suspensions, thus you need to compensate with more trail.

If it may help, I have approx 75deg head tube angle and 75-80mm trail on my scooter - Very stable up to 90Km/h

https://ibb.co/2F7YyYC
 
Fair bit of fettling needed to get that all singing together inline soon as one angles changed the fork will strike the frame on compresion so the hole front end may need a rework to get it handling nice no fowling.

Main thing is you now have spotted the error and understand the issue so a fix can be done, dont be hasty be sure 2nd time rite, your not the only one fella ive had my fair share of not to plan long as we learn from them we grow, keep us updated on your fix.
 
Some update:
Change the stem angle to 75, and fix the fork and weld everything now just need to grind and recheck the welds and asselm for test :)
 

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Update:
Fit all and painted all the parts that have been changed , but now there is a new problem at high speed I get steering wobbles "head snake" Any idea how can I fix it?
 

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Can you experiment with the pressure/length of the front and rear schocks to set put it more and less "on its nose". That way you can feel if that influences the tendency to wobble.
 
SlowCo said:
Can you experiment with the pressure/length of the front and rear schocks to set put it more and less "on its nose". That way you can feel if that influences the tendency to wobble.

i will try,should i add an damper?
 
If everything is tight (no play or flex and good torsional stiffness) and steering geometry is spot on you shouldn't need a steering damper. Also try to lean forward or backwards at speed to see what shifting of the center of gravity does to the wobbling.
 
SlowCo said:
Yes, I think making the head tube angle steeper is the best way to go. A lot of work because all the other corrections you'll have to make. But it will give the best result overall.

If you look at high speed scooters the rake isn't even that much steeper and the trail is on the longer side:

Dualtron ultra.png

HEY slowco after some ridding i think i should resovlve the issue,
i looked on the dultra is it ok that the meet point is above? the axle? becouse when ever i see trail and rake on photos the meet point as below the axle of the wheel,
at my scooter i have tried really hard to keep the meet point below the axle,
what u think?
thanks
 

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