LegoCube Posted August 21, 2015 Posted August 21, 2015 Hi, I searched the forum and found a few Ackermann questions already but they seemed old and somehow different enough to allow me to create my first own thread. I think I will also update the thread when my MOC moves forward. My main question at this moment is about an efficient way of setting up a Servo Motor to be used with Sariel's Ackermann steering as seen below: My version is slightly modified but the issue is same. In the picture there are the grey knoblike gears to control the steering. When setting up two of these gears like in the picture the axle seen at the top of the picture ends up at diagonal angle when the wheels are pointing forward. But with servo engine you need to have the the axle aligned to get centered steering. How to make this 45 degrees fix to align a servo motor to this steering system? I hope this makes sense, I still struggle with the terms used with Technic Legos. Right now I have removed the knob gears completely and attached the Servo Motor directly to the steering system vertically... But to achieve more low profile for the final build I would prefer the Servo Motor aligned horizontally. I am using SBrick to run L-Motor and Servo and some lights. Quote
Victor Imaginator Posted August 21, 2015 Posted August 21, 2015 You can always add pair of gears between this 45 degrees axle and servo Quote
LegoCube Posted August 21, 2015 Author Posted August 21, 2015 Thanks Victor for the answer. I now realize I need to get a 2:1 ratio anyway from Servo's 180 degrees to the car's 90 degrees. I hope this solves my issue. Quote
LegoCube Posted August 21, 2015 Author Posted August 21, 2015 I shortened the link and dropped the original gears completely. The axle is still not 100% aligned but getting there. Any thoughts of exact gear setup to achieve this? Direction of steering does not matter I van reverse it in SBrick :) Here is a picture of my quick test: http://u.cubeupload.com/Cu3e/fd6image.jpg Quote
MaxSupercars Posted August 21, 2015 Posted August 21, 2015 (edited) With this combination of gears you can not align the steering because of the same position of teeth on the gears circumference at 90 degree positions. You can use gear rack... Max... Edited August 21, 2015 by MaxSupercars Quote
Victor Imaginator Posted August 21, 2015 Posted August 21, 2015 Hmmm... LegoCube, you can try to achieve perfect angles with worm gear and horizontal placing of servo. But with additional gear reductions there will be too much backlash. And another weird idea - using chain with odd number of links will rotate one gear at half of the tooth. Quote
LegoCube Posted August 21, 2015 Author Posted August 21, 2015 (edited) Thanks for the comments! Moving bricks aside and gonna study about gear rack. That chain idea sounds awesome :) certainly trying it later. Update, i replaced the gears with thinner differential gears and inverted the servo inside the system. It looks awesome and compact :) Keeping eye on SBrick forum if I can find a software fix for the centering issue... Servo values are in magnitudes of 5 degrees? Maybe there is a way to make the controller fake incorrect center value. Also from my kindle version of Sariel's exellent book I noticed a freak gear with 14 teeth instead of the usual magnitudes if 4... Have to bricklink that to my small collection :) Later, thanks again! Edit: worm gear... That might be just the answer! Edited August 21, 2015 by LegoCube Quote
lcvisser Posted August 21, 2015 Posted August 21, 2015 Also from my kindle version of Sariel's exellent book I noticed a freak gear with 14 teeth instead of the usual magnitudes if 4... Have to bricklink that to my small collection :) Those are the old bevel gears. 2LegoOrNot2Lego uses them in his trucks, as you can see in the photos of a build here, for exactly this reason: they're not radially symmetric, which allows you to align them at 90 degrees. They're a bit weak though, but for just steering it should be sufficient if you brace them properly. Quote
LegoCube Posted August 21, 2015 Author Posted August 21, 2015 (edited) Thanks Ludo, I believe you mean this: Good to know it can really fix this issue. I also found that SBrick indeed has some values to play with this stuff. Edit: Removed misleading info/picture. Working SBrick settings few posts below Edited August 24, 2015 by LegoCube Quote
MaxSupercars Posted August 21, 2015 Posted August 21, 2015 (edited) Servo got 7 positions to right/left... it can not stop between... so it can help only partially... Max... Edited August 21, 2015 by MaxSupercars Quote
LegoCube Posted August 21, 2015 Author Posted August 21, 2015 (edited) Yea, i ended with 7 steps right and 5 left... The min/max didn't do anything as far as I could tell... I tried .07 offset and .14 offset at both limits Edited August 21, 2015 by LegoCube Quote
MaxSupercars Posted August 21, 2015 Posted August 21, 2015 I got Idea... put one middle gear between your 2 gears... then will be the teeth on 1st and 3rd gear aligned right... Max... Quote
LegoCube Posted August 21, 2015 Author Posted August 21, 2015 (edited) Max, sounds good. How does one get a 90 angle from the steering axle to the Servo with 2:1 ratio using 3 gears, though? In a compact way... Lots of nice ideas to play with :) Edit: tired typos Edited August 21, 2015 by LegoCube Quote
LegoCube Posted August 21, 2015 Author Posted August 21, 2015 (edited) If anyone finds this useful I managed to find settings for SBrick to achieve what I wanted through loads of trial and error. These settings in SBrick Designer make Servo work as a 13 step motor instead of the default 15. That means there are equal 6 steps to left and right. More importantly it fixes the axle rotation offset I was experiencing. Picture of my steering element for these settings: I would prefer a more clean fix and will rebuild this module after I get my 14 tooth bever gears... Edited August 21, 2015 by LegoCube Quote
MaxSupercars Posted August 21, 2015 Posted August 21, 2015 I made an example for you with 3 gears... Max... Quote
LegoCube Posted August 22, 2015 Author Posted August 22, 2015 (edited) I made an example for you with 3 gears... Cool! Thanks :) Edited August 22, 2015 by LegoCube Quote
LegoCube Posted August 23, 2015 Author Posted August 23, 2015 I thought I'd get a break from the steering element and move on to the paneling. Also I thought to give the LDD another shot. Here are some early shots :) This time there is no actual problem but comments and suggestions for improvements are higly appreciated :) Actually there is one question. Is there a flex cable or any other part to fill that short cap between the 2 topmost panels? If moderators don't mind the title could be renamed to "[WIP] [MOC] True Ackermann RC Concept", Thanks! Quote
Victor Imaginator Posted August 23, 2015 Posted August 23, 2015 Sad, i'm far away from bricks... But at least i have LDD and puzzles to solve) Quote
LegoCube Posted August 23, 2015 Author Posted August 23, 2015 Cool! Thanks Victor :) Second and third look awesome! Quote
LegoCube Posted August 23, 2015 Author Posted August 23, 2015 (edited) I played with the bricks I have and got something like this. It is far from solid and there are still some color errors but it is getting there. I would have been stuck without your help Victor. Thanks for showing the way I found a Hero Factory set with those 'H' bricks. So taking first step from concept testing to my plan to make a Honda Edited August 23, 2015 by LegoCube Quote
LegoCube Posted August 23, 2015 Author Posted August 23, 2015 Progress so far. IN the background an alternative I started :) Seriously enjoying this. Thanks for all the feedback. Laters! Sorry for the bad quality pictures. Quote
MaxSupercars Posted August 23, 2015 Posted August 23, 2015 I like that you got fun... before you go ahead with panelling I advice you to make chassis with suspension and wheels... after that you should continue with panelling because than you realize how much space you got where... :) Max... Quote
LegoCube Posted August 24, 2015 Author Posted August 24, 2015 Thanks Max. Yea I tried to roughly keep the proprtions so that the fron panels would not obstruct the wheels from turning and stuff like that. Last night I built the elements together to see where to focus next. So here are some more bad quality pictures Sorry for mass posting. I think some might find this uninteresting and annoying so slowing down on updates until I have more urgent problems. The community feedback has proved and important tool :) I am fairly happy how the front looks like. I would like to have slightly larger headlights but I am fine with some compromises with my first MOC :) I am pretty happy how that wheel turns inside the frame :) I do not think I will add suspension for this car. I want to keep it simple and lightweight. I only own the heavy suspension from 8070 and 42029. They are so hard they don't actually do much. I only drive the R/C for short tests on livingroom floor :) Quote
Technic Jim Posted August 24, 2015 Posted August 24, 2015 I found a Hero Factory set with those 'H' bricks. So taking first step from concept testing to my plan to make a Honda Lol! Good idea though! Quote
LegoCube Posted August 27, 2015 Author Posted August 27, 2015 This thread started with a steering element from Sariel and it is going to continue with another steering element from Sariel. I was surprised I had all the pieces :) I just hope my F40 arrives in mail tomorrow. I will know what to do this weekend. Nice timing Quote
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