I’m having issues with steering on my 6 wheel rover, as in it’s almost locking up when its turning (the tyres aren’t touching the frame) which makes the turns very slow. Video of it running here (apologies for the quality): https://youtu.be/LkIZuSkB47U
Motor direction is fine. It runs forwards and backwards no problems. When off the ground, the steering seems to work fine too: https://youtu.be/Ms0mNt6d2VY
I’ve studied the wiki and tried different PID settings, turn rate, etc. but i’m not quite sure what i’m doing to be honest.
I am starting to wonder 3 things:
Can it better tuned to achieve the turn rate
Are the wheels/tyres to narrow
Are the motors not powerful enough (I’m running on 7.4v and have tried with 12v with small improvement, but not much)
I never build a rover with a rocker bogie suspension, but all I have seen do not use skid steering, but steering wheels at the front and back. Skid steering puts great forces on the chassis, because the wheels are dragged sideways. You can observe the rocker bogie arms bend sideways in your video. Most skidsteering vehicles use a short as possible wheelbase or try to put more load on the middle wheels for 6x6 vehicles. You could try to put wheels with less grip on front and back. To test if that would change anything, you could wrap the wheels running surface with tape. But even with less grip, I fear the stresses will wear down the rocker bogie links quickly.
I agree with @count74 - your setup does not lend itself to skid steer. I created a rocker-bogie rover too but had the four front/rear wheels as castors and only drove the centre wheels. If your motors are under powered and your traction is good (as it looks to be with rubber tires on tile floor) then you would expect your vehicle to struggle in turns. Perhaps try wetting the floor to reduce friction to see if this may be the case?
It is not clear in your video if wheels on opposite sides actually go in opposite directions when turning? For a diff drive vehicle with no throttle input, you should get the wheels either side going full speed in opposite directions with full steering input.
Thanks for the replies. Thats really interesting and useful. The design of the frame is taken from this 3d printed version: https://www.thingiverse.com/thing:1318414
Never considered that it would be difficult to steer but I guess the traction of the tyres in this case make it too grippy to slide. I will try with slicker tyres (maybe plastic printed on front and rear to see if this makes a difference, but I am interested in installing servos for steering on the front and rear. I might look at 3D printing a replacement holder for the motors.
@jimovonz: the wheels do spin in opposite directions when turning but I guess the 7.4volts make it less powerful to do so efficiently. Could you share a picture of the castors on your model? So I can get an idea of a design for printing
@joes2021 I made this rover a few years back and I can’t seem to find any pics. Here is a video of my daughter having a go on the remote. This was in the very early stages and it ended up with larger wheels in the front to allow it to get over bigger obstacles. Unfortunately this vehicle (and others!) were lost i when my shed burnt down. Hopefully it gives you some inspiration
Thats great! Much appreciated. Very sorry to hear about your shed though that’s my worst nightmare. Hope you managed to replace the contents.
Definitely had some inspiration from your video. Been having a look at some modifications I can make and either a castor or servo design looks best. Going to make a few prototypes up and will share on here when complete. Thanks again for your help
that’s my worst nightmare. Hope you managed to replace the contents.