I’ve seen a quite a few robots with short wheelbases and tank bogeys for support. How does this compare with a traditional robot with all 4 wheels in the corners?
Kind of https://vexforum.com/t/forward-versus-reverse/16912/1
A smaller base equals quicker turning. Turning is pretty important this year. That’s why we’re seeing drop center a lot.
Turbo Drop Center Drive Turning - YouTube
Also, having a smaller base means you can have anti-tips already in position without the need to flip out.
But isn’t turn turn torque lower?
Actually, when you have a wider wheel base you don’t need you have more stabilization/ anti-tip. So you don’t need to have anti-tip on the sides. Also, our teams wider base allows our driver to swing turn to add momentum to claw while turning to throw faster and farther.
From a mathematical standpoint, there is no difference in torque if your drive train is smaller. The only ways to change torque are by using a smaller wheel diameter or higher torque motors
I think they mean in turning. If you have a wider base, you have more torque/less speed in turning. If you have a narrower base, you have less torque/more speed.
this season a smaller wheel base gives the advantage of faster turns. However iv’e seen many bot with 6 bar lift or manipulators that reach big heights. As these turn with the manipulators up high i notice that the wheels come of the ground which means the bots have no traction in other more rare cases the bots even tip. My team chose to use a short wheel base and a 6 bar lift so from experience the base loses traction on turns when the lift is up high.
Theoretically, would a well optimized X/holonomic drive be better due to its faster turning? Or is the complexity/friction not worth it?
45 degree offsets on the wheels actually make an x drive go forwards faster than a normal drive. When turning, the wheels are approxiamately in line with the trajectory, so the speed would be the same as if driving forwards with no 45 degree wheel offset. Basically, X drives go forwards faster, turn slower.
Advantages of a shorter wheelbase:
- They are MUCH faster
- They take less outside space
- They help getting objects in the near zone (You’d have to turn to intake if you have a two-bar lift)
Disadvantages of a shorter wheelbase:
- They lack torque
- They burn out extremely fast
- Your robot may only handle so much momentum held before it falls over
Hopefully this helps
This confuses me. What does the size of a drivetrain have to do with the speed? So long as the gear ratio , weight, and wheel size is the same the speed is the same. How does a shorter wheel base make getting objects in the near zone easier? You have to turn no matter what.
As for torque, again the size has no affect on torque (unless you’re talking about turning, which it doesn’t seem like it because this is wrong for turning) or burning out. Care to explain how the size of a drivetrain gives it more speed, torque, or burn out faster?
Because it is closer to the center of rotation, so has to go less of a distance to turn the same amount, like a lever
What does this have to do with the speed/torque of the drive in general? For turning a wider/shorter drive will allow for faster turning. That’s why a drop center turns so much faster. This comment answers none of the questions I posed earlier. The size of your drive does not affect your speed or torque.
wait, r u asking about size as in area, cuz only thing that matters for hwat Im talking about it the distance between your two wheels in terms of width…
I am talking about the distance. That makes no difference in the drive speed or torque.
oh, in that case, I agree, but in my opinion, using pneumatic for base is the fastest…
That, I agree with. What I was talking about was turning. If you were to have a base with 3.75 wheels that are 16 inches apart, by dividing the circumference of the distance between them to find the distance of the course, and the circumference of the wheel, you’ll find out how many rotations to make a full 360 degrees.
Circumference of the course:
Test 1 (Wide wheelbase)
16"(Diameter between the wheels)*pi(Translate to circumference)=60.3"(Distance in inches for a full 360)
Test 2 (Short Wheelbase)
10"(Diameter between the wheels)*pi(Translate to circumference)=31.4"(Distance in inches for a full 360)
Circumference of wheels:
3.75"(Diameter of wheel)*pi=11.8"(Circumference of wheel)
Finding out how many rotations for a full 360:
Test 1 (Wide wheelbase)
60.3(Distance in inches for a full 360)/11.8(Circumference of wheel)= apprx. 5.1 rotations for a full 360
Test 2 (Short wheelbase)
31.4(Distance in inches for a full 360)/11.8(Circumference of wheel)= apprx. 2.7 rotations for a full 360
By decreasing the distance between the two wheels, the diameter of turning is much slimmer, which means less rotations for a full 360. Test 1 with a wide wheelbase takes 5.1 rotations for a full 360 degree turn, as test 2 with a short wheelbase takes 2.7 rotations for a full 360 degree turn.
Here’s a very detailed whitepaper with complete mathematical calculations on the relationship between drivebase dimensions and turning.