![]() |
Re: 6WD vs 8WD
Quote:
As you raise the wheel (or increase the center wheel drop) you decrease the load on those wheels. Yes, it decreases the sideways slipping force on the wheel, but it also decreases the tractive force in the same proportion. The first point is that it never really behaves like a omni wheel, just as a wheel with less traction. The second point is that the load drops off across the distance of your wheel dropped (teams range from 1/16-1/4") which makes it hard to tune. I worked with an adjustable drop 6WD for a few years and we discovered that 2-3mm drop was what worked for us as optimum. Outside that sweet spot we began to get significantly different driving performance. We also discovered that a 1/2 day of matches was enough wear on gum rubber treads to get us outside this range. We eventually decided that it was not worth the effort and decided to let the wheel off the ground and allow the robot to rock between the two 4 wheel systems. It was much simpler in the long run and allowed us to apply our resources elsewhere. I know the 2011 kitbot configuration has enough lift to accomplish this. You may want to spot check with teams to see if all of their wheels are actually on the ground or just really close. How might having one set of corners off the ground affect the logic you used above? |
Re: 6WD vs 8WD
For Logomotion, we had an 8WD chassis with 6" wheels. The four at the corners were "kit" wheels. The four in the center were closely spaced pneumatics with adjustable drop. (I noticed in St. Louis that 330 used the same arrangement). We adjusted the tire pressure and center wheel drop so that the corners were about 1/16" off the floor on a hard surface, and had light contact on the carpet.
We were quite happy with the arrangement. It turned very well, since the pneumatic tires had better traction and higher loading than the corner wheels. It didn't rock or bounce during accelearation or turning since the corner tires were hard. During acceleration or in a pushing situation, all four pneumatics and one set of corner tires were in contact with the carpet. It was very difficult for others to push or turn us. It was a good balance between the agility of a 6WD with center drop or omnis, and the pushing power of an 8WD with pneumatic tires. |
Re: 6WD vs 8WD
eight
|
Re: 6WD vs 8WD
Quote:
|
Re: 6WD vs 8WD
From my experience, the 8 gives you more stability at higher speeds and better predictability of how the robot will handle. We also decreased the diameter of the outside wheels instead of offseting the axle height.
mike d |
Re: 6WD vs 8WD
Quote:
|
Re: 6WD vs 8WD
no change of ratio, just let it ride.
|
Re: 6WD vs 8WD
Quote:
|
Re: 6WD vs 8WD
Personally, I like 8WD, although my opinion might be a bit biased because I haven't driven a 6WD robot anywhere near as much as I've driven an 8 wheeled one.
This year my team used eight 4" diameter wheels geared 7:1 and I loved it. Here is a video of us playing with the chassis a week into build season: http://www.youtube.com/watch?v=inI40uMKuEE If I remember correctly, the center two wheels are dropped 1/16". We later added another two motors to the drive train which gave us a nice balance of speed and power. |
Re: 6WD vs 8WD
Quote:
|
Re: 6WD vs 8WD
Quote:
Key Features are: -Cantilever Wheels -Direct Drive -Inline system -CAMS -Sliding Bearing Blocks -Small Wheels (We goofed, big wheels are ugly :P) There are a few other tidbits, but that should sum it up. -RC |
Re: 6WD vs 8WD
Quote:
-2 speed -Custom gearboxes -Custom wheels |
| All times are GMT -5. The time now is 16:54. |
Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi