I’m attempting a drop center hybrid base. It should be sub 10 lbs with batteries.
Not really rebuilding persay but we are building a second robot. A light weight front dumper, we will decide which to take to nationals and worlds in a week or two.
We are to cut weight and to paint. Also to adjust motors a tad. Im not quite sure what is up with all the drop center hype though. 62 did it and now everyone is trying it, but thats not going to turn everyone into 62. 6834 surely will be amazing either way, I just dont quite understand, am i missing something?
I was skeptical at first. I don’t use it just because 62 did. Once upon a time we had a high speed 4-inch tank drive. It burnt out when turning with objects. We switched to drop center and it didn’t anymore. Magical.
We are totally rebuilding right @Carl ? We’re going to have 2 bases have 3 motors each (left wheel, right wheel, and a mechanism to keep us from getting pushed) and drive to each side of the field in autonomous with friction mat in the middle that is rubber banded to go up without motors. Then we’re going to have a catapult with a 2 motor base and a 4 motor forklift/catapult scoring over the wall.
We moved to a drop center to try to improve traction with loads. We found that it’s worse than a standard tank drive and we’re moving away from it.
Rebuild for the win! Never made a drop center hybrid base, nor do I plan to. Don’t think attempting a new design I have not done before is a good idea with state being next week and worlds a little over a month away.
I tried a drop center but didn’t see a huge benefit… our b team uses one though. We didn’t do a full rebuild but definitely changed our bot up some. Excited to see u all in April!
What is a “drop center”? @Scarr
A drop center is where you have a 6 wheel tank drive but the middle wheel is lowered and the only one that’s powered
We are keeping are current robot and building another one as well. If the drop center isn’t any good, I’ll probably convert it into a baby base and try that out. This is the first chance I’ve had to try all the different designs and put my own spin on them. I would really like to build a front dumper as well, but I don’t think that I’ll have the time to reprogram my muscle memory for driving. I do however believe that it will be a front dumper and back dumper that will win worlds together.
We talked about building a base that was powered from the center back in October, when the first problem that we noticed from our robot was that it was prone to forward tipping when we lifted and floored it in reverse because we powered the front wheels as well as the rear. We overcame this through weight distribution but as the robot became heavier we had to use the smaller wheels to avoid stalling, and this made our base slower when we had to cross the entire field. This is fine as long as we only have to cover our side of the field because there is almost no difference between the baby omnis and the 3-1/4" over a three foot span; but as you know sometimes your alliance falls over or stalls out. So as the season progressed our drive got slower but our lift kept getting faster. Since regionals we have figured out how to make our lift about 20% faster, so all we’re trying to do is match our drive to our lift.
We don’t use it because 62 did it. The capabilities of a drop center are amazing. Speed and almost impossible to burn out
Did you use 4" or 3-1/4" wheels for the center? Also how wide were the center wheels or what was the distance between them? We are starting out at 10" and experimenting from there. We also plan on using 3-1/4" omnis with 6 motors, at least that’s how it’s built so far.
We used 4" wheels in the center. We played around a lot with the spacing between the wheels and the wheel sizes. We also iterated between motor distribution, starting with 6 motors and moving to 4. The distance between center wheels was always maxed out (about 17" apart) for maximum stability.
We started out with 3.25" omni wheels and 4" wheels. This worked great while we had pneumatics – the extra weight at the bottom distributed the weight perfectly. We never tipped and got pretty nice traction. From here though we moved away from pneumatics due to an issue, and we started tipping. Finished 2nd to last in qualifications because we were on our backs for all but 1 match. We moved the lift towers forwards 0.5" and moved the wheels about 3 inches forwards and added standoffs at the very back that served as anti-tips. This worked great – until we went to hang, where the standoffs would catch and prevent us from hanging. Eventually we’ve moved to pulley wheels on a c-channel at the very back. This served us well in competition, but turning was pretty sketchy since pulley wheels don’t have omni-rollers. After states we’ve been playing around with wheel sizes and found that 2.75" wheels on the front/back work reasonably well. However we’re tired of dealing with these crazy traction issues – the 4" wheels skip a lot, and although it has improved quite a bit since we started, we’ve seen many examples of regular tank drives performing much better in terms of traction and we have decided to move in that direction. Good luck!
The problem with drop center two-wheel drive (or any 2wd) if you have a fast ratio is that although your motors wont burn out, the wheels will slip a lot during acceleration and deceleration making the robot much more difficult to control.
Basically will be doing this with our robot and adding a couple of gizmos to stand out lol. On a side note, agree 100% with the drop center hype. Just because another team did it, doesn’t mean you’ll be able to replicate and perfect it. The lost of traction is simply not worth it in our experience and it made it very difficult to collect stars.When you try to drive around with the arm raised and have heavy loads, navigating is especially hard because the robot tips forward. In many videos you’ll see robots carry and throw decent loads but their dump cycles are a lot slower because they are so slow at backing into the fence. We’ve gone through many drive setups this year and are finally happy with what we have now. Consistency is going to be important this year.
The bot we used all season has a 6 motor drive on the baby omnis. All of our motors are towards the front, so we have a long chain connecting the back wheels. There has been more than one occasion where the chain was disconnected and only the front wheels were powered. The only difference that I noticed was that it seemed to want to tip forward a little easier than normal, but it was very minimal after it was weighted properly, the turning was also little faster and the bot didn’t want to tip backwards as easy; as far as traction, there was no difference. The only reason I didn’t switch to a front wheel drive was the programming. We scored 50 points in autonomous with timed functions, without a lift.
Thanks for all the information. I’m almost done with this iteration and I should be able to post a video of it driving around on the field either tomorrow or the next day.
No problem, glad to help. We found that the traction issues came from the entire robot leaning forwards when picking up a large load, thus bringing the CG so far forwards that the middle powered wheels were only barely touching the ground. Powered front wheels would avoid this issue completely, which is probably why your traction saw minimal changes when the chain was disconnected.