Low-Rider Robots

[sanddrag]

I believe our ground clearance is around an inch. We would go either a little lower or a little higher (to drive in goals) but the ground clearance is dictated by our wheel size and frame design which is dictated by our gearbox output speed. We did some real world tests and we feel that on a flat playing field, the CG does not have to be quite as low as we thought to remain stable. So, an inch it is.

[Ianworld]

We have about 1.5" to 2" inches of ground clearance. Just enough to get over the goal bases. We're not sure if we'll need that clearence but i think its better safe than sorry. Of course for pushing you'll be pushing against something with a ground clearence of .25 or higher depending on how hard you push.

[SteveO]

Originally Posted by D.J. Fluck

I'd think you'd almost have to be a low rider for this game if you plan on stacking more then one tetra at a time or plan on stacking pretty high....unless you like getting tipped or can prove otherwise. I think we're planning on having less then 3" of clearance, but i am not 100% for sure.

Then again, I have no mechanical design ability....im sure someone will prove my statement wrong

Anybody have an anti-tip mechanism We are going to try and use the accelerometer to automatically deploy "wheelie bars" if we are tipping a certain angle. We want to use probably pretty big pistons for this though and were heavy as it is

[HPA_Robotics_13]

Our robot's drivetrain and wheels were inspired by team 121's low-riding colson wheels. We also have 4" wheels, which puts our chassis at about .25 inches of clearance. The problem is that the chassis bolt heads stick down about another .125 inches, this means that we cannot clear the HDPE loading zones.

Team 121: do you guys have .25 counting those bolt heads?

currently we are running a two wheel drive. On the front we have 4" omniwheels and on the back we have the 8" skyway wheels that we lifted up to match the clearance of the omnis.

Does anyone have any thoughts on how this will perform? We're going to do our first carpet test of this drivetrain tomorrow. I'm planning on putting some pictures up soon.

[NoodleKnight]

Originally Posted by SteveO

Anybody have an anti-tip mechanism We are going to try and use the accelerometer to automatically deploy "wheelie bars" if we are tipping a certain angle. We want to use probably pretty big pistons for this though and were heavy as it is

Yeah, our arm. Actually, it really depends on what drivetrain we want to pick (yes, I know its week 4, apparently we're building 3 different drives...). But if it's the kit bot, we have an anti tip mechanism which is essentially a set of outriggers powered by the window and van door motors.

And, about 2" of clearance -- it can be reduced though.

[Rob]

Originally Posted by HPA_Robotics_13

Team 121: do you guys have .25 counting those bolt heads?

We bought flathead bolts and countersunk all of the heads that were on the bottom of the chassis so they are flush with the bottom. This is pretty easy to do and will solve your problem.

Hope this helps!

Rob

P.S. your setup should work great if you are powering all four wheels, you will have to do testing to determine if there is enough traction to manuver with only 2 powered wheels (its probably fine though)

[Kyle]

Originally Posted by SteveO

Anybody have an anti-tip mechanism We are going to try and use the accelerometer to automatically deploy "wheelie bars" if we are tipping a certain angle. We want to use probably pretty big pistons for this though and were heavy as it is

in 2003 our robot had wheelie bars that were spring loaded so when the bot started to move the wheels pulled a string that pulled a pin to release the bars, it was light weight easy to make and replace. And it saved our bot from tipping more times then i can count.

[HPA_Robotics_13]

Originally Posted by Rob

We bought flathead bolts and countersunk all of the heads that were on the bottom of the chassis so they are flush with the bottom. This is pretty easy to do and will solve your problem.

Hope this helps!

Rob

P.S. your setup should work great if you are powering all four wheels, you will have to do testing to determine if there is enough traction to manuver with only 2 powered wheels (its probably fine though)

Rob, you think it would be a good idea to power the omnis on the front? With so little traction, would it matter? I suppose they have high forward and backward traction, so it would be good to drive them for that reason. But it wouldn't help for turning.

I was watching your third episode of American Robot and saw that you guys have a whole lot of control even with high traction wheels on the front and back (and middle!). Maybe it would be better to just put non-omnis on the front and drive them?

I already made an Ace Hardware run and bought all the bolts I need, and a new countersyncing bit, for mounting our electronics. I didn't even consider that we could countersync those chassis bolts. Duh! Thanks for the wake up call.

[Brandon Holley]

Team 11 is gonna be cruisin .25" off the ground this year. Our frame is also gonna be very effective in the anti-tipping ability. Our arm also has the ability to right the robot up, and we will most likely have a set of outriggers (wheelie bars)

[Rob]

Originally Posted by HPA_Robotics_13

Rob, you think it would be a good idea to power the omnis on the front? With so little traction, would it matter? I suppose they have high forward and backward traction, so it would be good to drive them for that reason. But it wouldn't help for turning.

I was watching your third episode of American Robot and saw that you guys have a whole lot of control even with high traction wheels on the front and back (and middle!). Maybe it would be better to just put non-omnis on the front and drive them?

I already made an Ace Hardware run and bought all the bolts I need, and a new countersyncing bit, for mounting our electronics. I didn't even consider that we could countersync those chassis bolts. Duh! Thanks for the wake up call.

Well, here are my thoughts. Remember that these are just opinions based on how I like the robot to manuver. You have to decide if you want to be able to be a pusher or have high manuverability. It sounds like you are going for manuverability. I prefer to have a robot turn around its own center, and if you have 2 powered wheels at the back it will turn around the back end. I just think this makes it easier for the driver to control.

Now, if you add powered non-omni wheels on the front, you have to recall that the wheels will be sliding sideways when you turn, causing friction. This can be both good and bad. A good amount of friction will make the turns very controllable as the robot will fishtail less. Too much friction will make you turn slow and draw lots of current while doing so. You really want a trade off of thiese elements. There are many threads on these boards about drivetrain ideas, and 2 vs. 4 vs. 6 wheel drive. Many people have offered their experience and knowlege to those debates. I suggest searching for them and reading up on them. Rember that your drivetrain should be a function of what you want to do, so set some performance goals and then give it some thought.

Also remember to test out your machine at the full competition weight! Try it with your current configuration, you might find that you like it alot and want to keep it.

Im glad the countersinking helped...

Best of luck, and feel free to PM me or some of the "much more knowlegable than me" people on the boards if you have any further questions!

Rob

[RogerR]

Originally Posted by MORT~11

Just a quick tip on the .25 " ground clearance....the loading zones are .25" HDPE

does anyone know how the HDPE is attached to the field? is it velcroed to the carpet, and if so, how does this affect the height of the HDPE? (i.e. will the velcro add 1/8" to the height, making the loding zone .375")

[cadman2k5]

yea Team 637 knows what it feels like to flip... NOT FUN. were goin low too.. not a quarter inch... but low.

http://www.njfirst.org/galleries.htm

check out the upside down Marotta logo pic

[Iain McLeod]

358 used to be .25'' but now we're about an inch.

I was really worried about flipping and crushing tetras this year too... everyone tells me that i'm exaggerating the danger, but i still vividly remember riding up onto balls many many times both last year and three years ago.