building a robot transport

[bskll]

my team is interested in building a motorized cart that help us transport our heavy robot.

the total amount of weight that the motors has to support is about 130 pounds for the robot and about 20-30 pounds for the cart it self.

we are planning to drive it with a simple drive system of two motors each individually connecting to a chain and then the chain will connect to 1 wheel each.

what gear ratio do you guys suggest? we don't need it to be fast here. we just need to help move along the robot.

thanks for any suggestion.

P.S. this is my first post.

[Waynep]

Roger,
Congrats on getting onto the Forums. I hope you become a frequent poster. To answer your question on gearing, it really depends on the type of motor you intend to use. So if you send us back what motor you want to use I'm sure we'll be able to provide you with gear ratio selections. Good luck with your cart.
-wayne

[Greg Needel]

i agree with wane that we need more information to help you out...please also note that FIRST discourages motorized carts at regionals and nationals. but i would say if you are still going to build one make it as small as possible because that will also have to fit in your pits at regionals.

[[527]phil]

team 1114 had a motorized cart last year, since we're getting different motors this year i suggest using the old drill motors with the helical gearboxes, i don't think anymore gearing is required after that, just attach the wheels directly to the gearbox, it seemed to work for them

[Holtzman]

Originally Posted by [527]phil

team 1114 had a motorized cart last year, since we're getting different motors this year i suggest using the old drill motors with the helical gearboxes, i don't think anymore gearing is required after that, just attach the wheels directly to the gearbox, it seemed to work for them

That cart was my little baby. It was an offseason project to determine weather a CVT was viable. As it turns out it was. It used 1 drill motor with the planetary gearbox, and a set of variable diameter pulleys from www.hi-lo.com
They worked by having 2 pulleys that expand and contract. One is spring loaded, while the other one has a handwheel that turns to vary the pulleys diameter.

It worked out quite well for our application, and achieved a speed of 2tf/s in the low end of the CVT and about 8ft/s at the high end. I also played around with the sprocket ratios on the wheel to make it go faster for racing around the halls at school.

I don't think the variable diameter pully system is the way to go for FIRST robots. the system is
1. bulky
2. heavier than many 2-speed designs
3. harder to control than a 2-speed, since you need to have a motor and a potentiometer to change the gear ratios. For our application, we just turned the knob on the bottom manually.
4. Although we never experienced any slippage in the pulleys, the chance exists under high loads.

All in all, building a cart can be a good offseason project, and can be a good test platform for new designs. Or you can just put a sound system in and make it look cool, either way, carts are cool.

[IndianChieftain]

if the reason anyone is building a motorized cart is so that it stands out, then there are lots more ways to build one. for example you can put a boom box on the cart and power it with a 12 volt battery. or police lights. those will certainly make the robot and the team stand out

[[527]phil]

hmm how bout a disco ball, strobe lights, and a dj, that'll make a cool cart for the pits, lol, i think evryone should keep it simple, the competition is about the robots, not the carts, you can have the greatest looking most complicated cart, but if your bot sucks it really doesn't matter.

[Bcahn836]

Originally Posted by bskll

my team is interested in building a motorized cart that help us transport our heavy robot.

the total amount of weight that the motors has to support is about 130 pounds for the robot and about 20-30 pounds for the cart it self.

we are planning to drive it with a simple drive system of two motors each individually connecting to a chain and then the chain will connect to 1 wheel each.

what gear ratio do you guys suggest? we don't need it to be fast here. we just need to help move along the robot.

thanks for any suggestion.

P.S. this is my first post.

Cool we are doing almost the same thing. For my senior project we too are building a motorized cart to carry the robot. Except we are using two wheel chair motors that were donated, we have the motors in a direct drive straight to the wheel chair wheel. Even might use the controls from the wheel chair too.

I have no idea on the correct gear ratio, we almost used the chain drive using an electric car motor, but my teacher brought out a donated motorized wheel chair and that quickly changed our minds.

GOOD LUCK.

[Koko Ed]

I would recommend making one as light and simple as possible.
While it is really cool to have one with alot of bell and whistles you should remeber that the more stuff you put on it, the more it weighs and the more it costs to transport is (not to mention the amount of space it takes up).
Think of keeping things more functional than fancy. That goes for the robot as it does the cart.

[[527]phil]

and don't forget that if you burn out a motor you'll be carrying the robot, or switching a motor, i think i'll just stick with an old fashioned cart cuz if it aint broke don't fix it, plus we got a load of freshmen to pull it for us , lol

[Ian W.]

Originally Posted by [527]phil

and don't forget that if you burn out a motor you'll be carrying the robot, or switching a motor, i think i'll just stick with an old fashioned cart cuz if it aint broke don't fix it, plus we got a load of freshmen to pull it for us , lol

Nonsense, that's the beauty of doing a chain drive, if a motor dies, take out the master link, put the chain somewhere safe, and now you have a slighty heavier push cart, which you can easily make back into a motorized cart should you find another motor.

That being the case, I suggest trying to use a CIM, or something else that will be in next year's KoP, or similar to something in it, because that way if it dies at a competition, you could possibly get replacements from other teams with a bit of trading. Or just use somethin that won't burn out under normal use (like a wheelchair motor, think of the trouble a company could get into for having their wheelchairs dying).

[sanddrag]

While motorized carts are really cool, I would not recommend one at all. When you're about to miss a match, a freewheeling cart will get your bot to the field much faster. Also, a non-motorized cart is much afer for everyone else in the pits.

[Doug G]

This comes up every year on our team, to build a motorized, super-duper, fancy dancy cart with toolboxes, battery charging stations, etc.. etc... I say keep it simple, light weight, and collapseable if possible. And just how is it getting to the competition - in the same crate as your robot? If the competition is too far to drive it to, are you willing to build a second crate to ship this cart in and pay for the extra drayage and feights charges, hmmm?

[Bcahn836]

we have always used our cart as a shipping crate for tools, and had it non motorized, but if you remember at Atlanta it was a pretty good distance and always up hill and the same 4 people got stuck pushing it from pits to playing Field, after last year i am tired of pushing that cart, so we are building a motorized on that will work like a lawn mower with a power assist. And we will still be able to use the cart as a shipping crate with tools we would just have to un hook the motors and unbolt the casters in front and board up the sides. Oh and it is only 10" bigger than the cart we used last year that fit in the pits just fine.

[Wetzel]

Originally Posted by bskll

the total amount of weight that the motors has to support is about 130 pounds for the robot and about 20-30 pounds for the cart it self.

I think that your weight estimate is low. With space in the pit at a premium, we use our cart as a work table too. That means we hammer and bang on it, as well as moving arms around with puts other pressures on it. Tools also can get carried on it, and are nice to have at the field, or sometimes necessary as the robot is worked on en route to the field, or during the elimination rounds if you are so lucky. Also, it only weighs about 30 lbs and comes apart to fit into the crate for shipping with the robot.

Not to discourage you from building a motorized cart, but I think that you are way low on your load estimate.

Wetzel