Pro's and Con's of Motorized Robot Carts

[fox46]

I believe what it comes down to is quite simply: Haters gonna hate

A motorized cart is only as dangerous as its operators and design. I think the FIRST community contains some extremely hipocritical ideas when it comes to *safety*. For the most part, the ones complaining that these things are unsafe are really just sore because they didn't have the resources, foresight or skill to build one themselves. This is apparent from the overwhelming praise we have recieved for our efforts and the handful of critisisms.

CONS:
-potential for breakdown
-diversion of team resources
-difficult to transport
-another item requiring maintenance

PROS:
-Increased safety (brakes, controllability, reduction of strain injuries)
-An excellent team building and learning exercise
-Convenience at competitions/mobile pit
-Marketing tool (helps improve team image)

The first motorized cart I helped build was with team 854. It was a ride-on unit built by frankensteining the hardware from an old wheelchair to a custom chassis with automotive steering which also allowed for a 0 turing radius. It was maneuverable, had a lighting system on it to make it conspicuous and a motorcycle horn which had been wrapped in tape to make it quieter yet effective at notifying people you were behind them. It was a great project for the younger members to learn skills which later helped us build some great robots. It was also designed to be an integral part of the pit setup providing a work surface and a place to keep things like spare parts, tools and batteries.

The second motorized car I was involved with was for 2013. It was also made by frankensteining motorized wheelchair components to a custom frame. It had three onboad marine batteries (two for 24V propulsion, one for on-board power). It had 1500W of 120VAC power and 12VDC outputs as well. It too was equipped with lighting and a sound-deadened horn. This version was much more functional than the 854 model using only wheelchair steering but included much more storage space as well as a telescoping floodlight for field-side robot repairs during eliminations. It too was an integral part of the pit and served as both a tool cabinet and primary work surface.

The third motorized cart I helped out with was also for 2013 and was more of just a fun toy for around the shop than to be used actively at competitions. This unit was built from a small 2ft cube steel cabinet with a door. It had a tricycle setup where the operator would sit on the top of the cabinet with their feet over the front. There were two wheels under the "cube" and a fork/handlebar assembly at the front. It was powered by a single CIM motor and planetary gearbox powering the front wheel. The battery was a tired old MK robot battery also mounted to the front fork. Control was provided by a variable speed ESC from an old cordless drill which was mounted to one of the handlebars like a throttle lever. The ESC had a forward and reverse function like the drill as well as a brake function when released. This cart was fitted with a sound-deadened horn and lights. It had team sponsors and name displayed like the others before it as well as a few "WARNING BATTERIES ON BOARD" graphics because inside was a 5 bay TecMate Accumate 5 charger, stock of battery acid neutralizer and ventilation fan. This cart would sit in the corner of the pit area and took care of all battery charging duties. It would charge 5 batteries at once and would hold up to ten. During eliminations it could be driven out to the field and plugged in to the aforementioned robot cart to provide field-side charging.

I am a huge proponent for motorized carts because of the additional safety they afford. I can't tell you how many times I have seen teams pushing their robots at a running pace. A motorized cart is speed limited. I also remember at the houston championship, teams struggling to push their robots up steep concourses and frantically trying to slow them as they barreled their way down. As long as these things are built and operated with respect like you use any other cart they are just as safe if not far safer.

The only reason team 3756 didn't have a motorized cart this year was because the wheelchair chassis they purchased did not come with the control interface (joystick) and we were unable to find one in time to build their cart.

Issues: Now here is where I get frustrated. In boston, 2013 was told that they had to push their cart rather than drive it with no reason or explanation given. They put the motors in freewheel mode and there was no problem. However, every time, like any other cart, when they came to a cable protector, they had to gather speed to get their robot over it. Motorized, it would simply crawl right over. It was far more difficult to control manually than while powered. This decision by staff to make them push it created several hazards which they continually refused to acknowledge as they were brought to their attention.

At the GTR regional however, the safety inspectors praised the team for their hard work and attention to detail in building it and they were encouraged to use it as intended the entire competition. I myself remember seeing about 7 different occasions where they recieved safety credits from other teams specifically for their cart. By the end of the competition I believe they had 38 safety tokens.

I like the wording in the administrative manual stating that carts must be safe but I challenge those who march about declaring anything that is different, unique or imaginative to be *unsafe*. Those people are indeed limiting the creativity of our teams and "squashing the dreams of young engineers".

If FIRST bans the use of electric carts then I will insist that they also ban the use of segways, golf carts, police patrol scooters and yes, electric wheelchairs at their events as well.