Powering a Larger Motor?

[Andy A.]

Lots of good posts.

First off, I'm glad that your planning on using the Innovation First controller. In terms of simplicity, it is ideal. However, there are some limitations.

Check the quality of the 12v coming out of the car. I'm not terribly sure, but I recall that auto electrical power is usally not very 'clean'. I don't know what the RC can handle in terms of voltage variation or current. Just hook a multimeter up to what ever you plan on drawing 12v from, and see if it spikes or is high or low or what not. It probably won't be a problem, but...

This was mentioned before, but I think it deserves some further mention. Radio contact is always something of an issue. The range on the link is like that of a older portable phone (the 900mhz variety). For the purposes of FIRST, its more then enough, since the bot is never more then 50 feet away and in direct line of sight. Your project may not be in such ideal conditions. I've noticed that on older radios, random packet loss and interference can be a problem.

When the RC loses radio contact, all it's outputs will go to null. That means no motors will get power and relays will open. That's great for FIRST, since the 'bot for all intents and purposes can't hurt anyone in this state. This car however, will probably stay in drive, and will probably keep rolling along.

I would strongly suggest a deadman switch, that will turn the car off (or stop it) should you lose contact. I can think of a few ways to do this with the RC, but I'm sure you can come up with something.

Perhaps some sort of speed limiter to? Say something breaks, and the car flys off with the pedal floored. Maybe a little limit switch on the throttle cable or a optical sensor on the speedometer that would see the needle pass 15mph and activate that kill switch. Heck, why not just hook the speedo cable up to some sort of tach and report back the speed to the operator interface? Innovation First has a wonderful dashbored program that lets you view feedback from the RC. Some serious brownie points there, if your up to it.

Yesh... I should unplug my keybored now to shut my self up. Have fun, this sounds like a cool project. Just make sure the parking lot is empty when you go test this thing .

-Andy A.

[Al Skierkiewicz]

Arpus,
You have a lot of good info here already. If the high school team lent you the robot controller then maybe they can lend you some speed controllers (what has been referred to as "victors") These controllers will interface directly to 12 volt motors and give proportional control through Pbasic and the controller. Your project sounds pretty cool right up to the part about controlling a Chevy Nova. Having a 120 lb robot go out of control in a room with a finite amount of energy stored in a battery is a lot different than a 3000 lb car with lot of horsepower going out of control even out in the open. I hope you have some plans in this area and as mentioned before, safety cutouts for the gas and other devices should control be interupted. As for recommendations, the globe motor is likely too slow for any application you have. In most cases, you want to be able to rapidly release whatever you have engaged, i.e. gas flow or steering. Programming plays a huge part in reaction time for motors coupled to other devices. You might not have enough time to test, but I would recommend testing systems on smaller devices first, like a remote control gas powered model. Please get some help from your high school team, they have experience in dealing with the software and reactions times and how to best interface the controller. Do a lot of testing before you put wheels on the ground.

[Greg McCoy]

Just another heads up...

http://www.access.gpo.gov/nara/cfr/w...cfr571_03.html

If you modify this vehicle, you may be breaking the law if you don't adhere to the government's safety standards. I'm guessing at some point you are going to have to drive the thing on the street. These laws are here for a reason, stay safe!

Also, there are laws governing radio control. You may want to check with the FCC.

Not that I'm a lawyer or anything

Good luck...

[ChrisH]

Originally Posted by arpus maximus

For the brakes, we will use a larger, 12V motor (probably a globe motor) hooked up to either a worm gear or, more likely, a sort of rack with teeth... I don't know what it's called or how else to describe it. This will push the brakes. Preferably this motor can spin in both directions, but we COULD automatically return it to the initial off position via a spring.

I assume the vehicle has power brakes. These are usually boosted by using engine vacuum. In older models (circa 1970) it was possible to control the brakes by adjusting the vacuum in the booster. (Not recommended for normal driving, but possible). I haven't played with anything more recent that that so I'm not sure about more modern systems. This might be simpler than trying to rig a motor to run the brake pedal.

As other people have mentioned, this is an awful lot of energy for you to be playing with. It would be very easy for you or somebody else to get badly hurt if you are not very careful and systematic in your testing. The key question to keep asking yourself is "How do I stop this thing if ...?" Then demonstrate the stopping features with the car immobilized BEFORE your take it out and try it in a parking lot.

ChrisH

[arpus maximus]

For all who say this is a dangerous project: I agree! In fact, my two friends and I had to sign a waiver before the school would even consider it! Obviously, safety is paramount.

To put all minds at ease, we WILL be using a killswitch in the case of signal loss (I am assuming the RC can recognize when it has lost the signal, in which case we will have the RC slam the brakes and release the gas line).

The FIRST team at my school has donated 2 victors, which was quite generous!

Regarding moving the car on the road and the legality of the project: we will never be driving the car anywhere but in open, grassy fields. The main site actually has about 10 acres of field with no obstructions. We will be transporting the car to school, but we will clearly not drive it there. We will be renting a trailer to put it on (luckily, my friend drives a beastly SUV).

Thanks for the suggestions about the brakes! That could come in useful! Hopefully it's not too complicated, because we only have about 14 days to complete this project!

Also, thanks to Andy A. for the point about the car battery, we will look into the issue of voltage continuity.

Construction begins this Sunday and ends on the 28th of May. I will keep the board updated on our progress and results, as there seems to be some genuine interest in the project. Part of our presentation is a video documentary about what we did, so hopefully I will be able to upload that on the internet for all to see. If not, I will certainly post pictures! Thanks, everyone!

ARP

ps. - To any programmers: how would one read a value from a joystick input? Right now, writing the code to manipulate the motors with the joystick is one of my chief concerns. Perhaps someone could simply point me in the direction of some sample code? Thanks!

[Andy A.]

Arpus-

A point about the RC and signal loss.

I can't speak with complete certanity, but I belive that the older RC's (perhaps the newer models to) are pretty useless with out a radio link. All thier outputs will turn off, and the RC won't let anything happen till it hears from the radio again. The logic is that should something happen to the robot and the link is lost, it is difficult for the robot to go on a rampage, or hurt any of the refs. The RC can recognize it doesn't have a radio link, but it can't do a whole lot about it.

It is possible to get the RC to preform some simple actions after it loses a link, or is disabled. I'm not sure that this would really be feaseble though, since it requires some fancy programming and electronics or the use of pneumatics.

My first idea was to have a solenoid (perhaps a Spike?) controlled by the RC close the positive lead between the battery and the rest of the car. This way, if the RC loses the radio link, the solenoid will open, and the car will lose electrical power. This should kill the engine, and with the transmission in drive it outa stop quickly enough. The same result would happen if you had a disable switch hooked up to the compition port of the UI. It would be simple enough to use a Spike to controll a 12v solenoid. Bit of a multistep process, but I think it could work out well enough.

I would be very intersted in hearing how you plan on disabling this sucker if the RC loses it's link.