Powering a Larger Motor?

Technical Electrical
1

All right, before I write my question, let me just get one thing out of the way: I have absolutely no experience with robots, but decided to undertake building a (somewhat simple) robot for my senior project this year. I am not affiliated with the FIRST team at my school, but I am gradually learning a few things from them. One thing they could not answer, however, was a question about powering a motor, and they told me to post the question here.

Okay, so, anyways… The robot controller that I am in possession of only outputs 5V to work motors, LEDs, etc. However, I need to use a larger motor that requires about 12V. What is the best/easiest/most efficient way to make this motor work? I will be using a joystick to control the motor.

This may be a really vague, difficult question (or conversely, hopefully a really EASY question), but any help is greatly appreciated. Feel free to email me ([email protected]) or just post here.

Thanks in advance,
ARP

2

You’ll obviously have to be using a different power source for the motor in order to provide the currrent needed. I only really know how to do this with parts from FIRST kit…so you may want to still talk to some of the robotics team members to decipher what I mean. If your wanting to controlthe motor with a joystics, you’ll have to use either a spike or victor, depending if you want variable speed control (victor), or simply relay (on/off) control (Spike). The spikes and victor obviously have power imputs and outputs, where you will have to attach them to the power source, and then outputs to the leads on the motor. I’m assuming that controller will be simular to the FIRST ones here, so you’ll have to attach the Spike or Victor by a pwm cable to the appropriate port on the controller. The Victor would go to a pwm port, while the Spike would go to a relay. As for the programming…I’m not the person to ask.

Good Luck…and if this made no sense to you…just leave me a message, and I’ll try to explain it better. If you bring this to someone on your robotics team, they should be able to show you what I am talking about.

3

well my question is how do the outputs on the robot controler interface with the motors. it is normal that you use the robot controler to power a speed controler (kind of a scaled relay) while the power for the motor come from another source. any information about the controler would help us give you a solution

4

1.) the lego RCX trick wayish thing… get a 5v motor. connect the motor to a switch. have that switch connected to another power source(12V) & the 12Vmotor. so basically your 5v motor will mechanically operate the mechanical switch to operate the 12v circuit(motor).

2.) must you use full 12V? a 12V motor will run with only 5V. not as powerful, not as efficient, and i think not really good for the motor? maybe not… i dont know about that part.

3.)stepup transformers may work… but id worry about the amps involved. never really tried using one of these before…
E=RI so if you double E, Iwould become double… i think… ive never learned anything about electronics… all my knowledge comes from trial and error… someone clear up what im trying to say, thanks.
http://www.williamson-labs.com/basic-ele-pt-2.htm
near the middle of in the posted url above, there is a simple diagram of a step up
howstuff works explains too


but they explain stepdowns. think opposite of that. less windings on power source side, more windings on output.
sorry if im orribly wrong. yeah, someone needs to help me explain and correct me if im wrong.

5

you can do this by just using a 5v relay and letting the relay act as the switch that turns power on to the 12v motor

6

sorry… may i ask what a relay is?? :confused:

7

A few questions:

1.) Do you need full speed control over this motor? Would a simple on/off function work? Do you need it to run in both directions?

2.) What controller are you using? Do you have any documentation on what it’s outputs are?

3.) What kind of budget are you opperating with? If money wasn’t an issue, I don’t suppose this would have even been a problem.

I can imagine a few ways to do this. With out knowing a little bit more about your situation, none of them would likely do you much good.

-Andy A.

8

a relay is a switch powered by an electomagnet. by putting power the the relay the magnet closes a mechanical switch. if you put a relay inbetween the 12v power and the motor then apply the 5v power to the relay you will then have a control of power to your motor

in FIRST terms a relay is called a spike

9

ahh. i see. thanks. but then you dont have proportional control over the 12V motor right?? with a motor instead of a relay, you CAN get proportional control over forwards and backwards. a little complicated but yes, possible
maybe a servo will make things easy for that plan of proportional. a stepper motor will also work. just the wiring and programing might not be as fun or easy.

off-topic. i love these threads(questions on whatever). just a really nice way to learn more by reading everyones replies and then learning where your own knowledge is wrong and getting new ideas, expanding on those ideas. its really inspiring!! :smiley:

10

Hello,

It is good to see yet another coming over to the side of technology, the dark side. :slight_smile:

If you just simply want on/off control of the motor, a relay would be an excellent idea. A relay is a simple device which allows a low power signal to switch a high power one. Imagine something like a washing machine. Say you want a guy who can’t move to turn it on. So the feeble guy commands a strong servant to go turn on the washing machine. The strong servant is a relay. They tend to be on the cheap side.

If, however, you want variable control of the motor (you want to be able to control the speed of the motor from your controller), you need to choose something else. I would recommend a darlington pair NPN transistor (79 cents at radio shack last I checked). The wiring for a transistor circuit will not be difficult, but it is kind of difficult to transcribe onto Chiefdelphi. (If anybody knows a way I can post a circuit diagram, please PM me). The transistor must switch the high power inputs with a low power control signal. I would connect the control pin of the transmitter to an analog output of the controller, the collector to the motor, then to the negative terminal of the +12V supply, and the emitter to the positive terminal.

11

If he’s using a FIRST controller with the default code, and he’s using a variable speed controller (victor) to control the motor, all he needs to do is connect the motor’s victor to pwms 13, 14, 15, or 16. These are, by default, the “drive” motors and are already programmed.

EDIT: To all the programmers out there, I’m not good with words, so what I was saying may not come accross as “correct” i.e. “the victors are already programmed”.

12

Wow! Thanks for all the replies! Perhaps a little background information on my project will allow for some more detailed advice:

I, along with two friends, are converting a full-size car (an '87 chevy nova) into a remote control car. The nova has an automatic transmission and power steering.

We need to work on 3 elements: 1) the gas, 2) the brakes, and 3) the steering.

For the gas, we have a small 5V servo hooked via PWM cables into the robot controller. This servo pulls the gas line, and works well; no troubles here!

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.

For the steering, we will again use a 12V motor. This motor needs to turn both directions.

We will most likely draw power from the car’s battery, possibly through the cigarette lighter outlet.

The robot controller we have is the FIRST robot controller from a few years back… perhaps the 2001 edition. I am not entirely certain. It has 5V output and 16 pins. It uses PBASIC.

My plan for the larger motors is to use victors. joystick forward will activate the servo on the gas line, joystick back will operate the 12V globe motor on the brakes, joystick left/right will operate the 12V globe motor working the steering wheel.

Does anything about this plan sound bad? Are there any glaring errors? Again, Thanks so much for your continued assistance!

ARP

EDIT: Oh, and our budget is minimal. The three of us pay for everything right out of our pockets, so cheap is good!

13

well, first of all, you were describing a whats called a rack and pinion for the breaks.

Next, If you are using that FIRST hardware, you are all set to go for 12V motors and speed controllers. The FIRST robot controller (FRC) outputs 5v to other things like speed controllers and victors that handle the 12V motors. The 5v circuit is just between the FRC and the controller while the 12V circuit is between the speed controller and motor. Just look at some of your schools robots and you will get the picture.

Im assuming you got the FIRST equipment for free, but if you really want to do it cheaply, you could probably get some electric RC hardware from a hobby shop or online, transmitter receiver, giganto-monster servo (at least RC plane-wise) and then two speed controllers to run the larger motors for steering and breaks all for like $200 ish

Sounds like a cool idea. Not so much for originality (its been done before) but because you sound like you are going to do it pretty simply and easily. Maybe i should try it out :slight_smile:

As for potential problems, a globe with the stock gear box almost defenitley does not have enough torque. Second, i’d be surprised if the servos you were talking about for the gas line had enough force, but if you tested it, i guess so.

Lastly, have a lot of fun, join your schools FIRST team, and… uhhh… have the letter ‘M’ stricken from the alphabet

14

WOW! i wish i could do something like that! if only i can get my hands on a car that actually runs thats REALLY cheap.
once you build it, how are you going to test it?? or actually, where?
if it goes out of control, thats really not a pretty picture…

ps. dont forget the hand brakes and shifting to neutral!! doing doing full 180s in drive at some speed will hurt your car… itll stall your engine if your going fast enuf :yikes:

and turning a steering wheel is kinda hard… and centering your wheels may be hard to program unless you have some sensors. yes they will eventually go staight but thats only eventually. itll take a lot of getting used to if youre gonna center your wheel just by pulling your joystick hopefully enough.

15

I would be very interested in talking to you about some things you might not have thought of I am involved with a project similar but a little more advanced if you check http://gcart.rit.edu you can see some of the things we have been working on for the first step of our DARPA car.

Some of the things I am concerned about your project:

Loss of radio - now this won’t be a terrible issue using the innovation first controllers but you don’t want one of the motors to keep going when you want them to stop so I would recommend a separate system of being able to “kill” the car remotely. There are a lot of ways to do this but it needs to be addressed

Motor meltdown - when it comes to FIRST robotics the use of motors from different walks of life is a fun challenge but when you are dealing with something so large scale you need the correct motor for the job. For breaking for instance I would recommend a linear actuator because that will much more reliable then the globe motor with a gearbox

Feedback - things like turning the car and speed need to be monitored during operation and I am afraid that if you don’t monitor it good control of the car can’t be achieved.

I am not bashing your project in fact I think that it is very cool and be very successful but I think there are a lot more issues that I think need to be addressed. cars can be dangerous things and proper control and preparations need to be made to ensure your safety and the safety of those people around where you operate this car…I would be glad to talk to you just drop me a PM on this board or Instant message me…

Also we defiantly want pictures when you are done!

Good luck with your project :smiley:

16

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.

17

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.

18

Just another heads up…

http://www.access.gpo.gov/nara/cfr/waisidx_03/49cfr571_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 :wink:

Good luck…

19

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

20

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!