Powering a Larger Motor?

[arpus maximus]

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 (arpus_maximus@hotmail.com) or just post here.

Thanks in advance,
ARP

[Ryan F.]

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.

[Greg Needel]

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

[greencactus3]

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
http://science.howstuffworks.com/inside-transformer.htm
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.

[Greg Needel]

Originally Posted by greencactus3

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).

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

[greencactus3]

Originally Posted by Greg Needel

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

sorry.. may i ask what a relay is??

[Andy A.]

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.

[Greg Needel]

Originally Posted by greencactus3

sorry.. may i ask what a relay is??

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

[greencactus3]

Originally Posted by Greg Needel

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

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!!

[Venkatesh]

Hello,

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

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.

[Joshua May]

Originally Posted by rforystek

As for the programming...I'm not the person to ask.

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".

[arpus maximus]

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!

[Max Lobovsky]

Originally Posted by arpus maximus

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!

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

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

[greencactus3]

Originally Posted by arpus maximus

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.

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

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.

[Greg Needel]

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