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I Need an RC Mentor!

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Old 02-28-2014, 11:16 AM
  #1
Megs
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Question I Need an RC Mentor!

Hello everyone,

Glad to have found this forum. I've got a project going that doesn't really fit into the realm of "RC" but will most likely use all RC/Hobby type and size parts. My knowledge of this world is fairly limited and I would love some help from those of you that know this stuff like the back of your hand!

You see, I'm trying to get a motor (a small one, maybe brush-less?) to turn a small wheel/pulley (less than 5" in diameter) at a max speed of less than 20mph. The speed and direction would ideally be variable... remote control would be awesome!

On the topic of motors. If the pulley is over-loaded (ie if you stop it from turning by force) I'd rather if the motor didn't burn up. Am I right in thinking that this would be ok with a brushless motor? Am I totally missing something here?

From what I can gather, this is fairly low RPM (about 1300 I think) in the world of rc motors. That's ok, because I need a decent amount of torque. There are ways to get a higher RPM motor to turn more slowly and thereby produce more torque, right?

Also, I'd like to talk about batteries and battery life. Ideally, I could run this pulley for about 10 minutes before needing to recharge.

Lastly (and here's the part where you might have to laugh at me!) I'd like to put this contraption together for about $100.


So here are my (probably very silly) questions:
  • Am I totally off-track?
  • Can you get me on the right track?
  • What do I need? (list of components)
  • What kind of motor/ motor configuration would be best?
  • How would I best put this together?

You see, I've made a really simple prototype but I'm stuck when it comes to getting it to operate the way I want (I'm touching wires together to make it go and clamping the thing together!) I also tried using a slot car controller, which works ok for this motor as far as varying speed, but wouldn't be useful for a brushless version. Lastly, the current prototype can't easily change direction. I need a switch or something in the next one to be able to do this. I'd appreciate any and all advice and thanks in advance!

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Old 02-28-2014, 11:29 AM
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Hi Meg ,

If this is a school project or something , it would be helpful to know the exact description of what this is intended to do . Lifting something ? Reeling back in a cast fishing line/lure , or an automatic dog walker ? (Or perhaps an automatic cat strangler , KIDDING , Just kidding ) .... But seriously , knowing the end use will be critical to receiving the best targeted answers
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Old 02-28-2014, 11:33 AM
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Yes yes, sorry!

It's a toy. It will run a small line (like a clothesline) around so you can attach stuff to it... come to think of it, cat-strangler might be another use (ok, also KIDDING!). But it could be a toy for a cat if you put feathers on it

Video may help, let me try to upload it.
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Old 02-28-2014, 11:38 AM
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Default Video of Prototype

So here's the really rough prototype in a video (hopefully)

http://youtu.be/pssSVBjoUmk
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Old 02-28-2014, 11:45 AM
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you seem to be on the right track, Megs.. there only ONE thing that jumps out at me from your original post...
if the motor is overloaded / stopped by force.
a brushless motor is not going to help there... there would need to be something programmed to shut the motor off if it is physically stopped.
(something to monitor the current to the motor which would stop it IF the current gets too high.)
the same goes for a brushed motor.
incidentally, you'll find a wealth of Mentors here you're in the right place.
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Old 02-28-2014, 11:51 AM
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Thanks, I know I'm missing pieces of the puzzle. So would this thing be mechanical (like a clutch) or would it be easier to do the programming? And how to program, what gets programed- the motor controller? Are there ones available with such a feature or is this a custom job?
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Old 02-28-2014, 11:52 AM
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Wow , nice work on the prototype ! It looks like what you really need at this point is just a speed controller for your motor , yes ? You mention brushless , which would be a great way to go but if the motor your presently using is brushed there are speed controllers for those as well . Now , any speed controller (called an "ESC" by RC folks , for Electronic Speed Control) for model plane use will be useless to you as us plane guys don't have reversing built in to our ESCs .. Not to worry though , the guys who run RC cars got ya covered , cause RC car ESCs most certainly do support forward/reverse . A possible idea here may be , since we're doing this the inexpensive route , to get a RC car and scavenge it's electronics and maybe even it's motor too if it will work in your design .

Kudos for your inventive spirit !
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Old 02-28-2014, 12:03 PM
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I think init4fun has the right idea... RC cars do work the way you're looking to make your project work...

what popped into my mind originally is the way that "servoless electric retractable landing gear" work..

but those are not adjustable or programmable
most likely the car forum guys would be able to help better that I.
nice prototype work!
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Old 02-28-2014, 12:21 PM
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Quote:
Originally Posted by init4fun View Post
Wow , nice work on the prototype ! It looks like what you really need at this point is just a speed controller for your motor , yes ? You mention brushless , which would be a great way to go but if the motor your presently using is brushed there are speed controllers for those as well . Now , any speed controller (called an "ESC" by RC folks , for Electronic Speed Control) for model plane use will be useless to you as us plane guys don't have reversing built in to our ESCs .. Not to worry though , the guys who run RC cars got ya covered , cause RC car ESCs most certainly do support forward/reverse . A possible idea here may be , since we're doing this the inexpensive route , to get a RC car and scavenge it's electronics and maybe even it's motor too if it will work in your design .

Kudos for your inventive spirit !
Yeah and the RC car ESC's even have a brake function that can be programmed. I would recommned brushless for this since they have far better torque and braking efficiency than brushed motors. Also, you can get a car system cheap incluting the transmitter (controller) if you look in the classified section here on RCU and probably on Wattflyer also.
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Old 02-28-2014, 12:34 PM
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Thank you!

So an RC Car ESC would be what I'm looking for.

Any ideas on how to stop the motor if the current gets too high (in an overload situation?) I'm still totally in the dark on this.
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Old 02-28-2014, 12:41 PM
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probably the simplest way (although perhaps not the most elegant)
would be to have the motor drive the pulley via a belt, with the belt loose enough that it would slip if anything got hung up.
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Old 02-28-2014, 12:45 PM
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Or just put a good old fashioned fuse in the circuit. You can use an automotive fuse, they can be had for next to nothing at any auto parts store.
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Old 02-28-2014, 12:51 PM
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Hmmm I really like the belt idea, a fuse would be a one-time thing right? If it bows you replace it.

I guess the belt would be replaceable as well, but would probably last longer in the event of overload.

Also, maybe my "belt" could be a rubber band. I've got lots of those!
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Old 02-28-2014, 01:54 PM
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You could get a circuit breaker vice a fuse. a C/B is not a one time use but will limit the current. It would also be a bit easier than a belt. A belt could work but if its too tight you burn the motor and esc if too loose then it slips all the time. also with reversing I can see the belt getting thrown. I would go with a DC circuit breaker. I would get the amp spoec for the motor and the ESC and then get a breaker at the lower of those 2 specs.
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Old 02-28-2014, 04:44 PM
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A mechanical clutch seems to be the better solution here. There might be some high end controllers which you set a max current limit, but they'd probably out of the budget. You can use a time delay fuse or circuit breaker, but it doesn't seem practical here.

Now the motor/esc selection depends on the load, speed and acceleration ramps.
You can control the esc with a 'servo tester' - an inexpensive device, like this here:

http://www.hobbyking.com/hobbyking/s...h=servo+tester

You'll find everything you need on that website, or www.valuehobby.com since Hobbyking is in China and shipping takes a few weeks.

If you have an outlet close by, I'd just use a DC power supply, so I don't need to worry about charging a battery.
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Old 02-28-2014, 05:19 PM
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I only see 2 wires from the motor which tells me its a brushed motor and since it works fine then keep it. Brushed speed controllers are alot cheaper these days since brushless is the next big thing. I raced electric cars for 7 years and alltho reverse was illegal to use racing it was common in alot of cars just for fun and the convenience of not having to chase after the car if u got stuck lol. What u would need is a trasmitter either stick or pistol grip (commonly used for cars) and there would be advantages to both. In this set up i personaaly would prefer a stick type controller for several reasons. 1) if you centered your throttle stick and had an esc with reverse then you could control how fast and which direction the line went . 2) once you set the stick at the right speed you could go completely hands off and let it go. you would also need a 1 or 2 channel reciever ( go with a 2 channel eaasier to find and same price. you would also need nicad batteries. Since the invention of lipo batteries also the next big thing these should be cheap as well so. With a cheap transmitter, cheap speed control, reciever and cheaps batteries it would most likely be a cheaper way to go. If you really wanted a clutch assembly you would only need a few pieces from a pan car like a 10L . you would need an axle (for a pan car) 2 differential rings a spur gear ( large gear on the axle) some small differential balls and light grease. and a smaller pinion gear for the motor. You would also need 2 bearings and bearing holders. It may sound like alot but it isnt. If the motor started to fast the differential would slip a bit depending on how much you tightened or loosened it so you wouldnt have to worry about overamping your motor or speed control. look at atem #966942 and ofer the guy 20 bucks for either radio and reciever shipped and the radio part is done. I dont know the guy im just saying for 20-25 you could have the raqdio and reciever. item 966914 in radio equptment is asking 40 + shipping for a reversible esc i dont know him either but id see if hed take 20-25 shipped. if it were me id buy the radio and esc and a battery or 2 and leav it at that. Also if you clever enough you can probably find a cheap radio shack car and get most everyhting you need in 1 stop. You dont need fancy i end stuff cuz if anyhting goes wrong u can just pull the plug lol. In fact now that i said that i would really try that. its highly possible you could buy a cheap rc car that goes fwd and reverse. Take the body off take the wheels off( leave the hub if it helps you mount it to your pulley) mount the drive axle to you pully and operate the whole thing the same as you would the car with everything built for you and all that you would need to do is figure out how to mount your pulley to the drivetrain. try radio shack toys r us wallymart and look for a cheap car or truck that does what u want and your good to go. Alot of choices. didnt mean to get windy but though of the cheap rc car thing afterwards lol. good luck with the project . Let us know how it turns out. Gary
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Old 02-28-2014, 05:21 PM
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What I would do, would be hook up a brushed motor straight to an RC battery. Then, watch, and pull apart if something goes wrong. That idea is just me thinking....
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Old 02-28-2014, 08:53 PM
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Quote:
Originally Posted by Megs View Post
Thanks, I know I'm missing pieces of the puzzle. So would this thing be mechanical (like a clutch) or would it be easier to do the programming? And how to program, what gets programed- the motor controller? Are there ones available with such a feature or is this a custom job?
Megs, I have a good friend who lives in your area. I'm sure he would help you. PM me if you need any help.
Best of luck!
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Old 03-01-2014, 04:56 AM
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servocity.com has a lot of neat stuff for projects like this ... reversing speed controllers, gear reduction motors, pulleys, belts, etc... . It is more expensive than hobbyking, but they are more likely to have something to meet your needs. Good people to work with too.
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Old 03-01-2014, 07:13 AM
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A belt tensioning pulley arm laying on a micro switch in the throttle circuit would kill the circuit if it came off the switch. Too much line tension would overcome the arm spring tension and activate the switch.
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Old 03-01-2014, 08:16 AM
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There's no reason to go brushless on this project. You'll spend considerably more money with no real benefits aside from better energy efficiency. With a brushed motor, unless you need to be able to throttle it down, you can go directly into the battery and set up a simple reversing switch to get the pulley to go both ways. No speed controller is required for a brushed motor unless you need to be able to control the speed.
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Old 03-02-2014, 06:41 AM
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Quote:
Originally Posted by OliverJacob View Post
A mechanical clutch seems to be the better solution here. There might be some high end controllers which you set a max current limit, but they'd probably out of the budget. You can use a time delay fuse or circuit breaker, but it doesn't seem practical here.
Ok, so the belt idea might not be the most elegant solution. I like the idea of a mechanical clutch but was having trouble coming up with how it might work. Will definitely dig into this idea more.

Quote:
Originally Posted by redskyhawk View Post
servocity.com has a lot of neat stuff for projects like this ... reversing speed controllers, gear reduction motors, pulleys, belts, etc... . It is more expensive than hobbyking, but they are more likely to have something to meet your needs. Good people to work with too.
Reversing speed controller sounds like exactly what I need!

Also, I'm not married to my current motor, although it has been useful for testing!
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Old 03-02-2014, 09:01 AM
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I am thinking of something like this:

http://www.ebay.com/itm/Traxxas-Slip...item2a38657259
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Old 03-02-2014, 09:06 AM
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I am sure someone here has a lathe and could make an adapter for your motor and the pulley.

If you want to keep it simple, a brushed motor will work fine. If you ask some car guys, I am sure someone has a motor and reversing speed controller laying around and will sell it for cheap :-).
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Old 03-02-2014, 01:51 PM
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How fast do you want to make this go. A automotive type window regulator would be plenty strong enough with the gear box but would be much slower and it being a 12 volt DC brushed motor should be easily reversible.

Dennis
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