I have what will be a stupid simple project for all of you, but even the simplest of robotics controll systems are a mystery to me. The mechanical aspect I have down. I need to know how make a low voltage motor start and stop in the same position (precicely) after a single rotation. The type of motor will be determined by what I need for the project ie stepper motor, induction or standard. Speed controll is a must. One cycle = one rotatoin over a two to ten second period. This is of course acheavable thru a small gear train but direct drive is preferable for simplicity’s sake (fewer moving parts, greater reliability) the cycle needs to be triggered by a single low voltage pulse from say, an arcade switch. The system needs to be simple and reliable. Any thoughts?
Rotation Questions
Questions:
1. How do you know the home or zero point?
2. How much torque do you need?
3. What exactly is precice to you?
You have a number of
You have a number of options.
You can go with a servo, a motor with encoders, a motor driver and a controller or if accuracy isn’t imperative, you could have a motor which will hit a switch every time it goes around the circle.
To get a motor that will do 6- 30 rpm, you will need to have it geared. Picking a motor is a difficult task since you haven’t said what you need for torque or what if anything the motor will have to turn. That information will greatly influence exactly what motor and/or motor driver you choose.
Regards,
Bill
Total newbie,Ok, I should
Total newbie,Ok, I should have been a bit more specific, sorry about that. This application is basicaly a music box, but bigger,the motors job will be to turn a cam that in turn will actuate a set of hammers (4) that will ride up on the cam lobes until they fall past and strike a bell. The cam will weigh under a pound and each hammer about six ounces. I haven’t done any calculations wih reguards to a gear train but that is easy enough to figure, but 3 lb. ft.of torque at the final drive for this application should actually be over kill. Accuracy is important, because if the motor stops even a fraction of a degree early OR late eventually the cycle will begin or end in the middle of the song. The cycle MUST be accurate and repetable/reliable. Packaging is not a huge issue so I can use as large a motor as nessessarry. As far as the home or zero point is concerned, I can set the cam timing based on motor position. And to what is precice to me, that would be 360 deg. Unless a reset function could be built in to the system in which case +/- 5deg would be acceptable
Total newbie,By Chopper35nj
Total newbie,By Chopper35nj @ Fri, 2016-01-15 20:16
Total newbie,Ok, I should new
edit reply Report Spam You can’t chill your own stuff 
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Total newbie,Ok, I should have been a bit more specific, sorry about that. This application is basicaly a music box, but bigger,the motors job will be to turn a cam that in turn will actuate a set of hammers (4) that will ride up on the cam lobes until they fall past and strike a bell. The cam will weigh under a pound and each hammer about six ounces. I haven’t done any calculations wih reguards to a gear train but that is easy enough to figure, but 3 lb. ft.of torque at the final drive for this application should actually be over kill. Accuracy is important, because if the motor stops even a fraction of a degree early OR late eventually the cycle will begin or end in the middle of the song. The cycle MUST be accurate and repetable/reliable. Packaging is not a huge issue so I can use as large a motor as nessessarry. As far as the home or zero point is concerned, I can set the cam timing based on motor position. And to what is precice to me, that would be 360 deg. Unless a reset function could be built in to the system in which case +/- 5deg would be acceptable
Total newbie,otal newbie,Ok,
Total newbie,otal newbie,Ok, I should have been a bit more specific, sorry about that. This application is basicaly a music box, but bigger,the motors job will be to turn a cam that in turn will actuate a set of hammers (4) that will ride up on the cam lobes until they fall past and strike a bell. The cam will weigh under a pound and each hammer about six ounces. I haven’t done any calculations wih reguards to a gear train but that is easy enough to figure, but 3 lb. ft.of torque at the final drive for this application should actually be over kill. Accuracy is important, because if the motor stops even a fraction of a degree early OR late eventually the cycle will begin or end in the middle of the song. The cycle MUST be accurate and repetable/reliable. Packaging is not a huge issue so I can use as large a motor as nessessarry. As far as the home or zero point is concerned, I can set the cam timing based on motor position. And to what is precice to me, that would be 360 deg. Unless a reset function could be built in to the system in which case +/- 5deg would be acceptable
Total newbie, LOL, this
Total newbie, LOL, this forum works a lot different than the others that I have been involved with. Sorry for the multiple posting of the same reply.
Ok, that narrows it down
Ok, that narrows it down some more. There are a lot of ways to do this. You could use stops like a music box or have a cam hit a limit switch that starts and stops the motor. Probably something like that would be accurate enough for what you are trying to do. You don’t talk about wanting to do multiple songs, so this could be done that way and not delve into the digital world.
www.servocity.com has a number of motors that will give you around 30 rpm and meet your 3 ft/lb torque requirement.
https://www.servocity.com/html/32_rpm_hd_precision_planetary_.html#.VppmISorKM8
Since I know how to code, I would use the above motor with an encoder like this
https://www.servocity.com/html/32_rpm_hd_planetary_gear_motor.html#.VppfeCorKM8
will give you about 16 ft/lb torque so more than enough.
I would use an Arduino ($10-20), a motor driver ($15) and write code to control it. You will have a lot more control, be able to possibly do multiple songs etc. It will be some learning curve though since you will need to write some code to do this. If you are interested in that approach, there is lots of code available on how to do that online. I also have done something similar (I can send a command to my robot and have it go precisely 1 m or so many degrees when it turns) but it is difficult to follow. If you are interested in this approach, I can remove some of the harder to read elements and post it for you with some explanations. It will be a start. Others might find it interesting.
Regards,
Bill
That’s a job for a geared
That’s a job for a geared stepper nema17 or a 12v dc motor with encoders, medium size. A geared stepper has more torque at low speed, and is able to move with 1.8° each step. You can either get a geared stepper or get a normal stepper and 3d print/ cut gears as needed.