| Author |
Message |
Peter
Unregistered guest
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| Posted on Thursday, December 27, 2007 - 11:57 am: |
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Could I please ask for your advice on product selection. I want to fit a drive to a mirror on an astronomical device such that, from a known
start position (nominal zero), I can rotate the mirror to a pre-determined angular position. Maximum rotation from zero would be approx 90 degrees. The drive would be fitted on the axis of rotation and the load is well balanced so there would be minimal torque required. I would like to be able to calibrate / set the zero position
and then rotate the mirror to the desired angular position by,say, entering the angle required using thumb wheel switches or similar.
The motor which would seem to "fit the bill" is EMG30 Geared Motor 4.22W with Encoder but I am not sure how I could obtain the control method that I want.
Your help would be greatly appreciated.
(I am assuming that my e-mail address will not be posted on your web site. Please withhold.) |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 652
Registered: 10-2004
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| Posted on Thursday, December 27, 2007 - 9:22 pm: |
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Peter,
You did not leave an Email address so hopefully you will spot the reply.
There is at least three ways of doing this, a motor with encoder, a servo or a stepper motor. We currently do not supply stepper motors but as the other two methods will work, I will focus on them.
The EMG30 has a rather high rotational speed for your application at 3 revs / second which is only about 80mS to move the full 90 degress. Probably too quick for your application.
A standard type of radio control servo can rotate the 90 degrees, many sizes are available with different torques, some even have coreless motors for quick response or digital control for accuracy. Which ever one is selected, all you need to do is generate a pulse train that is compatable with a servo.
So, the main challenge is generating the correct pulses. As you do not need PC control, the method really depends on your experience with electronics and / or programming. A relatively easy electronics circuit could be designed or use one of our PICAXE controllers with some simple software.
What is your electronics knowledge like? |
Peter Cowley (Stargazer)
Member
Username: Stargazer
Post Number: 1
Registered: 1-2008
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| Posted on Wednesday, January 2, 2008 - 11:56 pm: |
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Thanks for your reply and apologies for not getting back to you sooner. My electronics knowledge was good 40 years ago!! Now I could assemble a controller but could not design from scratch. I was hoping to find an off-the-shelf solution.
The EMG30 would be much too fast. I like the idea of using a standard RC servo. Any ideas where I could find a suitable contoller or circuit diagram?
Thanks for your help.
By the way, I probably didn't leave my e-mail address as I wasn't sure whether or not it would be posted in the forum (which I don't want). Anyway, I have now registered so hopefully you will be able to see my return address. |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 654
Registered: 10-2004
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| Posted on Thursday, January 3, 2008 - 7:28 pm: |
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Peter,
We have change the automatic preference so that registered users do not have their Email address shown on new posts. However, we have access to them as an admin users so we will send you a personal reply as well.
I am not aware of any purpose made modules or circuits but all you need is one of our PICAXE starter kits 3803-001 and a 3803-100 chip plus some very simple programming. So for about £12, you get the circuit board, all components, a disc for the software to run on your PC and a programming lead. If you need help with the actual BASIC programme, just post here once you have installed the software and we will talk you through it.
Regards
Paul |
Eric Parsonage (Lamestllama)
Member
Username: Lamestllama
Post Number: 1
Registered: 9-2008
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| Posted on Saturday, September 6, 2008 - 4:35 pm: |
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Hi
I just recieved my 5th MD23 and have a problem that it stops responding to i2c after a few seconds.
I have 2 robots each with two md23s in them. Both robots have the same issue with this new MD23 installed but neither have problem with the old MD23s installed. In addition and this may be some sort of clue. If I disconnect the motors (and encoders) from the suspect MD23 then there is no problem (except of course the motors wont go round) This is the same in both robots.
I was wondering if there has been any software revisions in the last few months ? I know I could write some code to find out if they had different software versions but I know from past experiment that all 4 of the previous ones where rev 2.
Looking forward to hearing from you.
Regards
Eric |
Admin (Admin)
Board Administrator
Username: Admin
Post Number: 869
Registered: 10-2004
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| Posted on Saturday, September 6, 2008 - 7:17 pm: |
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Eric,
Could you quote us the last 4 digits of the each invoice (it's the same as the order confirmation number as well) you purchased these controllers on. Email them to sales(at)technobots(.)co(.)uk if you prefer and we will investigate. |
