Feed back pots

[Bruceaust]

I have questions regarding feedback pots for a 2DF joyrider.

I have read that pots between 10K and 100K K will work.
Q1. What is the optimum resistence variation from the travel end point to end point?

My wiper motors rotate about 720 deg end point to end point.
This means I will need to use multiturn pots connected directly OR use gearing to rotate the pots more.
Q2. Can I use a 10 turn pot and only use 2 turns of its range?

I think you can see what I am getting at here. If I know the optimum "resistance span" ( 0 to "x" K) , it would be simple to
use a pot that gives the correct range from travel end point to end point - without the need for gearing to drive the pot.

Thanks for any advice.

(I am getting close to finishing my project should I re-post my project form the old Xsim site?)

[motiondave]

Hello, with your wipers, are you using a pulley set up? I'd guess you are if it is 720 deg rotation, as one turn is 360 deg.
Best you use multiturns, but have a look around for gearing , as the size of the gearing will help determine the turns on the pot.
What I mean is, for example, I use 5 turn pots on mine as the gears give me about 3.5 turns. So if you find gearing to suit a 10 turn, then use that.
Also a 5-10k ohm linear pot should do. Either is fine.
But someone please correct me on their setup.

[Bruceaust]

Thanks for the reply, I guess I am just trying to simplify things by not having to use gearing

[motiondave]

You may be better getting a single turn mounted on the frame somewhere, so the pot "reads" off the frame and not the motor.

I did this with my first frame, look at the right hand side of the photo.
I since moved to motor mounted pots after that, but the first setup worked very well.

[tronicgr]

(I am getting close to finishing my project should I re-post my project form the old Xsim site?)

Of course you can and you should re-post your project here. The old x-sim3 forum will be there for limited time to give people a chance to copy their projects.

[Bruceaust]

Thanks fellas, I will post my project shortly. I have made significant progress ( nearly ready for the smoke test! ), just need to install feedback pots.
This is a bit difficult on my design. I am investigating modifying the back of the wiper motor so that the pot is directly driven from the rear of the final output gear. I saw this somewhere and will see if it can be done in my situation.

[motiondave]

Pot on back of the motor will work, just remember, single turns only go 270 deg, while a motors goes 360 deg. If you motor overshoots its mark and spins over, it may trash the pot. But usually single turns are $3-$5 each.
Sort the pot issue out before going to expensive multiturns, just a suggestion.

[Bruceaust]

Yeah, I have ordered some 10K 3 turn pots from ebay. My motors only rotate 2 1/2 turns between endpoints so that gives me a little bit of safety margin.
I also plan to put limit switches on each axis that removes supply to the AMC. I know this is not as good as cutting DC supply to the motors, but finding limit switches that can switch a large DC current is not easy. Another more sensible option might be to use car starter solinoids driven by small limit switches. This would isolate the supply to everything.

[CraCk]

Someone had experience with this sensor?
http://www.automation.com/content/bi-te ... -rotations

[Bruceaust]

Thanks crack,

I have seen those, they look great but they are very esxpensive.
I have just ordered some hall sensors and magnets to do the DIY thing.

Something similar ( but quite different!) to : http://www.simpits.org/geneb/?p=299

I will see how it goes and post my efforts.