Testing Replacement Dome Motor

Then new dome motor (a surplus Pittman GM9236) arrived today and I thought I’d share a short video to compare it to the original underpowered GM9413 motor I had been using.

It’s still runs at 12V, so no need to upgrade my electrical system to 24V. It spins a lot faster and definitely has a lot more torque.

Here’s the original GM9413 for comparison.

And finally, here’s a quick side by side shot of the two motors, the GM9236 is on the left. It’s a little bit longer and has a small shaft at the bottom which I think is to connect an encoding wheel to.

Posted by Chris on December 17th, 2007 in Dome, Electronics | 2 Comments

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New Pittman Dome Motor Ordered

Pittman GM9236I’ve continued to do research and testing on my dome drive system, and it does look like I need to change the motor out for something with a bit more humph.

It seem that a few people are happy with driving the recommended GM9413 Pittman motor at 24V instead of 12V with good results, but I really want to avoid introducing the complexity of 24V into my system just for one motor. It will complicate charging the batteries at best and the shorten the system run time between charges, and at worse reduce the overall battery life unnecessarily.

In the last day or so I’ve got a lot of great advice from fellow builders, including a lot of links that helped me decide which new motor to go with. I wanted to stay with a Pittman if I could to hopefully avoid redesigning the dome drive system, and it looks like one of the variations of the Pittman GM9236 would work. It comes in a few different gearings and voltage ratings.

There was one specific 12V version I was shopping around for, the GM2936S018, which delivers about 3 times the torque, and about twice the RPMs of my current motor, but it was around $130, and I’d rather find something a little cheaper if I could. Then Bob pointed me at another GM9236 model that was very similar, but only $23 at a surplus store. They’re used/surplus but probably worth the risk so I ordered one to try. It has very similar specs delivering a lot more torque and hopefully went it’s installed, spin the dome a little faster 🙂

So here’s the links I used for my research and where to find motors

Posted by Chris on December 7th, 2007 in Dome, Electronics | No Comments

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Dome Drive – Possible 24V Solution

It does look like I may end up trying running the Pittman Dome Motor at 24 volts as a test going forward. I can’t see adding a gear at this point in time.

This leads me to my next problem, my battery sub-system is all 12 volts. I’ve had no need for 24 volts in the body as my main drive motors the NPC-2212’s can only run at 12 volts, and everything else is stepped down from 12 volts using Dan’s distribution board.

I know how easy it is to create 24 volts from two 12 volt batteries, which I have and can do with what I have on hand, but configuring in series and then tapping off for 12 volts adds a level of complexity for charging the batteries w/o removing or rewiring each time. There’s also the problem of one battery draining faster.

For those unfamiliar with creating 24 volt from 12 volt batteries, this is a really good site explaining how and some of the problems.

One of the problems he talks about is charging unbalanced batteries in parallel and something called a “Battery Equalizers / Balancers” which can fix this problem. The unbalance comes from the 12 volt tap on a 24 volt system, and the two batteries discharging at different rates.

I’m hoping someone has tried an equalizer in their droid before. I’ve found a lot of information on equalizers, mostly large clunky boxes for RV’s and buses, but there are smaller version out the like this one.

What I’m hoping is to use the 3 12 volt 7amp batteries I’m using right now in parallel, and then combine two of these in series for 24 volts. For charging have a switch/circuit to disconnect/isolate them from anything in the droid and reconfigure just in the parallel state to charge all 3 batteries together.

Tall order I know without causing a short circuit or fire 🙂

Posted by Chris on December 5th, 2007 in Electronics | No Comments

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