The secret is to look at the Render menu at the top right of the canvas. Turn off everything you don't really need for the task at the moment. If you're using lights, and are now working on cameras, turn off the lights. In the Resolution section of that menu, turn off Dynamic, set it to Half or Qurter. Set the Quality to Normal or even Draft.
When you're done, you can turn these all back on in the Render menu there, or override that in the Export dialogo box, where you can set them.
One technical spec that you didn't list is your display RAM. I think the i3 iMac came with a 256Mb or 512Mb display card.
So, while more RAM might help, more display RAM is what you're after. The i5 and i7 2010 models had a 1GB option (if I remember correctly, it was a build to order option and not an upgrade).
If you anticipate a lot of Motion work, you might price a new iMac with i5 (or i7 upgrade) with the "Configurable to NVIDIA GeForce GTX 680MX with 2GB of GDDR5 memory." It adds $150 to the price, but you should appreciate the boost in GPU while working in Motion.
Also, a key to working faster is everything that BenB suggested. So, you can work quickly and then wait when you are ready to export.
And, yes, you can cram 32GB of RAM into the 2010 models. Be sure to buy it from OWC so you have technical support. Keep your original RAM, though. If you still have AppleCare and call Apple, there is a chance they will ask you to put the original RAM back in for troubleshooting (I've dealt with this back in the days the mirror door G4 was still around and had to go back to the orignal ram spec rather than what I had upgraded to). And again, more RAM isn't really going to get you the performace boost you're looking for.
plus I have tried updating my iMac with more RAM
1. I bought RAM from OWC and had to pay tax to get the RAM into Spain, OWN seems to be twice the price of anyone else
anyway my iMAc mid 2010 i3 27inch would not take the upgrade
2. I tried Crucial 32gb RAM 8gb each slot and again the iMac refused to take the RAM so I sent both lots of RAM back to the sender
I bought the Crucial RAM through Amazon
any ideas what I am doing wrong, is there a type of RAM I need?
Are you just trying to get Motion to work in the first place? Or,
Are you trying to get Motion to work faster?
If you're trying to get Motion to work faster, more RAM isn't going to do what you're hoping for. Either Motion has enough RAM to render the scene or not.
When it comes to speed performance in Motion, it's GPU that matters followed by CPU.
Your iMac probably has the following graphics card:
ATI Radeon HD 5670 graphics processor with 512MB of GDDR3 memory
In and of itself, that's a good graphics card; however, if you feel that Motion should be faster, then you need the "512Mb" to be "1GB" or "2GB" instead. You're probably already aware that this isn't something that you can upgrade with an iMac.
It's unfortunate that the two 16GB sticks that your ordered are not working. More RAM rarely hurts anything. But even if you install two 8GB sticks for 16GB total, you're not going to see much of an imrpovement in speed.