CarBEN Model -- 1/24th scale model and 3D computer model for EV - Page 34 - Fuel Economy, Hypermiling, EcoModding News and Forum

NeilBlanchard · 02-17-2012, 11:38 PM

Yes, the Volvo is similar, or vis versa. The main difference is the rear wheel track on CarBEN EV5 is about 7" narrower than the front wheels. And the underside of the rear bumper has a crisp trailing edge.

straight5 · 04-19-2012, 03:45 PM

any updates?

NeilBlanchard · 04-19-2012, 03:53 PM

I am nearly done drafting the 2" thick sections -- I am on #40 on the rear; having done the 38 section in the front. I have just 12 sections left to go!

Then I'll know an exact count for the number of sheets of foam I need to order (looks like it will be about ninety two 1" thick sheets of Dow XPS), and then I can get going on cutting them. That still means there is a fair bit of computer work -- the sheet layouts have to go back into SketchUp and and edited to then generate the g-code for each.

SubSonic · 04-20-2012, 05:19 PM

I have to admire your commitment and dedication to this project, but I am also bemused and flabbergasted that you have not done any testing towards your Cd goals? I may be incorrect in saying that as I simple did not read all of your posts - did you get a parasolid model in the end ( .igs .stp. .sld etc) and flow analyse it?

If you did not then I have a proposition for you (purely because of your effort). If you do have a solid model or surface model (not poly mesh, .stl, .obj, .3ds, etc) I will do you a flow analyse. However in return you must calculate the reynolds numbers required for your scale of model and it velocity for the test in advance. Sorry being a lecturer I can't help myself doing such things.

Also please do not be to put out if your expectations are not what what you think.

regards

SubSonic

NeilBlanchard · 04-20-2012, 11:57 PM

I tried several times to do CFD. The problem is my SketchUp model is very "leaky" -- no surprise, really. And it is very rough, too. I am still hoping to remake the model with the very much smoother sections. I do hope to get at least a rough idea of the Cd.

Another option is to build a quarter scale model and take it to the MIT wind tunnel. Or, measure the actual car in coast down tests...

SubSonic · 04-21-2012, 06:09 AM

To fix a 'leaky' mesh as you put it you can use a free tool called Netfabb (can't add links yet as I'm only at 4 posts) which is excellent at modifying/fixing such problems. Downside to this is the model will still be a ploy mesh and not a solid or surface, which is what you would require for any CFD work.

The other alternative if you are a student is to download Solidwork education, by simply registering. They allow students to use the software for a year at a very small price. This option would actually allow you to conduct flow simulations yourself.

A colleage of mine has mentioned a open source application that allows meshed models to be converted in solids and then simulated for FEA. If I remember correctly it was called 'Aurora Z88'? I have not investegated this source yet. However this may allow to convert your model.

kind regards

SubSonic

NeilBlanchard · 04-21-2012, 08:33 AM

It's more than the leaks -- the surface is heavily tessellated and it is definitely not smooth. The renderings smooth out most of these, but there are areas where even then, you can still see the roughness.

The most important thing right now is to build a chassis. There are many things to work out and the best / only way is to work on the real thing. I can do real world tuft testing -- either way, I need to finish the drafting work on the sections, and then order the foam and get my CNC machine humming...

SubSonic · 04-21-2012, 11:01 AM

As you wish...

If you change your mind just let me know, as I have powerful workstations for flow analysis at my disposal.

good luck

SubSonic

NeilBlanchard · 04-21-2012, 04:44 PM

Right, I appreciate the offer. I do hope to make a smooth tight model, but the physical thing has to come first, to work out the various design issues, and to show real world progress; which is the only way to get more people interested.

NeilBlanchard · 04-23-2012, 12:25 PM

I have completed ALL the drafting on CarBEN EV5!

Woohoo! There are 49 sheet layouts, and 5 of those are 1" thick, so that means I need a minimum of 93 sheets of foam. I need to export them into SketchUp and process them to then generate the G-code to cut the sheets in my CNC machine!