Henry: A very much appreciated piece of writing! Right, point by point:
> Date: Wed, 25 Nov 2009 05:57:23 -0800 > Subject: [TANKS] Re: Complete Newbie... > From: [email protected] > To: [email protected] > > A few thoughts: > > 1. It would be interesting to see an 8-wheel model. I agree they are > cool, regardless of suitability for paintball. I am surprised that no > one among the manufacturers of large scale RC tanks is offering a > model of the Stryker, given the number of people who have served in > that vehicle. I would think there is a market among vets for such a > toy. The only 8-wheel AC model I have seen is the WWII German Puma, > made by that Russian guy. You're very correct in that there just isn't much out there. I've seen the SdKfz 234/2 you're talking about, and at over $2,000 a pop... Yea... Thanks, but no thanks. However... that very model was exactly what got me interested in building one of these. I remember thinking that was easily the sleekest, and coolest looking fighting vehicle I had ever seen, and wondered why no one had ever combined the mechanical simplicity of a wheeled vehicle with a big anti-tank gun: vuala! The Rooikat/B1/Stryker MGS, etc. There just don't seem to be be very many of them. > 2. Before I got diverted into building a robot, I thought about > building an AC. I wound up building a couple of 4wd vehicles, which > were not scale models of anything. I thought about an 8wd, and > basically came up with a similar design you have: use large scale rock > crawler parts. The catch was cost. However you seem to have more > skills in scrounging. > Hardly "skills": it comes more from being a tightwad and having planned (if such a word exists in my vocabulary) large portions of this project before ever even beginning. I had looked at going all RC Crawler parts, but they seem to be exclusively solid axle: excellent for building jeeps, trucks, etc. But I love scale. and the idea of trying to spring 4 solid axles with anything resembling a workable suspension system capable of any speed/off roading gave my headaches even more headaches. So, I decided to go with independent, and was looking at trying to build my own swing arms out of electrical conduit, copper plumbing pipe, PVC pipe, cut and shaped sheet metal, and the list goes on and on far longer than I have patience to type. I had thought about RC cars, but they had always seemed (1) far too weak, and (2) not worth buying for just a handful of suspension parts. After years of searching, enter the Nitro, RC Monster Truck. They are heavily customizable/customized, so parts are easily available, heavy duty, and best of all, stock parts are always being swapped out for upgrades, so lightly used/new parts are dirt cheap. As mentioned, I've put together 3/4 of my suspension system for under $40 (just waiting fo the package to arrive), differentials will go for $10 a pop (was just checking out ebay for Revo Differentials this morning instead of working. Shhh! Don't tell my boss!), and all the U-Joints, shafts, and drive hubs (2 joints for each tire = 16 ujoints. Expensive to scratch build? Ugh yea!) for the entire vehicle can be had for $40: http://cgi.ebay.com/NEW-T-MAXX-3-3-E-REVO-DRIVE-SHAFTS-AXLES-DRIVESHAFTS_W0QQitemZ320453738368QQcmdZViewItemQQptZRadio_Control_Parts_Accessories?hash=item4a9c87ff80 > 3. My experience with 4wd shows, yes 8-inch wheels are better than 6- > inch, I used 8 inch solid lawnmower wheels on one vehicle and 10 inch > pneumatic lawnmower wheels on the second design. For my robot, I used > 6-inch RC buggy wheels, which cost an outrageous $40 a pair. Compare > that with the $10 gearmotors. > As mentioned, I've looked at lawn mower wheels, but the hard plastic... If you have any leads on ~8" pneumatic wheels with plastic hubs PLEASE let me know, as I haven't been able to find anything. I fully agree: $40 for a pair of shoes, and $120 for the whole beast is a very tough pill to swallow. > 4. Suspension is not really necessary, however, if you are using rock > crawler parts you are pretty much wedded to a suspension type design. > Honestly, it's not really necessary. I had been trying for ever to figure out how to transmit the power to 4 axles (I was thinking solid, no suspension back then), and kept going back and forth between gears and shafts, #25 chains, 2X4 wheel drive, etc. However, if one is going with a wheeled vehicle, the articulation granted by at least SOME sort of suspension system dramatically increases the contact the vehicle can have with the ground: vastly increasing mobility. Next up: if you're planning on playing with the big dogs, (tracked tanks) instead of simply running supplies, you're going to NEED that mobility given the inherent disadvantage of being an armored car. Plus it's a fun challenge, looks REALLY cool, and if you can pick up the parts isn't really all that much more than buying chains, cogs, gears, shafts, etc. :D > 5. Skid steering is a lot simpler, and works well in my 4wd vehicles, > although these vehicles are less elongated than a scale AC. The length- > to-width ratio affects the sideways load in skid steering. Skid > steering might work for a 8wd vehicle if you can pack enough torque > into the 8 wheels to overcome the sideways load, which will be high in > grass. Light weight helps in reducing this load. With agile skid > steering you can turn in place. > Agreed. However, then you get back to the problem of needed two, much higher torque motors, and the batteries to drive them: increasing weight and wear on the tires (assuming they're soft, grippy rubber). Then, you've got the issue of having to power 8 axles instead of only 4 (vs only 2 in a tracked vehicle), and that a major whoopla of problems to be sorted out with mounting bearings, shafts, chains/cogs/gears, etc. > 6. Direct drive (wheel attached directly to motor) is also a lot > simpler and cheaper than distributing power with shafts, > differentials, universal joints, etc. These parts together are a lot > more expensive than gearmotors, from what I can tell. > I couldn't agree with you more. But as each motor only has a maximum of two shafts (one at each end), you're either looking at (1) a 1~2X8 vehicle (only one or two powered wheels out of eight and that is just begging to get stuck on the first patch of wet grass), or the fun of trying to synchronize 2~4 motors. And as mentioned, I'd rather go for the simplicity of a single, moderately large motor. Thanks and keep the comments coming! :D > -- > You are currently subscribed to the "R/C Tank Combat" group. > To post a message, send email to [email protected] > To unsubscribe, send email to [email protected] > Visit the group at http://groups.google.com/group/rctankcombat _________________________________________________________________ Windows 7: I wanted simpler, now it's simpler. I'm a rock star. http://www.microsoft.com/Windows/windows-7/default.aspx?h=myidea?ocid=PID24727::T:WLMTAGL:ON:WL:en-US:WWL_WIN_myidea:112009 -- You are currently subscribed to the "R/C Tank Combat" group. To post a message, send email to [email protected] To unsubscribe, send email to [email protected] Visit the group at http://groups.google.com/group/rctankcombat
