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Looking for Some Advice on a Home build ....

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Looking for Some Advice on a Home build ....

Old 12-04-2015, 01:32 PM
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ThatDamnGuy
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Default Looking for Some Advice on a Home build ....

Well hello to everyone on here, I would like to start by saying this forum is awesome and I have got lots of information off here over the years. I am looking to start planning a project and wanted to turn to the forum for some advice. Any advice, tips, or personal experience would help. I have a small machine shop so I will be machining a lot of the parts. Here are a few of my questions, please feel free to add anything to the list.

Project Idea:
Gas 4x4 Stadium Truck, not sure what scale or if I am even worried about a scale.

Questions:
#1 what engine (I know this will have a lot to do with the size of my truck but Im open to any feedback)
#2 Belt, chain, or shaft drive
#3 Chassis material, aluminum or steel

thanks to anyone that can provide some insight ....
Old 12-07-2015, 08:47 AM
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Maj_Overdrive
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For a first build I'd go large scale 1/4, 1/5, easier to work on and make parts for as in general the parts don't need to be as intricate. This size also lends itself to 23-35cc weedwacker and chainsaw engines as well as more rc specific engines of the same size.

The type of drive depends a lot on your abilities and how much you want to make yourself. Making the ring and pinion gears for a diff that's shaft driven can't be the easiest thing to do. But shaft drive may be easier to do 4wd especially if you're willing to rob some diff parts from a production rc. Chain is usually a bit easier than belt as you can adjust chain length yourself instead of finding a belt the right size and belts usually need a tensioner where chain may not.
Old 12-07-2015, 10:13 AM
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ThatDamnGuy
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Maj_Overdrive,
Thanks for the feedback. I was leaning towards a 1/5th scale and I have a few weed wacker motors to play with. I like the idea of doing a shaft drive for the 4wd and I think it will be fun to machine the parts anyway. Making diffs and stuff will be all new and as far as gear ratios I have a lot to learn. I would also like to see about making a 2 or 3 speed transmission. anything I should watch out for whit motor selection?
Old 12-09-2015, 08:29 AM
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I'd do a tube chassis using 4130 chromemoly tube, you can use a mix of 1/4, 5/16 and 3/8 with .049 wall thickness...stuff is light and super strong. definitely shaft drive.
I always used OBR full mod motors, super reliable and make plenty of power. if you do 1/5th scale then 30-35cc is more than enough, if you bump up to 1/4 then maybe consider a twin I put one in the 1/4 FOFF jeep I built and it was more than enough to propel 60lb or so up near vertical hills.
My next build was going to be a 1/5 scale tube chassis short course truck with a live rear axle but unfortunately I'll probably never get around to doing it now...too busy with other projects and sold all my rc stuff except for my 5ive.
Old 12-11-2015, 01:50 PM
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Thanks moonman007uk,

I think I am going to go 1/5th scale and a tube style chassis, but with front and rear bulkheads. Kind of a hybrid between a tube design and a pan style chassis, that way I can make changes in the suspension without rebuilding everything.
Old 12-11-2015, 06:12 PM
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There's a couple things to watch out for when using weedwacker and other power equipment engines. Some have the pull start on the same side as the output shaft, particularly weedwackers. I had an old Ryobi like this and the real issue was the clutchbell needed to be supported on the side furthest from the engine. It wouldn't be a big deal to make a plate with a bearing but that plate would be attaching to the plastic pull start housing and who knows how long it would last. Another issue with that engine is the intake port is located on the crankcase instead of the cylinder sleeve and doesn't develop as much power. At least it was a freebie but it put my plans for finally doing a home built rc on hold.
Old 12-14-2015, 08:34 AM
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Maj, thanks again! I have 2 or 3 weedwacker motors sitting around so thats prob what I will go with for now, then upgrade later. any suggestions on a transmission? Is there a 2 or 3 speed out there that you would recommend or is it even worth it? I have the tools to build one but I would need to do a lot of reading on how they work and gear ratios first. What are your thoughts?
Old 12-15-2015, 04:58 PM
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All Automatically Shifting multi speed RC transmissions are basically the same and use centrifugal force to do the shifting. Most are a pawl type, where a little metal arm (the pawl) is spring loaded and extends when there's enough centrifugal force to engage the drum directly over it that is the next gear. How the pawl engages the drum varies, could be notches in the drum or pins the pawl engages, either way it does so with a bang. A few use a clutch (LST) instead of the pawl for smoother engagement but it's still centrifugal force acting on the pawl or clutch and the springs keeping it from being engaged too soon.

The simplest example I can give is 1/8 onroad cars and other external 2spds. On those cars the clutchbell has 2 (sometimes 3) gears on it, one bigger than the other. Those gears are in constant mesh with the corresponding spur gears. 1st gear is obviously a small pinion with large spur. Now the 1st gear spur rides on the input shaft using a one way bearing. Spin the spur in the proper direction and it turns the input shaft which obviously the engine should do. The 2nd gear spur uses regular bearings, spin it in either direction and it has no effect on the input shaft. The pawl or clutch inside the 2nd gear spur is attached directly to the input shaft though. Once the 1st gear spur gets the input shaft spinning fast enough the pawl or clutch engages the 2nd gear spur. Once the 2nd gear spur is engaged it's going to try and spin the input shaft faster than the 1st gear spur was spinning it. This is where the one way bearing on the 1st gear spur comes into play as it allows the input shaft to spin faster than the 1st gear spur.

Want to make a 3spd? Then put the 2nd gear pawl/clutch on a one way bearing and attach the 3rd gear pawl/clutch directly to the input shaft.

There are 2spd kits available for the HPI Baja and I believe some other 1/5 vehicles. There would be a good place to start researching gear ratios and possibly adapting already built parts to your application.

If you're talking about a transmission you shift from the transmitter then I got nothing for you. The only TX shifted trans I know of offhand is the Emaxx and the Tamiya 3 speeds used in their tractor trailers and the Hilux and I'm unsure of their exact inner workings.

Last edited by Maj_Overdrive; 12-15-2015 at 05:08 PM.
Old 12-18-2015, 01:29 PM
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Once again Maj, thanks for the info!

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