The Craftmans Shop > Radio Control Models
Bruder Manitou 2150 - RC conversion
ddmckee54:
OK, I need to hear some opinions - from someone other than the voices in my head.
I has originally planned to fill the hollow portion of the original Bruder wheels with a BB/silicon seal mixture that would have been basically troweled into the hollow wheel. The Bruder wheels have about half of the sidewall cut away on the back of the wheel. The BB mixture would have been troweled into what's left on the inside.
Me and the voices are starting to think that's a bad idea for a couple of reasons:
1 - It would probably stiffen up the tire sidewalls too much. You want to have some give in the tire sidewall because every tire has some degree of "squat" to it. A BB/silicon mixture wouldn't flex that much.
2 - Troweling that mixture onto the inside of an existing wheel opening would be messy at best.
3 - I did some off the cuff calculations and depending on how well the BB's packed together, an estimated 50-75% fill, the common copper coated steel BB would add between 1-1.5 pounds per wheel. I'm using the same gearmotor that RCMODDER used in his CAT Telehandler conversion. They might NOT handle the extra load, 4-6 extra pounds could be overkill.
Plan B is to redesign my 3D printed rim. I think I can remove a good chunk of that part and still keep a 2-3mm wall thickness everywhere. I'm estimating that a cylinder with a 60mm OD, a 50MM ID, and a height of 15mm could be removed. This should give me a usable volume for the BB mixture of about 130cc or roughly 8 cubic inches - IF I did my arithmetic right. Using my 50-75% fill guestimate, I should get an additional weight of an estimated 0.5-0.75 pounds per wheel. Plus, since the inner rim still has to fit in the available sidewall opening, I could 3D print mold parts to ensure the inner rim would fit in the wheel opening.
Do I hear any Plan C's?
Don
russ57:
Think I need pictures of the wheels.
But what about a polyurethane foam as filler?
-Russ
WeldingRod:
I would load test the wheels to see what you think of the loaded shape!
You could glue short bars into the tires with space between them to get weight with less change in stiffness.
If you can find/make small foam pellets you could make your bb/silicone more flexible. A close packed bb/rubber thing will be very stiff. Adding compressible stuff to the mix will help that. A monolayer of BBs glued in would be less stiff but still rim weighted.
A loose steel doughnut in the tire with clearance equal to the squish you want might be an improvement. It would allow squish but still keep the tire on the ground AND be dense. Do you have a lathe? Cast lead or solder doughnuts are another possibility...
You might mould one to roughly the right shape and test its flexibility!
Hub weight makes sense!
RC truck folks use foam doughnuts in the tires to adjust stiffness.
Sent from my SM-G892A using Tapatalk
ddmckee54:
I've been working on the design for the attached garage that I want to have built this summer, so I haven't got a lot done on this project lately.
What work I have done, has made me revise my original estimate of the inner rim volume available where I can add weight downward - a lot. Instead of a tube with an OD of 60mm, that's 15mm tall, with a 10mm wall thickness - the wall is only 5mm thick. I may actually need to find another spot to add weight to the tires.
The room inside the model is kinda' limited and I don't want to waste any of it on dead weight. I might be able to add some weight in the upper body, but I'm building this thing from the ground up so I want to keep all the interior volume open in case I need to jam something in there. You know, the unnecessary stuff like batteries, receivers, servos, light controllers... that kind of stuff.
I'll try to remember to get a couple of cross sections from my 3D model of the wheel. Pictures don't turn out that well. Since I'm printing most of the wheel parts in black filament, there's not a lot of color contrast between the Bruder wheel/tire and the parts I've printed. Which I guess is really a good thing. The last time I worked on this project I had found a spot where I might be able to add additional weight without affecting the sidewall stiffness.
Don
ddmckee54:
A disappointing update.
A couple of weeks ago I went into Cabela's to look at some shotgun shell reloading supplies, I wanted to check into getting some lead shot to use for wheel weight instead of BB's. Cabela's is a large chain of stores supplying hunting/fishing goods - for those not on this side of the pond.
I was talking to the nice man at the counter and we got to looking at what size shot was available, and what they had in stock. I wanted something smaller than an ordinary BB. A BB has a 0.177 caliber so there would be a lot of air between the BB's. That's what got me to thinking about shotgun shell reloading supplies. The smallest shot that Cabela's had in stock was 25 pound bags of #6 shot, way too much in both quantity and physical size. 25 pounds would probably be a 2 or 3 lifetime supply for what I want to do, and #6 shot wasn't THAT much smaller than a BB. Plus I didn't want to spend $50 just to find out it wouldn't work. We determined that #12 shot would be just the ticket, if I could find it because Cabela's didn't stock it - anywhere. #12 shot is a maximum of 1.3mm in diameter and is used for "snake loads". The round will blow the hell out of a snake at a few meters, but not do much damage to anything over 10 meters away. I went on-line to the only reloading supplier that had #12 shot and ordered an 11 pound bag. Surprise-surprise, with shipping it STILL cost me about $50.
Anyway, I printed up some containers that fit in some of the unused volume within the wheel. Even with the small volume that I initially printed I'm getting an additional 85-90g per wheel, and I can make the containers a lot bigger.
Last weekend I got the brilliant idea to bury the motor leads within the axles that I printed. So I spent Friday night and Saturday morning redesigning the axles to hide the motor leads, I had some other improvements that I wanted to make to the axles anyway. I even redesigned the gearmotor housing to cover and route the motor leads - it was BRILLIANT! Then that little voice in the back of my head made itself and its' question heard. "Does this clear the frame of the crane?" AWWWW CRAPPP!!!! IT DON"T FIT!! The motor leads are entering the axle within the frame where's there's absolutely NO clearance. Not only that , but the gearmotors JUST clear the frame. That's just the gearmotors, NOT the gearmotors AND their wires. Not enough clearance, maybe a mm. And the ribbon cable is 1mm x 2mm, 1-2mm more clearance and I'd be happy.
My Brilliant Idea turned out to be a Brain Fart. I wound up throwing away 90% of 2 days work. Plus I now know that I've got to redesign the back of the gearmotors, and this time ALLOW for the wires coming off the back of the motor when I check clearances. (Remember to CHECK the clearance to the frame too ya dummy!) I really am getting closer to putting this thing back on its' wheels - at least that's what I keep telling myself.
It's always the simple things that bite you in the butt.
Don
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