Perreault985

Hi there, I'm new to the forum and am posting a few pictures of a 1/3 scale buggy project I've started. I have been in RC for about 25 years, but have never attempted a scratch build before. I have sketched up the design over the past few months and started the fabrication a couple of weeks ago. The frame is tacked together and I'll be starting the suspension soon with some luck.


There are a couple of pictures attached. The first is the sketch and the second is one of the frame as it is today. Any general suggestions would be appreciated and I'll try to provide an update once a few more things come in to line.

Dirty_Vinylpusher

Tidy frame.
I like!

Lars from Norway

A man with what seems like a good plan! I like the frame too, looks very much to end up like a cool looking buggy. Please do keep us updated here.

fibergless

Wow! I like this project!

Perreault985

Thanks for taking a look, I am going to ask to see if anyone has tried using two one way bearings for a rear differential. As the car rolls around the corner the outer wheel will begin turning faster and begin to freewheel allowing the car to corner. If the inside tire begins to spin, the bearing will re-engage and act sort of like positraction. Does this make sense?

Boca bearings: http://www.bocabearings.com/productD...x?ItemID=14517

The torque of a 4-5hp pocket bike engine geared at 4:1 is about 13ft.lbs (17Nm) by my estimates. These one way bearings should hold up, I think. I'm using a 5/8" shaft with the one way bearing pressed into a piece of DOM structural tubing (0.085 wall) with a 1in O.D. There will be shaft seals on the ends to keep out the dirt and keep the grease in. I'll then fit it with a sprocket over the tubing and drive it with a chain. Any input would be appreciated.

Dirty_Vinylpusher

Interesting....

It does sort of make sense I suppose but I'm not sure how well it would actually work.
I think there will be a lot of skidding and counter skidding once the bearing kicks back in....

You probably can't quite compare it to positrac like that on bobcat machines etc as they have individual drive/power delivery to both sides.
But I would be interested in seeing how/if it works!

Mudgy

not a bad idea, older 1/10 nitro 4WD's had an option one way front diff... My machines use these bearings/sprag clutches a lot, and you'll find grease may be too heavy for the shaft rotation speeds. Maybe use oil, start off with a thin one, and get heavier as you go to find the right weight. In some of our hand tools, even motor oil is too thick for the one-ways. INA make them too.

Perreault985

Thanks for the thoughts about the one-way bearings. I hadn't even considered the weight of the oil or grease, I'll be sure to start off with something lighter.

I've made a little progress, but football play-off games take precedence here in the US. I did make up a jig for the suspension arms and have them all tacked together. I also finished the back hub and stood it up next to the car's frame. I've attached a few pictures of what I have gotten done, so far so good.

Lars from Norway

I like what i see!

Perreault985

It's coming along slowly, but the rear suspension is finished. I didn't get to mount the shocks horizontally in the rear as I'd intended and went with a more conventional configuration. I'll really try to work through it and make the horizontal monoshock in the front work.

Lars from Norway

That looks nice! Are you going to make the front monoshock something similar to what i did here on my car?: http://www.rcuniverse.com/forum/rc-g...l#post11537473

Perreault985

Yes, that's the idea. When we were kids, my best friend had a Tamiya Fox and I thought the mono shock was so cool. I'll also need to rig up a stabilizer bar to keep both wheels planted. Still looking at yours and wondering where you came up with that setup? It is so unconventional looking, I like it...

Lars from Norway

I guess i stole the idea from the old Tamiyas as you are saying here, but the stabilizer is stolen from already existing onroad-cars. I soon realized that i had to make one, when one of the sides got compressed the other side would lift itself due to transfering the motion over to the opposite side via the shock, so something had to be done I was going to make a traditional one with a "U"-shaped bar with links attached to the A-arms (more like on the rear of the car), but i ran into some space issues so i thought it would be cool to try this one

Perreault985

So, I've spent the last few weeks working on the radio system. I've never tried a FlySky radio before, but so far so good. The system has everything I'll need and was a great price at $65 USD. The receivers are $8 each and a good thing since I fried one in the process of wiring things up. I picked up a giant scale servo and motor controller at Pololu and was able to put together the steering servo using a wiper motor. The Pololu controller worked like a charm and I've attached a few pictures showing each component of the system.

Britishman00

It looks really good so far buddy. Will be good to see it when its finished, whats the next step?

Perreault985

Thanks, I'm working on the front end now and hope to finish it up next weekend so that I can post a few pictures. Suprisingly the monoshock is working out for me in the front as I'd planned. Once the front suspension is mounted I'll start working on the steering linkage and bellcrank assembly.

After that I'm moving on to the driveline and fabricate the halfshafts with the one-way bearing differential system I'd mentioned earlier.

Lars from Norway

Hope there are many pics to come from the work ahead! The one-way bearing-diff sounds interesting!

Perreault985

I've got the front suspension done and mounted it on the frame. It's starting to look like a buggy now that there are four wheels installed and the mono-shock works pretty well. I've attached a few pictures showing the progress.

Lars from Norway

Looks very nice! A proper buggy! But i wonder why you haven't put the shock between the lower A-arms? I see some issues with lack of space as it stands now, but there is always a fix to a problem

Perreault985

Thanks, it is coming along as well as I could have hoped. As you pointed out there were space issues putting the shock down between the uprights. I'd worked on several different configurations during the design phase and actually liked the idea of the shock exposed on top. From a functional standpoint I didn't think there would be much difference between mounting it low or high.

The most challenging part of the design for me was finding appropriate 1/3 scale parts and keeping to my $1,000 USD budget. The "shocks" I ended up choosing were inexpensive bicycle shocks and limited some creativity as they came with 350lb springs. I had to come up with a design where 25lbs of force on the end of the arm would compress the 350lb spring.

Perreault985

So there was a good excuse to take a video this weekend as I was able to test the steering and rolling chassis. I had my lovely wife give the buggy a push down the driveway and was able to see how things looked moving for the first time. So excited to see something move after working on this all winter. The video link is attached.

http://youtu.be/p2s9h-6gInc

C.lyra

Looks nice.. Canīt wait to see more of this baby in action....

Perreault985

The one way bearing differential is finished and mounted on the car, everything fit together and spins true. The next step will be to mount an idler shaft and pulley and wrap up the driveline. It's getting warmer out and other projects are beginning to take priority. I had hoped to make a powered test drive before the summer gets here. Attached are a few pictures of the differential and driveshaft.

Apachy

Mate, I'm intrigued, tell me more about the one way bearing differential - I used such bearings on the old HPI Savage starters but struggle a tad to see how that will work (only reverse really correct. Anyway - TOP JOB MAN

Can you provide some more details on the assembly and your manufacturing process. I think it's genuis BTW

Great stuff - Apachy

Perreault985

The one way bearings were the means to an end as I was looking for something inexpensive that would fit the scale of the buggy. I'm not 100% sure how they are going to hold up nor how well they will work under full power. I can tell you they do work perfectly when the buggy is rolling around on the floor.

As you can see in the pictures above, the drive shaft is split in the middle and two one way bearings are housed in steel pipe with a sprocket mounted on it. The idea is that both wheels will be engaged as the vehicle is driving in a straight line and both one way bearings are locked under power. Once the buggy begins a turn, the outer wheel will begin turning faster and disengage the one way bearing allowing it to "free-wheel" around the corner. The inner bearing should stay locked under power and continue driving through the corner. If the inner wheel looses traction and begins spinning faster, the outer bearing should lock up again and begin putting power down again. I'm hoping it will be sort of a poor man's posi-traction. I've attached a drawing below for the sake of clarity.




I'll try to add some more detail about the build and include a my calculations and estimates for the for the scale size, weight, shock rate, drive ratios, etc. I'll also post a bill of materials showing how I kept to my $1,000 USD budget. I could also share my model in Sketchup and provide a link to it there.