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To tide this thing over until my final exams are done, here’s the latest render straight out of the manual:
Special features include infinitely-adjustable suspension stiffness (yes, infinite :)), quick-release battery strap, Delrin everything in the rear pod, and a new motor mount that doesn’t need drilled cans.
I haven’t come up with a good enough servo saver so you’ll need a servo saver intended for 1/18.
With a Ti-shaft ball diff and the small electronics (the new ASF board is just one possibility) the MRCG should weigh around 135g without body; that’s 5-10g less than a similarly equipped MR02, not too bad.
Funding isn’t a huge issue, but I’ll let you know ASAP when I can put a delivery date on these chassis.
I took the RM car to the tennis court recently, drove over 2″x1″ ruts (2″ wide, 1″ deep!) in the concrete, heard the chassis smack the ground each time, but nothing broke or loosened up. That’s good from a durability standpoint. 🙂
Even with the batteries pushed full forward, the car has massive rear grip. I was still using medium-compound GRP foams front and rear so it should’ve spun like a top, but all I got was a moderate degree of understeer and a little slide if you brake too hard and wrench the wheel. I’m more than happy with the results.
Cleaning is about the same time-wise as your average MR02. For those concerned about electronics: I didn’t have any glitching issues despite all the dust on that board, but you may want to seal/heatshrink/case electronics if you drive in more rigorous environments. Indoor cars will have no issues.
I’ve also been working on the MM production car, of course, and the G10 chassis parts are already done:
And I’m just working on the production motor mounts (Delrin rear axle bearing carriers are done, just need to change some settings to make it easier to slip the bearings in). My apologies for the picture quality, but it’s tough to lean into the enclosure while trying to hold a steady hand, lol…
Anyways, we’re pretty close to release and you can rest assured that the pictures and news will be everywhere when that happens. 🙂
The horn pokes up from behind the tierod, and two flat G10 pieces are to be screwed on perpendicularly to the tierod to form a slot around whatever’s poking out of the servo horn.
It’ll make sense when I finish the build. 🙂
Edit: and it is, with the exception of a battery pack and a bearing set, complete! The tierod “horn” consists of two glued-on G10 pieces right now but as mentioned above will be screwed on in the final car.
Edit: Considering the ball diff, motor mount and oil damper, it appears I’ve managed to shave a few grams off the MR02’s chassis weight:
Got some more work done. The car is currently riding on plastic and metal bushings (!) so don’t expect it to run quite yet.
Note the new uber-low oil damper config. Now the only things that even reach wheel level are an antenna, two motor wires and a crystal holder. That’s pretty darn low if you ask me. 😉
Front end detail: Kingpins are held up by exactly 1/8″ of fiberglass milled to spec, it’s stiff. I also got a clean conversion on the HS-50; you’d have to know beforehand that it was a 3-wire servo… 🙂
Rear end detail: Got those side springs in, they work well and don’t click on the spring perches as I had worried about earlier. Also illustrates the height of the oil damper and the amount of leeway you have to shift the batteries back and forth.
First functional prototype!
Pics first.
Comments:
1) The mill countersunk two of the holes a little deeper than the rest. This might have something to do with my fixturing platform (it’s not perfectly trued yet), so I’ll look into it.
2) I accidentally used climb milling for everything, and had to file the parts a bit to get the finish you see here. Still, not bad.
3) The chassis went together very smoothly. After the finishing filing, I had only minimal filing to do to make the kingpins fit into the holders. And once in, they are very snug.
4) The rear suspension is a good stiffness up and down, but the roll stiffness is rather high, even for my tastes. I do not know how this will factor into real-world driving yet.
5) The front end will not flex unless you hit something really hard. I’ve been testing it with Kyosho hard springs and so far there is no visible flex.
6) The tierod movement is a little bit stiffer than the MR02, although this is partially because I preloaded the hard springs.All in all a decent job, I hope to have the elecs soldered together quite soon and some bearings, wheels and tires (doh, I sold ’em…) and this car will be ready to go!
Ok, I’ve got good and bad news.
Good news first: edge quality is perfect on the longer cuts.
Bad news: edge quality on the countersinks has gone down.
Worse news: the mill seems to jam up right around this one spot of travel. I have no idea where to look for the cure; the mill is freshly lubed up with WD-40 and the rails are clean. Yet there’s a slight grinding noise and sometimes the whole thing just jams while the CNC control software believes it’s still going.Check Exhibit A:
I was using the wrong units! D’oh. I have the feed rates right this time, and edge quality is much better, though the cutting bit didn’t go deep enough to separate the pieces entirely from the stock. (It turns out that this plate of fiberglass is slightly thicker than 1/32″.)
If you look closely at the picture, you’ll notice there are two “kinds” of edges. I was playing around with the settings and found that really slow speeds (6mm/min) are really good but take forever, slightly higher speeds (15-30mm/min) are terrible, and the proper speed (150mm/min) nets nearly perfect cuts (check the outside edges of the flex plates).
So that’s my update. Since I have a 3-day weekend I should be able to do some more work on the fiberglass and get that all sorted out and perfect. The Delrin and aluminum parts may have to wait since I still need some screws to mount my micro vise to the rotary table. Rest assured I will get this done as fast as I possibly can!
First batch of G10 prototype parts! The cut quality is no good, but it’s mainly because I used a ruined endmill to cut with. The holes will be countersunk later, no worries.
I plan to get these parts made correctly before moving on to the fancy 4-axis work, so check back for updates. 🙂
