B1M bolt-in mid motor conversion kit

[mk-Zero]

EDIT: I've decided to go with "B1M" as the official name for this car/kit. Yes, I had an earlier MM car that was a one-off that I called the B1M, but just think of that one as a very early prototype for this one


Some of you may remember my mid motor project from a year and a half ago: http://www.rc10talk.com/viewtopic.php?f=35&t=37008
The car came out great and drove really well. But what always bothered me about these RC10 mid motor conversion was having to hack up and drill the chassis, and that they don't look "right" with the rear shocks mounted to the back of the arms.

So last year when I saw the IFMAR winning B6 prototype with its laydown transmission it got me thinking: If I design an RC10 transmission case and lay it down properly, I can get the motor far enough forward in the car to clear the pan-- not cutting, no drilling!

Fast forward to now, when I actually have some time to start a new project. Here's the second prototype transmission, which basically proved to me it could be done

The transmission case is a 4-gear, which is necessary to move the motor far enough forward, but has the added benefit of providing more rear traction under acceleration. I plan to add shock tower mounting to the transmission case (either integrated or a separate bulkhead) to keep the shock tower in the stock location. This will keep the shocks on the fronts of the rear arms, like a proper RC10.

It looks like with my transverse shortie pack mounts there will be enough room in front of the battery for the ESC, radio, and servo, no problem.

The transmission case will use stock mounting holes, so no drilling will be necessary. For now I'm using the Stealth mounting holes, but I may actually change to the 6-gear holes and the stock bulkhead holes so it fits every chassis, again without drilling.

I have some ideas for bracing the rear of the chassis and the rear motor guard section of the chassis, more on that later.

In the end, I'll make all the parts available through Shapeways and myself so if anyone wants to build one they can. The nice thing is it will be completely reversible, so you can try it out and see how you like it without ruining a chassis.

[bjammin90]

Subscribed

[jwscab]

neat project. I'd use one set of 6 gear holes, and the bulkhead holes. make the bulkhead a separate piece that ties into top of trans and sides of pan. only sticky point is spur gear clearance on left side. shock tower would be a shorty, like an oval conversion.

[mk-Zero]

That's what I was thinking with the mounting: the rear 6-gear holes with the stock bulkhead holes.
For the tower, I want to maintain the look as much as I can of the stock one, but yes, it will be a little shorter since it's lower surface will be higher. The bulkhead will probably bolt to both the chassis and trans case. I may tie the chassis tabs into it, like the stock bulkhead. We'll see, there's more than one way to skin a cat.

[jwscab]

definitely strongly consider tying in the side tabs, as that gives you excellent rigidity, unless you come up with another strut or reinforcement system.

[mk-Zero]

That's my number one choice, but the challenge is the spur gear. It's going to have to go around it. I'll model something up, print one out, and go from there. That's the nice thing about having a 3D printer at home, I can iterate really fast.

[jwscab]

yeah, that's pretty cool. what model is it?

[mk-Zero]

Its a FlashForge Creator Pro.
It's become and indispensable tool for these types of projects. For instance, I did two transmission iterations over the course of about 5 days, and now I'm designing the 3rd. They print in about 2 hours. In the next few days I'm going to spend some time staring at the car, taking measurements, etc, and hopefully come up with a preliminary bulkhead design. If all goes well I'll print the first iteration of it in less than a week from now.
Jeff (GoMachV) will be producing the towers, but I can design, print, and test fit them before sending him the file, which will avoid wasting his time, waiting for shipping, etc.

[alien3t]

Whats wrong with the tower and bulkead, and shocks mounted to rear of arms? is it the stay old school look? I know yeah the new cars are that way.

only think i can think of is if you move the batter boxes out of the way, and lay the trans down more. the sput might clear the bulkhead area. than be easir ot wrap bulkhead over trans, witout batter cup area, and would possibly still use a stock tower? but woudl hav eto run a shelf for esc above motor, and put receiver on side by where spur is. or might have a little romm still up front?

[mk-Zero]

Yeah, it's mostly that I want to keep the look of the car as much as possible. Same reason that on the Ten4 we kept the front shocks on the front of the tower. You can fit a normal body, trim it as normal, etc. Besides, anyone can do things the easiest or most convenient way, but where's the fun in that? I like design challenges, it's what I do all day at work

I had already thought about putting the ESC on a shelf to save space, but quickly decided against it because I want to maintain a low center of gravity.

[heretic]

Nice! Love the idea. Since you're designing the transmission case "from scratch", what about offsetting the motor plate to the left to make the motor more centered? I guess that could cause issues with the top shaft (although a GT2 top shaft could help) and it could make it harder to locate the shocks to the front, though. Another question: with the motor so far forward, would it not put a huge stress on the 4 anchoring points on the chassis? Using the 6-gear holes (all 4 of them) + the front bulkhead holes does sound like a better option. Just thinking out loud... Anyway, looking forward to see what's next! Really cool!

[Niki]

Hey Brian. Looks fantastic. That is exactly what I had in mind to do also with the leading thought of not modifying tub chassis at all. I made a 3d test assy with 2 idlers like you and also 3-gear version with using 2nd diff gear as idler. This is great, now I can just lean back and see how your design builds up

[mk-Zero]

Haha, that's funny Niki, I guess great minds really do think alike

[durb69]

Def going to keep my eyes on this build! Wicked cool!

[atarit3]

very cool thinking. Will be watching this build, keep us posted!