Jammin X1-CR HV conversion

Hi,

I've had some interest from another thread to know more about my hopeful HV conversion of a Jammin X1-CR buggy. I decided to create my own thread about it...

Well, a few months ago I was inspired to get back into RC cars after a 15 year break from them when I last had an RC10 Team Car (which I'm getting running again too). After looking around at what's available these days I was totally amped to get a 1:8 buggy, but at the same time really bummed when I realised not a single manufacturer electrifies their 1:8 models by design. I have never touched an IC engine and intend to proudly continue avoiding them.

Ok, so after looking around a lot I decided to get a Jammin X1-CR Factory Team Edition. I have spent the past few weeks reading, learning, and planning how I am going to go about converting it. I have been flying electric helis for the past 2 years, and in heli land HV is very much the way to go if you want an efficient, high performance heli. So it is my intention to go HV in my car too with the hope of achieving high efficiency and light weight.

After building the rolling chassis I have looked at this from alot of angles. I have considered weight distribution, efficient and neat use of available chassis space, minimum running weight, optimal gear efficiency, gear tunability for track or straight line, and optimal motor RPM.

This is the power setup I am currently shooting for:

Motor: Neu 1912/1Y (825 Kv, 8 pole inrunner, 2500 Kw max)
ESC: Kontronik Jazz 55-10-32
Spur: Custom made 56T Mod1 w/ 10mm face width in Acetal Resin (Delrin)
Pinion: 16-24T (stainless steel, 7mm face width)
Motor/Diff Mount: Custom made, see below
Battery: 2x Maxamps 5S 2100 20C packs connected in series

Why Neu 1912? It is over 90% efficient. It has gobloads of torque being an 8 poler. It has an excellent rep in heli land. Its Kv puts it at 30500 RPM on 10S which makes a wide range of gearing very easy in a car. That RPM also puts the motor at the very peak RPM when iron losses become too great. In heli tests of various motors it has been shown many times over that to get peak performance from a motor a good starting point is to run it just below the point where iron losses cause heat to escalate exponentially. The only downside of this motor are the big gaping holes that will need to be sealed.

Why Jazz 55-10-32? It is the only ESC that has a "car mode", is 10S capable, and can control motors of more than 2 poles (it's been run all the way up to 14 pole outrunners).

I need to up the spur to 56T because the Neu 1912 has a 1.96" case diameter. Although smaller gearing will produce adequate gear ratios, the motor case will touch the drive shafts with all but very tall gearing. My choice of large pinions has a desirable side effect: most gearing is cut with a pressure angle of 20 degrees (including the ones I'll use). At that pressure angle the minimum pinion you can (or should) run is 18T so as to avoid undercutting, wear, and noise.

This is all a very BIG experiment for me. The components I am aiming to use aren't very common in car use at all so I really do not know how this will all perform. I have no reason to suspect it won't work, but I have no experience with converting (or even running) a car on brushless power. :) I only have others' experiences (both car and heli) to lean on and adapt.

Only the Jammin kit has been purchased so far. Right now I am in the process of getting quotes for my motor/diff mount design to be machined, and am also in the process of sourcing the custom spur gear. I will also need to modify the stock steel spur gear to turn it into an adapter plate to which I can mount the custom spur. I hope to get these parts completed within the next week or two.

From there I will order the power system. That will take atleast 3 weeks because it all has to be shipped from the USA.

Well, I've attached a couple of diagrams for you to see. I've tried to design the motor mount in the hope of it being sufficiently strong and light weight at the same time (approx 60g). It is to be milled from a plate of 6061 60x70x9mm. The diff holder is a mirror of the motor mount without the motor section.

Later on I will post my planned component layout on the chassis.

I'm keen to hear your comments and suggestions!!

[pb4ugo]

All sounds cool, with only one hesitation in my mind.

How many spurs you gonna have made and at what expense? Could you use much more widely available Ofna 51t spurs (and diff) With LSP r&p and large motor pinions? That should give you enough clearance as well as plentiful (and cheap) spur gear availability.

[jnev]

It should be an awesome conversion. Good luck with it.

[BrianG]

Sounds like a nice project! Good luck and keep us posted.

[jhautz]

Very interesting conversion you have planned. Its WAY outside the box!!

Just some quick questions that come to mind.

It sounds very heavy with 10s and that big motor. Is that heavy of a power system really necessary for a buggy? Most find they have more power than they need or can use with the Neu 15** series motors. It sounds more like a heavy Monster Truck setup.

I am very curious to hear about your experience with the the Kontronik Jazz 55-10-32 ESC. I dont know much about it but it sounds like it has some very impressive capabilities.

I gree w/ CoolHand... Could you use the 51T Ofna Spur? They make them in Delrin and if you want more strength could you just mount 2 of them against each other to double the surface area.

Killer project tough... I cant wait to see the progress!!!

On the spurs, they will cost about $30. It becomes exhorbitant if they wear out or continuously strip, but assuming they have a long life it's not a big deal to cough up the extra cost. Given 7mm face contact width, acetal resin material, and hopefully no undercutting from the pinion, I am banking on them lasting a long time. If they don't I will need to rethink my design!! :)

I have considered the 51T Ofna spur. There are a couple troubles with it. First there are no published measurements of it regarding the spacing and size of its mounting holes and they're not a stock item in car hobby shops here for me to go look at. I plan to use the stock 48T spur as an adapter plate which leaves only a few mm of tolerance for drilling extra mounting holes without sacrificing strength - the 51T might be too small and too thin around its outside for mounting like this, and its small size would probably require me to machine away the teeth of the stock spur so that they don't get in the way - with a 56T spur I can leave them behind and just drill 4 mounting holes. At 51T my low speed gearing options will be limited until the motor case touches the drive shafts. It will also mean using smaller pinions which exceed a pressure angle of 20 degrees.

With my intended pinion range of 16-24T I can gear for 30MPH to 50MPH. With a 16T there will be about 3-4mm of clearance between the motor case and the drive shaft, which leaves me with some breath room to add a cap to the front of the motor to seal its big holes.

The 1912 is the same power rating as the 1512 but is 2 oz. heavier. I have considered the 1910 to save weight, but it would have a big drop in max power and from what I've read 2000+W seems to be what you need in a 1:8 buggy?

The packs will add 500g of weight. I got the impression that 4S 8000 MAh was common in buggies, and those weigh 725g...

The really nice thing with the maxamps 2100 cells is that they are only 100mm in length. That will let them mount very nicely in my chassis without them pushing up onto the dust guards. I will post a diagram of my planned component layout a bit later...

Thanks for your input!

Made a quick diagram of the component layout. You will need to use your imagination because the photo I took was not from directly above, so the battery packs look like they'll clash with car components. They should fit perfectly, however. :)

[vad]

Aragon,
If you need some demensions on the 51T spur gear let me know. What you should see in the pics below, is a Hyper 7 center diff, with a 51T Ultra MBX spur gear. The adaptor you see there is from JT Racing. The adaptor was originally ment for the 62T dominator Steel gear, but the 51T delrin spur from the ultra series buggies fits just fine. Someone should suggest to Mike to order 20 to 30 pieces, bet they will sell on his website.

[coolhandcountry]

I am interested in how that neu does. Keep us updated.

[vad]

Aragon,
forgot to mention the hyper 7 diff fits in the MP-7 series buggies, Hyper series buggies, jammin series buggies and Hot Bodies series buggies. Not for mugen.

That is very nice. What you've done is essentially what I plan to do with the stock spur to convert it into an adapter plate for a custom 56T spur. The 56T is big enough to clear the teeth of the 48T so all I'll do is drill 4 mounting holes in the outer edge. It will look a bit like a 2 speed gear when done.

Your photos are very clear, thank you. Could you measure the diameter of the Hyper 7 diff casing please? I will keep this route in mind.

[remie]

@vad

Can you post or PM me the dimensions of the 51t spur?

[vad]

Originally Posted by Aragon

Your photos are very clear, thank you. Could you measure the diameter of the Hyper 7 diff casing please? I will keep this route in mind.

The diameter is 30mm.

Hi

My project is progressing slowly. Got my motor mount from the machinist today. Couple of issues to sort out, but it's coming together atleast.

I've posted some photos here.

[Serum]

Mike makes those adapters himself. have you got a partnumber of the HR adapter?