OFNA Ultra MBX Conversion - The Latest Project

[MetalMan]

Reminds me a bit about when I drove my 1/8 buggy on the 1/10 track (it was worse for me because I had bad tires). I hope that 1/8 track opens up so you can get some real driving :004:.

looks good you just need more room to open it up

[crazyjr]

very nice buggy Batfish, looks like it fits my style, loosey goosey

[highhat]

Nice job! I'm currently in the middle of an MBX conversion myself. Any chance of some more pics of the finnished conversion? It looks like you moved the servos? what did you use to mount them?

Thanx
Robert

[Batfish]

Here's a new update.
First, one picture:


Now links to 9 more - I decided to save on the low-bandwidth folks by not posting 10 pics in the same reply :)
http://i20.photobucket.com/albums/b2...14-2006-01.jpg
http://i20.photobucket.com/albums/b2...14-2006-02.jpg
http://i20.photobucket.com/albums/b2...14-2006-03.jpg
http://i20.photobucket.com/albums/b2...14-2006-04.jpg
http://i20.photobucket.com/albums/b2...14-2006-05.jpg
http://i20.photobucket.com/albums/b2...14-2006-07.jpg
http://i20.photobucket.com/albums/b2...14-2006-08.jpg
http://i20.photobucket.com/albums/b2...14-2006-09.jpg
http://i20.photobucket.com/albums/b2...14-2006-10.jpg

So...I'll recap and describe it as you see it in these pictures.

We (CCristo and I) pretty much share responsibility for this project, and we're both pretty pleased with it so far :)

The chassis is custom cut from 3mm aluminum and extended 1 inch (to make mounting the batteries easier). This makes the chassis approximately .5 inches longer than most of today's 1/8th nitro buggies.
A UE 105mm dogbone was used from the center diff to the rear diff. The original OFNA front dogbone was used from the center diff to the front diff.
A rear brace was cut to go from the center diff to the rear diff. This is where the ESC is mounted.
A front brace was cut to go from the steering posts to the center diff. This holds the UBEC and the Nomadio Sensor transceiver.
The steering linkage was swapped from the right to the left side to accomodate the motor, which is mounted towards the front of the buggy rather than the rear (also to increase room to mount the batteries and help off-set weight).
I got a motor mount that Mike had originally prototyped for a HB center diff and we adapted it to the OFNA center diff, then mounted the motor forward with the pinion facing the rear of the buggy.
The steering servo is mounted laying-down on the chassis. It is a JR z8800t servo.
The brake servo (mechanical rear brakes) is standing up next to the center diff using Traxxas servo mounts. It is a BlueBird 621MG servo.
I swapped the c-hub suspension that was on the vehicle for the PBS suspension (personal preference).
We abandoned the E-Maxx battery trays in favor of GorillaMaxx straps and Associated battery cups. I cut the end cap from the cups and mounted them to the chassis to stop side-to-side movement of the batteries.
The motor is a Lehner 1940/6 hi-amp and the speed controller is the BK Warrior 9920. The batteries are FMA/Kokam BalancePro2S 2S2P 6400mah 20C packs, two of them in series. I use two of the BalancePro chargers to keep the batteries charged up during the breaks between practice/racing.

I'm hoping to remember my camcorder this Sunday for some video on the outdoor track. As it is now, the buggy easily keeps up with the nitros and can even outrun some of them. It definitely takes the prize when it comes to accelleration. :)

Feel free to ask any questions, as I'm sure I missed something of interest to someone.

[Romster]

Nice conversion and video!
What is the total weight on your buggy with batteries?

Nice work!!

I need details.
What are you running for gearing??
How hot does the 9920 get after 5, 8, 10 racing minutes ??

I have a hard time keeping the controller cool.

Looks good hope you do you good at the races.

[Batfish]

Weight: I still haven't actually weighed the buggy (the bathroom scale trick says about 9.5lb), but comparing it to nitro buggies at the track, I'd guess it's about a pound heavier, RTR. The biggest reason for the additional weight is the batteries and extended chassis. They are both necessary, however, to have the capacity to run the longer races with the nitro buggies.

Gearing: I use the nylon OFNA 51t spur. In the video I was using a 13t pinion. That gearing should get me about 28mph. I also have a 15 and 16t pinion. Currently, I have the 16t pinion in the buggy and will see how it performs on the track with the additional speed.

Temps: When I ran it on the outdoor track a couple weeks ago, it was 86F outside. After a 5 minute qualifier, the motor barely registered over 100F and the ESC was at 113F. The efficiency of the Lehner 1940 is what's keeping me safe. I'm pretty sure that I'd be heating up my 9920 if I ran an L or XL BK/Feigao motor for a 15-minute main. So far this setup has been proving itself worth the money. Believe me, I wish I could have gotten away with a $90 motor :003:
I also have the Associated fans on the ESC. As you can see, they fit pretty nicely and they plug right into a spare channel on the receiver. They are Associated part number 31036 and run about $20. It's more expensive than cheap fans you can find elsewhere, but they are a great size for the application and are pre-wired with the servo-type connector.