Jump to content
speedy_w_beans

Mad Bull Refresh

Recommended Posts

I built a Mad Bull about a year and a half ago for the beach, and like my Grasshopper it's time for a refresh before we go to the beach again this year (Grasshopper refresh thread http://www.tamiyaclub.com/forum/index.php?showtopic=73194).

During the initial build I made a few small changes:

- The motor pinion was replaced with a steel pinion

- All bushings were replaced with ball bearings in the gearbox and wheels

- The "shocks" were swapped for real oil dampers

- The link between the steering servo and bellcrank was replaced with a turnbuckle and ball cups

The first beach run was ok, but it was clear the silver can and TEU-104BK needed to be replaced with a brushless system. I had a spare Castle Sidewinder SV2 ESC and bought a Turnigy Trackstar 3250kV 4-pole motor, and that really breathed some life into the chassis. The second beach run was much better -- all that power and the large tires made it a blast to drive in the sand.

I still had a few NiMHs and was using them last summer, but over the past year I've given away almost all of them and have focused exclusively on LiPos. Since hard case LiPos don't fit in the stick pack slot on the Mad Bull, I wanted to do something to make this model usable once again.

The following pics show what I've done...

IMG_1435.JPG

It's not obvious from the picture, but all of the tires now have a few short strips of duct tape inside them to balance them better. Three strips of 3" long duct tape are placed on top of each other inside the lighter section of each tire. Almost all of the vibration caused by tire imbalance is now gone, this provides a little better control and it definitely looks a lot better when driving fast.

The center section of the tub chassis and the steering servo have seen some changes. The top plates normally installed on top of the tub are gone, and one of the servo mounting plates has been trimmed back so the tub is completely accessible. To keep the servo from rocking back and forth, high density foam is sandwiched between the servo and some interior walls molded into the tub. The servo is rock solid with the foam installed.

In the center of the tub there were several tabs molded in place; these were all removed so there would be no interference with a shorty LiPo. More high density foam was used to make a pocket for the battery. Excess ESC and servo control wires are hidden under the foam. The LiPo is held in place with a HPI 25mm x 270mm Velcro battery strap; slots were cut in the tub between reinforcing ridges. With this arrangement the battery is firmly held in place and protected by the foam, yet it's easy to change with the body removed.

The battery takes up most of the tub, so I needed to find new locations for the ESC and receiver. The slope of the body is such that the ESC can fit right behind the rear body post. I made a small ESC tray from an old plastic box; the box lid was marked and cut to provide the mounting surface, and it's captured by the two screws that already hold the body post and antenna tube in place. The motor wires route under the ESC through the original battery slot, and are zip tied in place to keep things tidy. The ESC power wires are also zip tied to keep them in place, and the Dean's connector I originally used has now been replaced with 4mm bullet connectors.

IMG_1438.JPG

The radio receiver is actually mounted to a plastic tub wall immediately behind the LiPo. The reasoning here is that most sand and splash should be flowing from front to rear, so hopefully the space right behind the battery provides enough of an obstacle that the receiver won't see much debris. It should be ok; last year the receiver was mounted in the tub itself, and it survived beach use pretty well even with sand filling the tub. It should be about the same situation or maybe even better as the sand should fall out of the original battery space pretty easily.

The ESC should see good air flow even with the body installed...

IMG_1442.JPG

Still looks fine even with the internal modifications... Someday maybe a cockpit will go in there...

IMG_1443.JPG

A short test with the LiPo shows immediate improvement. Previously the motor would cog just a little at startup with the NiMH batteries; with the LiPo there is zero cogging at startup.

This is my favorite model for the beach. The large tires help it go over any sand whether it's dry and uneven or wet and hard packed; the power of the 4-pole brushless setup combined with a generous dab of antiwear grease in the diff makes it easy to fishtail and drift yet maintain control. All the electronics stay cool even with continuous running; I can run multiple battery packs back to back and not worry about motor/ESC temperatures at all. Now with the latest modifications, the occasional cogging is gone and startup is smooth. There's not much left to do except enjoy and maintain it now...

Hope y'all like it...

  • Like 4

Share this post


Link to post
Share on other sites

That looks *****en man!! Your detail work is second to none.. Awesome creativity and thought went into that one. It will be interesting to see if you notice if it handles different at all.. You will definitely get a heck of a lot more out of your runtime and a bit more punch. Glad to see it helped with the cogging as well.

Thanks for sharing! When my son gets a little more familiar with LiPo packs, we will definitely be copying what you have done here with his MadBull.

Share this post


Link to post
Share on other sites

Wow, I'm just doing a refresh on my brushless Mad Bull at the moment, but taking a slightly different approach. It's such a fun car, both in normal and pimped out form.

For the steering mod, did you have to trim the front strut to stop it from fowling?

Share this post


Link to post
Share on other sites

Good to see you're still finding a bit of time for RC action Paul - some nice improvements there, and still room for a driver figure above the battery by he looks of it (although Barbie's head might have to shrink a bit to fit now ! ).

I still have my NB kit - i really should get it built as these are excellent fun runners that can pretty much run on any surface.

Share this post


Link to post
Share on other sites

For the steering mod, did you have to trim the front strut to stop it from fowling?

No, I drilled a new hole in the steering bellcrank about 2mm closer to the pivot point so the turnbuckle will clear the stock shock tower. I'm using ball connectors from a DT02 Sand Viper servo saver; these are threaded with extremely small shafts and lock nuts. The change in hole location doesn't affect servo effort much.

  • Like 1

Share this post


Link to post
Share on other sites

You gaven me so many idea on my mad bull i just bought. i have same shorty battery i like the ideas...

Share this post


Link to post
Share on other sites

Thanks.

This model has gone to another TC member since last summer. If I had to do it again, I'd not use anti-wear grease in the rear diff as it was a little too stiff and made the model fishtail a little too much. I could tell after 10 minutes of running in the sand the rear diff had started to loosen up and it worked better that way. A thinner grease would be better to start.

Also, I had meant to install some stick-on automotive wheel weights in the original battery tray to add some weight and compensate for the lighter LiPo. The springs and dampers had been tuned for the NiMH battery originally. I didn't follow through, but I suspect an extra 50-100 grams of mass would give it some more rear traction.

Enjoy your Mad Bull; it's a great beach runner when modified and tuned!

Share this post


Link to post
Share on other sites

Need some video of this in action. :D

Edit, didn't read the whole thread, just looked at the pics. lol

Share this post


Link to post
Share on other sites

Well, JeepNMike has this model now, so he'll have to film it... It was built in 2012, upgraded to brushless in 2013, updated for shorty LiPo in 2014 (per this thread), and as far as I know he still has it in 2015...

Hey Mike, how about a video? :D

Share this post


Link to post
Share on other sites

Ah! I am glad I stopped in to see what you guys have been up to. I don't have a video, but do have a beach pic (below, with another at a basher track) where this buggy is best suited. I have Vanessa (Speedy's above), and my son has one that is very similar, just not as modified or as fast. I will say that Speedy's is crazy fast... Almost too fast really. I have my throttle end-point set to 80% to keep it driving with at least a little control with the 3250KV motor. I like to over-power my cars and use my controller and ESC to de-tune as needed vs. being unerpowered when I want the speed, but man this buggy is fast!! With the shorty LiPo pack, it is good for at least a 20-30 minute run depending on the terrain and it fits like it was supposed to be that way. I do echo what Speedy said above and adding some weight definitely helps the handling and traction.

Anyway, this is an awesome buggy for the beach and around the house! It actually is the most frequently used buggy I have (Thanks Speedy!).

IMG_1541_zpsfc096531.jpg

Two_Bulls_zpsc2dd0dd6.jpg

  • Like 1

Share this post


Link to post
Share on other sites

Just found this thread and it's cool to to see someone else having the idea with the shorty LIPO ;)

I have added a bit of carbon fibre to act as a top deck (to fix the battery and the ESC) and a servo mount, plus replaced the front suspension with parts from a DT-03. Handles pretty good now

Still need to add some weight on the rear though, the 3000kv outrunner is not helping with traction ;)

Share this post


Link to post
Share on other sites

Do you have any more details about your battery strap or some photos?

With these tires and any decent amount of brushless power, they are a handful huh? :lol: The one I got from Speedy, it takes a good 50 feet just to get it going straight at W.O.T. It is a good thing they are durable!! I wish the bodies were a little more durable, but they are good for a decent season of running before they start to look really tattered.

Share this post


Link to post
Share on other sites

Lots of good stuff in there (love the wheels too). Thanks for sharing!

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...