Getting Big Bear running again

[vmt79]

Hi!

I have an old Big Bear I built in 1990. It has been standing for years. I'm now going to run it again. I bought a new 7,2V NiMH battery stick pack for it. However, when trying it to the car's battery compartment it didn't fit. It's longer than the compartment by about half a centimeter. The battery compartment is around 132-133 mm long and my new battery is 138 mm. My old NiCds from 1990 just fit it. I have now searched from the net different battery brands and their dimensions and it seems the new batteries almost always are longer than Big Bear's compartment. I have found a couple of batteries which probbaly have shorter length (for example 130 mm), but at the same time they seem to have more width (around 48 mm) than the battery compartment's width at both ends which is narrower (45 mm). So even though the shorter batteries would be short enough they probably wouldn't fit either because they won't fit at the ends. My new battery is also about 46 mm in width, so it's just a bit too wide as well.

I would like to ask are there people who are able to fit normal 6 cell 7,2V NiMH stick packs to their Big Bears? I mean that those batteries are relatively new and still in stores. Big Bear's compartment feels just too small for today's NiMHs to fit. I'm thinking if I should just cut off one of the battery compartment ends. Ì'm not sure if it affects the strength of the chassis. I have however already cut out part of the other end for the battery wires and therefore I don't think it makes that much difference to cut the whole end off. Has anyone done this or are there other solutions? I would rather not modify a battery pack myself so looking to other kind of solutions

The car is in good condition apart from the tires which are a bit shot on the sidewalls and probably don't take much harder running. I managed to get a set of tires in better condition on sidewalls and also some other spare parts including a chassis. However, these tires have a couple of flat spots and probably would need foams inserted. Of course I'm wondering if they would survive the work needed for the foams. I have read some people have put Lunch Box tires to Big Bear. Is this the best option if you can't get good condition original tires? Or are there some other tires that would be about the same size? I have searched quite a lot, but it seems those probably are the closest. How about Kyosho Mad Van tires? Or CEN Racing monster truck tires, which seem to be also about the same size: https://www.cenracingusa.com/products/cq0503 But other tires probably don't fit the original rims and would need some adapters to other rims.

I would appreciate any help

[LurkingCAT]

Good project you've got going! Big Bears are great fun and at times frustrating. It was my only non-racing car in the eighties and good fun to bring along for holiday trips when there were no tracks around.
I don't have any to add on your tire question as it seems you've found the different off the shelf ones that are sort of fitting. I think both width, section height and pattern are an important signature of the car, so I've aimed for original ones and also tried the slightly smaller Lunch Box/Pumpkin ones.

For the batteries I see you are looking into NiMHs. Ever considered another route? I use shorty LiPo in mine, and they have loads of capacity and a very good fit with some dense foam blocks. I'm not quite sure about what you are saying about additional cutouts and effect on the chassis. From my experience the Marui chassis plastic was brittle from new and certainly not better after 30/40 years. All cut outs (especially vertical sections in the middle of the chassis) will decrease stiffness and potentially bring you closer to fracture on and impact. You see mine has also got old cut outs, but would never expand these. Now I stay away from all cut outs of the chassis. I've even put in some extra supports in weak places as seen in the last picture.

[silvertriple]

I have some Lipo stick packs 134 mm long (at the longest area) which fits all my vintage cars without any single modifications to the chassis, and it's working for my Big Bear as well...

[vmt79]

Good project you've got going! Big Bears are great fun and at times frustrating. It was my only non-racing car in the eighties and good fun to bring along for holiday trips when there were no tracks around.

Thanks for your reply. Yes, it is a fun car. It's my only proper RC car I have got and build. Had some market cars before that when I was a little kid I ran it relatively little during the time and it has been sitting I think about 20 years since I last ran it. Apart from the tires it should be in good condition.

Would also like to use original tires. Somehow they look the best even though they are quite wide. But what I have seen photos of Big Bears with Lunch Box tires on my mind they look quite ok.

About the batteries. My idea is first to just get the car running and check if everything still works fine. I have all the original electronics. For now this is not that much of a hobby for me. I don't know yet how often I will run. But I'm now interested to run the car again and I have read quite a lot from different forums and so and get to know what's the situation with parts today and so on Ok, LiPo could be smaller and fit better. But I'm somehow not just that interested in with all the extra care that I understand seems to relate LiPos. It also didn't help that my neighbour, who has RC more as a hobby, recently almost burned his house when his LiPo battery exploded inside and started a fire. He had to renovate one room because of it... The NiMH battery I bought was sold to me with dimensions that weren't true and I'm now trying to get it changed to shorter one. Which is then a few mm too wide, but I think should fit in when you tilt it a bit. I'm not too interested to cut the chassis even though thought that as one option.

[vmt79]

I have some Lipo stick packs 134 mm long (at the longest area) which fits all my vintage cars without any single modifications to the chassis, and it's working for my Big Bear as well...

Ok a 134 mm still fits your chassis. Is it very tight? I think there is some variation in different chassis. I just got a used spare chassis and my old NiCds fit it tighter than in my original chassis.

You haven't made bigger battery compartment to your 3D printed chassis? I have read what you have done for Marui cars and created those 3D printable parts. I really admire your work! That's really great

How have your printed gears lasted? Are they ok for longer use?

[silvertriple]

I have some Lipo stick packs 134 mm long (at the longest area) which fits all my vintage cars without any single modifications to the chassis, and it's working for my Big Bear as well...

Ok a 134 mm still fits your chassis. Is it very tight? I think there is some variation in different chassis. I just got a used spare chassis and my old NiCds fit it tighter than in my original chassis.

You haven't made bigger battery compartment to your 3D printed chassis? I have read what you have done for Marui cars and created those 3D printable parts. I really admire your work! That's really great

How have your printed gears lasted? Are they ok for longer use?

There is 2 versions of the chassis. The V1 was not intended for 7.2V stick packs (it was for 6V packs, so too tight for 134 mm packs) and the Big Bear exclusively used the V2 version of the chassis (V1 was for the first gen of the Super Wheelies). Here is the 134 mm lipo 4000 mAh stick pack in the original Big Bear chassis. This chassis was used as test bed for my Big Bear gear set, and it is an original chassis.



And for my printed chassis, there is slightly more room for the batteries in it. Beside the reinforcements here and there, it works with slightly larger batteries (I have a few 138mm packs and they are not working on many of the vintage cars, although they are stick packs, but they are working fine in my enhanced chassis).

Another comment, for the tires, the Big Bear works well with custom rims and Tamiya Lunchbox tires. They are the same diameter as original Big Bear tires, but the Big Bear tires are quite larger. The difference makes it more enjoyable to ride as per my experience...

[coxbros1]

Never new that there were 2 versions of the chassis...great info!..
I currently have a Big Bear in restoration that just wouldn't hold 6 cells in line....so i am assuming it's a V1....my 1st ever R/C was a Big Bear in 86'....but I can't remember if it ran 6 volts, 7.2 volts or if I cut the chassis to fit...I just can't remember (prolly too much booze over the years)

[silvertriple]

Never new that there were 2 versions of the chassis...great info!..
I currently have a Big Bear in restoration that just wouldn't hold 6 cells in line....so i am assuming it's a V1....my 1st ever R/C was a Big Bear in 86'....but I can't remember if it ran 6 volts, 7.2 volts or if I cut the chassis to fit...I just can't remember (prolly too much booze over the years)

The Big Bear was 7.2V chassis only. The first Big Bear I got was coming with a 6V chassis, swapped at some point by the previous owner. There was also different colors for Super WHeelies (black chassis, 6V in first version, 7.2V in second version) and Big Bear (brown or dark grey - 7.2V). The other key difference between the chasssis version is that 7.2V version had slot for the steering servo post mount (but holes remained to do by the builder - the Super Wheelies did not used the servo post, the servo was supposed to be glued inside the bath tub on those).

I've tried to detail all my findings in my thread on the Super Wheelie and Big Bear...

[vmt79]

There is 2 versions of the chassis. The V1 was not intended for 7.2V stick packs (it was for 6V packs, so too tight for 134 mm packs) and the Big Bear exclusively used the V2 version of the chassis (V1 was for the first gen of the Super Wheelies).

Yes, this I knew that there are two versions. What I meant with my comment was that for some reason my old battery fits slightly tighter to my original chassis than the other, both are V2. Maybe there's some slight tolerance which I can't measure or it has just streched a bit

Another comment, for the tires, the Big Bear works well with custom rims and Tamiya Lunchbox tires. They are the same diameter as original Big Bear tires, but the Big Bear tires are quite larger. The difference makes it more enjoyable to ride as per my experience...

Good to know that. It probably would be the easiest route to use those Lunch Box tires then if the originals can't be used.