Battery for Tamiya Frog (1983)

[dr_gn]

All,

Just got some new tyres for my original restored Tamiya Frog from 1983, and I want to run it round the garden. It hasn't been run for about 35 years, but was mechanically restored about 15 years ago.

I'm going to get a new shell so I can keep the original (and more importantly it's original stickers) undamaged.

My son's got a Mad Bull, and some Overlander 3300 Tornado battery packes. Aparently 7.2V.

Will these be OK to run an original Frog, with it's original 3 step speed controller and resistors? They fit straight in.

My original 7.2v Tamiya hump battery was about 1200 mAh, and gave me about 20 minutes' running back in the day. Will the 3300's therefore give me about 50 minutes?

[ExPat2B]

There are two big problems.

1. A 6 cell Nicad pack has a MAX voltage of 7.2 volts ( 1.2v per cell )
A 2 cell lipoly pack has a MAX voltage of 8.4 volts ( 4.2v per cell )

The speed controller and radio MAY run on 8.4v but honestly there is a real risk of older stuff burning out.

The second problem is also voltage related. You CANNOT let the packs drop below 2.9 volts or they won't charge and should be considered scrap ( lithium forms spikes and disrupts the internal structure ) and you should ideally stop driving at around 3.6 volts depending on the lipoly discharge slope. . Newer speed controllers won't let this happen, they kill the throttle at 3.3 and stop working completely at 3 volts. So you need a voltage alarm/telemetry added to the standard Tamiya stuff.

the best solution is getting a more modern brushed ESC that is designed to work with the voltage and protect the battery.

[dr_gn]

ExPat2B said:

There are two big problems.

1. A 6 cell Nicad pack has a MAX voltage of 7.2 volts ( 1.2v per cell )
A 2 cell lipoly pack has a MAX voltage of 8.4 volts ( 4.2v per cell )

The speed controller and radio MAY run on 8.4v but honestly there is a real risk of older stuff burning out.

The second problem is also voltage related. You CANNOT let the packs drop below 2.9 volts or they won't charge and should be considered scrap ( lithium forms spikes and disrupts the internal structure ) and you should ideally stop driving at around 3.6 volts depending on the lipoly discharge slope. . Newer speed controllers won't let this happen, they kill the throttle at 3.3 and stop working completely at 3 volts. So you need a voltage alarm/telemetry added to the standard Tamiya stuff.

the best solution is getting a more modern brushed ESC that is designed to work with the voltage and protect the battery.

As I said, the Overlander is 7.2v. It's NiMH, so 1.2v per cell, and 6 cells. It's not LiPo.

[generationx]

Nevertheless the best solution is to fit an ESC. The mechanical speed controller and, more likely, the resistors will burn out easily.

Modelsport is your friend.

[dr_gn]

generationx said:

Nevertheless the best solution is to fit an ESC. The mechanical speed controller and, more likely, the resistors will burn out easily.

Modelsport is your friend.

I did that for the Mad Bull, and it works OK (never ran it with a mechanical controller).

I want to keep the Frog original - it ran fine on it's 3 step controller back in the day; is there a particular issue with modern batteries that burns them out?

Apart from the increased capacity/run time, if the voltage is the same as original I can't think of any reason it shouldn't work just as it did in 1983. Then again that's why I'm asking. I'm not planning on running it lots, just the occasional bleast around the house for old times' sake.

[300bhp/ton]

dr_gn said:

All,

Just got some new tyres for my original restored Tamiya Frog from 1983, and I want to run it round the garden. It hasn't been run for about 35 years, but was mechanically restored about 15 years ago.

I'm going to get a new shell so I can keep the original (and more importantly it's original stickers) undamaged.

My son's got a Mad Bull, and some Overlander 3300 Tornado battery packes. Aparently 7.2V.

Will these be OK to run an original Frog, with it's original 3 step speed controller and resistors? They fit straight in.

My original 7.2v Tamiya hump battery was about 1200 mAh, and gave me about 20 minutes' running back in the day. Will the 3300's therefore give me about 50 minutes?

yes it will be fine

[dr_gn]

First run after 34 years - still goes like a stoat:





I think generationx’s suggestion of an ESC might be possible while still retaining the original 3-step mechanical controller. It might fit where the (redundant) Rx battery holder would go.

My son’s got a cheap Modelsport Sniper 20 in his MB, but it’s a bit slow to go to reverse; doesn’t seem as responsive as the Frog.

[take-good-care-of-the-forest-dewey]

ExPat2B said:

There are two big problems.

1. A 6 cell Nicad pack has a MAX voltage of 7.2 volts ( 1.2v per cell )
A 2 cell lipoly pack has a MAX voltage of 8.4 volts ( 4.2v per cell )

The speed controller and radio MAY run on 8.4v but honestly there is a real risk of older stuff burning out.

The second problem is also voltage related. You CANNOT let the packs drop below 2.9 volts or they won't charge and should be considered scrap ( lithium forms spikes and disrupts the internal structure ) and you should ideally stop driving at around 3.6 volts depending on the lipoly discharge slope. . Newer speed controllers won't let this happen, they kill the throttle at 3.3 and stop working completely at 3 volts. So you need a voltage alarm/telemetry added to the standard Tamiya stuff.

the best solution is getting a more modern brushed ESC that is designed to work with the voltage and protect the battery.

I run loads of nimh rc kit on "7.2v" lipo. Tanks, Rock crawlers, cars. In every instance the electronics will cope with the slightly elevated voltage. You just need to be careful not to delete the battery.. Solved via a lipo charge alarm plugged into the balance charge cable.

[dr_gn]

So I tried the Modelsport ESC, but it didn't work. I think the Rx needs to be a BEC Rx? Mine's the old original Acoms ARB227 from about 1984.

I could get a newer 27mhz Rx, but then I doubt the old Acoms servo plugs (with their retaining clips) would fit the newer blade style sockets.

I wanted to stick with the original parts for old times' sake, but it looks like this won't be possible, even though a new, small Rx and the ESC would fit above the battery and be invisible.

[clockworks]

Pretty sure all receivers will work with a BEC. Are you sure you plugged the ESC into the Rx the right way round?

[dr_gn]

clockworks said:

Pretty sure all receivers will work with a BEC. Are you sure you plugged the ESC into the Rx the right way round?

Tried it both ways, the motor wasn't responding, just occasionally vibrated.

I notice some 27 mhz Rx's say "BEC" on them - doesn't this suggest there are BEC and non-BEC types?

Although I guess in 1984 they were so uncommon it wouldn't have been put on mine anyway.

[dr_gn]

clockworks said:

Pretty sure all receivers will work with a BEC. Are you sure you plugged the ESC into the Rx the right way round?

OK so an online search solved it: The +ve and -ve sockets are reversed on old systems. The signal pin is the same. I swapped the ESC power pins around, plugged it in to the old Acoms Rx and it worked perfectly:





So now I can keep all the old school look, but with ESC and won’t need separate batteries.

Surprising how massive the Mad Bull is compared with the Frog. Almost like the “Classics dwarfed by moderns” on the classic cars PH forum.

[300bhp/ton]

dr_gn said:

Surprising how massive the Mad Bull is compared with the Frog. Almost like the “Classics dwarfed by moderns” on the classic cars PH forum.

Except the Mad Bull is also a classic these days and of course is just like that thread. Where people compare big thing with small thing, then are amazed small thing is smaller than big thing..... :wheresthefalcepalmsmiley:

[dr_gn]

300bhp/ton said:

dr_gn said:

Surprising how massive the Mad Bull is compared with the Frog. Almost like the “Classics dwarfed by moderns” on the classic cars PH forum.

Except the Mad Bull is also a classic these days and of course is just like that thread. Where people compare big thing with small thing, then are amazed small thing is smaller than big thing..... :wheresthefalcepalmsmiley:

They're both described by Tamiya as being 1/10 scale, 2WD, off-road, high performance racing buggies. So the same scale, same function - even the same motor. For me, just bashing it around the garden, the Frog is way more agile, much more fun. The Mad Bull is a bit of a fat bd in comparison - it's also impossible to get it to track straight with the daft sized tyres too (and that's after I took the slop out of the steering linkages)

[300bhp/ton]

dr_gn said:

They're both described by Tamiya as being 1/10 scale, 2WD, off-road, high performance racing buggies. So the same scale, same function - even the same motor. For me, just bashing it around the garden, the Frog is way more agile, much more fun. The Mad Bull is a bit of a fat bd in comparison - it's also impossible to get it to track straight with the daft sized tyres too (and that's after I took the slop out of the steering linkages)

Madbull is bigger because it rides on monster truck tyres. The body and driver figure are the same scale as the Frog pretty much.

e.g. as a real life example:




Probably with the same engine too.


In a small space the Frog will be more nimble. But the Mad Bull should still run well. They run even better with a Lipo or Lipo & brushless upgrade.