Ford Ranger F150 XLT - Non Standard Heat Sink

[hifih66]

This is my first post so sorry if this has been asked before. I can't find reference to it by searching the forums.

I bought my Ford Ranger F150 XLT in 1983 and I've owned it ever since. I built it back then and put it away about twenty years ago. I got it back out of the box recently and updated the shocks to the re release version and replaced the (dead) NiCad battery with a lithium battery, otherwise everything is as I built it 38 years ago.

When I ran it on the back lawn overy the summer (very short grass and dry) the motor housing became quite warm. When I decided to investigate I found that the heatsink was not standard, in fact it didn't exist and in it's place was a transistor type device. (Picture attached) I don't recall ever changing this from new and I'm pretty sure it's the original speed controller. I have the original handbook but it's not shown in there.

As anybody got any documentation on this?

[hifih66]

Found out that it's an Acoms AP35 Speed controller. Now to find the instructions.

[hifih66]

I've found the handbook now. Guess I should have looked a bit further before posting.

[LEE71]

Nice one. Love to see more pics!

[hifih66]

Here's a couple.

[Busdriver]

20 minutes ago, hifih66 said:

Here's a couple.

❤️😘😊😍🥰💕💖💙💗💜💔💞💓❣️😻🤟

[sosidge]

I do like seeing these old ESCs. That must be one of the very earliest? Really "crude", not even any heatshrink, let alone a case!

I'm sure it cost a pretty penny back in the early 80s, surprised you forgot about fitting it!

[El Gecko]

5 hours ago, hifih66 said:

replaced the (dead) NiCad battery with a lithium battery

Not sure what lithium battery you're using, but I'd hesitate to put even 2S power through that old ESC.

[SuperChamp82]

Very nice find !

The old Acoms AP-35 is 6A contionus (peak 30A) ESC from the early 80s, with an old type / pre-FET, ‘Darlington’ transistor set.

@sosidge is also spot on - they were v expensive (+ therefore relatively hard to find back then) so you must have had decent birthday or Christmas present 😂

Darlington transistors were designed in the 50's, and used to be called "Darlington pairs" or "Super Alpha Circuits" - as they contain two separate transistors acting like one, where the second one further amplifies the current from the first.

The disadvantage of all that is a voltage drop of about 1v from input to output - which is obviously a fairly big problem for RC cars.

The relays are there for then bypassing the transistors on full speed, to help eliminate that voltage drop.

Newer ESC's with FET transistors have much smaller voltage drops - removing the need for bypass relays.

A funny thing with some of those old Darlington ESC's is that they have a slight delay before the relay takes over - almost like the "turbo lag" on Porsche 911 (930) turbos from the 80's ! 

In terms of battery / motor size, I’d steer clear of anything beyond standard 6v packs and 540S motors or something mildly tuned - like an old Black Sprint or Endurance 👍

 

[svenb]

That's in fantastic condition considering it's age👍

[hifih66]

13 hours ago, sosidge said:

 surprised you forgot about fitting it!

I was 36 years old when I built it. I can forget anything I like now.

[hifih66]

8 hours ago, SuperChamp82 said:

Very nice find !

The old Acoms AP-35 is 6A contionus (peak 30A) ESC from the early 80s, with an old type / pre-FET, ‘Darlington’ transistor set.

@sosidge is also spot on - they were v expensive (+ therefore relatively hard to find back then) so you must have had decent birthday or Christmas present 😂

Darlington transistors were designed in the 50's, and used to be called "Darlington pairs" or "Super Alpha Circuits" - as they contain two separate transistors acting like one, where the second one further amplifies the current from the first.

The disadvantage of all that is a voltage drop of about 1v from input to output - which is obviously a fairly big problem for RC cars.

The relays are there for then bypassing the transistors on full speed, to help eliminate that voltage drop.

Newer ESC's with FET transistors have much smaller voltage drops - removing the need for bypass relays.

A funny thing with some of those old Darlington ESC's is that they have a slight delay before the relay takes over - almost like the "turbo lag" on Porsche 911 (930) turbos from the 80's ! 

In terms of battery / motor size, I’d steer clear of anything beyond standard 6v packs and 540S motors or something mildly tuned - like an old Black Sprint or Endurance 👍

 

Thanks for great advice. It's given me some leads on reducing the heat, but first check if its the motor housing or the Darlington transistor that's getting warm when running. ESC has worked fine for 38 years and haven't noticed any lag but there again it's the only model I've ever owned. Guess the new Li-ion battery can sustain a higher voltage that lasts longer compared to the old NiCad. Remember Darlington Pairs and MOSFET's from my Electronics training back in the late 60's (and also from my other hobby, Hifi). I have never had any interference on 27MHz and models have moved on, as has CB Radio. Don't fancy changing out the whole electronics chain.

Edit:

I've decided on what action to take to reduce heat to Motor/Transistor.

1. Replace Wheels/Tyres/Bearings - they need it anyway.

2. Replace 7.2V Lithium Battery with 6V Lithium Battery. I can get one from the same series which uses the same charger. I think reduction in voltage will reduce current through transitor and 6V battery can also power electronics instead of current set up of  4  x 1.5V cells.

 

Edited November 3, 2021 by hifih66
Update

[casethejoint]

Lovely F150 and nicely built too

I have several of these AP-35s (a few years ago there were plenty on eBay being sold for model trains - I guess they were used for those too, with PCM modulation being sent down the rails maybe?). Back in 1983 it was a big upgrade on the mechanical ESC that came with SRBs and there weren't that many other options.

The transistor will fry if even a stock 540 motor if it's under too much load with 7.2v, so I think under-powering it is a good idea. You can still buy the transistors thankfully - plentiful supply on eBay.

I now have as my main SRB runner a F150 same as yours but I opened up the Acoms receiver case and sneakily stuck a 2.4ghz digital RX inside the case, so it looks like a regular vintage Acoms but actually all modern no-glitch digital. If you look closely at the pic you'll see the two antennas poking out the antenna wire hole.

I run this with a 6.6v (I think) LiFE battery and a vintage black 540SD. Lots of fun - totally vintage but the modern Rx makes a big difference to my confidence that it's not going to careering off on its own.
 

 

[GeeWings]

What a beauty. Good luck with bringing it back to life and look forward to updates.

[hifih66]

Well I've finished the 6V conversion and fitted new wheels and tyres with new sealed bearings. It already had new version shocks and chassis pins from last year. I accidentally beheaded  the driver when polishing up the paint work but it was only a case of dried out cement and easily fixed. I connectorised the Jadlam 6V battery to the On/Off Switch and connectorised the battery cage should I ever want to revert to 7.2V working. Incidentally the battery had a plug fitted to the secondary output (rather than a socket) maybe it's to fit some other part of which I'm not a aware. I corrected mine. It runs fine but the weather isn't conducive to testing today. I have to confess that, although I actually built the car it actually belongs to my son and he never took it with him when he left home 20 years ago. I've been restoring it for his son so that when he's old enough he can take up the hobby. But now I've got a second grandson and I've so enjoyed working on this one that I'm on the lookout for an equally vintage Sand Scorcher/Rough Rider/Ranger to restore for him. Soldering the secondary battery terminals was fun, but no mishaps.