How long should they last? Which batteries are most suitable? We asked Dave Catlin, designer of Roamer and Managing Director of Valiant Technology a few questions about the batteries for Roamer and Classic Roamer.
Q: Let’s talk about the new Roamer first. What kind of batteries do they use?
They use 6 conventional AA cells. As with the Classic Roamer you can use either rechargeable or non-rechargeable versions.
Q: How often do I need to recharge them?
We designed it so that normally you only needed to recharge the Roamer once a week. But, it is difficult to tell. So much depends on how you use the robot and the condition and age of the batteries. For example with young students you might do lots of simple activities so Roamer moves a lot. With older student they may take more time thinking and solving problems. So the Roamer is on a long time, but moves for a small part of that time. Moving takes a lot more power so in the second case you should need to charge the batteries more times. We regularly attend events where Roamer is used continuously for five or six hours. A fully charged, good condition set of Roamer Power Cells will manage that day without recharging.
Q: What happens if you forget to switch Roamer off?
After 5 minutes, the robot tells you it is still switched on. It will remind you 6 times and then it will automatically go into sleep mode to save power.
Q: You say Roamer Power Cells, but these are AA batteries – is there something special about them or can we use any AA battery?
They are special in sense that we have run extensive tests on their performance in Roamer and we know what they can do. There are a lot of cheaper batteries available, but usually that means they have lower capacity. As you can imagine we do not make the batteries. Like everyone else we source them from the Far East. Many suppliers offered us lower cost, but lower capacity options. What was concerning was when we said that was not high enough they offered to print whatever capacity we wanted on the label. So it is difficult to say what you can get from cheaper packages, we can only speak about the Roamer Power Cells.
Q: What kind of recharging system do you have?
We have an intelligent charger that allows you to fast charge the batteries. With the Classic Roamer we had a slow charger. This meant that you could leave the batteries on charge for as long as you wanted. The intelligent charger allows you to fast charge the batteries and when the batteries are fully charged, the charger switches itself off.
Q: That’s good: How long does it take to charge the batteries?
Again that depends. If they are absolutely flat and you’re using our charger, you can fast charge them in two hours. If you are just topping the batteries up then it will be a lot quicker. The intelligent charger senses when the batteries are full and switches off.
Q: Does this mean it is safe to leave on over a weekend?
Q: How do I know when to charge the batteries?
Roamer tells you! You still have some power left, but you need to charge the batteries as soon as you can. Using the Valiant intelligent charger you can put in enough power over the lunch hour to continue working with Roamer in the afternoon.
Q: What is battery memory and do you get this problem with these batteries?
With Nickel Cadmium (abbreviated Ni Cad) batteries, if you drained them to the same point and then recharge them you would find the capacity of the battery dropped. This problem does not occur with the type of battery we provide.
Q: We had problems with Classic Roamer batteries – will it be the same?
No. It’s a different type of technology. It uses Nickel Metal Hydride (abbreviated as Ni-Mh). All batteries deteriorate if you leave them discharged. The Classic Roamer uses Lead Acid Batteries and their problem is that you must never leave them discharged for any length of time – a week is too much. These are much more tolerant, although it is always a good idea to make sure you store the batteries fully charged.
Q: Why did you not use Ni-Mh technology with Classic Roamer?
It was not invented when we developed the Classic Roamer and nobody makes Ni-Mh Lantern Batteries.
Q: Why did you choose those big batteries in the first place?
Our experience with the Turtle told us that long battery life was critical. The batteries used in Turtle were similar to those in the new Roamer. However, in those days their capacity was a lot lower – about 30% of today’s batteries. What would happen is teachers would plan a lesson and suddenly found out that the batteries were not charged. And because the batteries were charged on-board the robot the lesson was effectively over.
Q: Is that why you do not charge batteries on-board Roamer?
It is one reason. If you suddenly find that the batteries have no charge you can quickly change them for another set. It is worthwhile keeping a set on non-rechargeable batteries available for this purpose. Safety is another issue. If you used non-rechargeable cells, someone could try and recharge them. This is dangerous.
Q: You can get Ni-Cad versions of those big batteries and they are cheaper. These don’t deteriorate like Lead Acid batteries. Why not use them?
We did to start with. But they are not very green. European Union legislation banned them. That is why the battery industry developed NiMh cells.
Q: What things affect battery life?
Roamer uses less power when it is being programmed than when it’s running around. Most of the time young children and novices simply write simple, short programs that move the Roamer for a large amount of the time it’s switched on. Older children spend more time programming.
The ratio of running time compared to the time Roamer is switched on is the most important factor affecting battery life. Programs with much starting and stopping use a lot of battery power. Running the Roamer on a smooth, hard, surface uses less power than running it on a surface such as a carpet. Sometimes you get more running life from the Classic Roamer batteries by switching them around. To save power you should always switch off the Roamer when it’s not in use. The Classic Roamer sounds a warning when it has been switched on, but not used, for five minutes. After six warnings it switches to low power and clears its memory. The new robot asks you to turn it off.
Should I use rechargeable or non-rechargeable batteries with Classic Roamer?
It depends on how you use the Roamer. You should test how long a set of non-rechargeable batteries last. This will vary with each situation. We recommend you install a pair of PJ996 lantern batteries and see how long they last. You can purchase non-rechargeable batteries very cheaply see here You can then work out how long it would take to repay the investment on the rechargeable pack.
If you use the Roamer with the Control Box, which uses more power, the rechargeable battery will be more economical.
Q: How do I know when to charge the batteries in Classic Roamer?
When Roamer starts to behave erratically it is probably time to change the batteries. Occasionally new PJ996 batteries are defective, so you may have problems after installing them. If this happens replace them and return the faulty ones to the supplier.
Q: How does using the Roamer control features affect the batteries?
The Roamer may behave satisfactorily when running simple programs but erratically when using its control features. This happens when the battery voltage drops because motors etc. draw more power. Because of its flat discharge characteristics the Rechargeable Battery/Charger pack is more suitable for control work.
Some output devices such as cheap motors may cause sudden fluctuations in voltage, which also cause the Roamer to behave strangely. Valiant produced output devices avoid these problems.”
Q: Is there anything else we should know about Roamer and batteries?
If the Roamer is not going to be used over a half term break or longer it is advisable to remove the batteries from the robot. Also take the batteries out of Roamer when it is in transit, to prevent damage.
Q: Thank you for the information.
It’s a pleasure.